Animal Spirit Doctrine and the Origins of Neurophysiology 0199766495, 9780199766499

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Title Pages

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Title Pages (p.i) The Animal Spirit Doctrine and the Origins of Neurophysiology (p.ii) (p.iii) The Animal Spirit Doctrine and the Origins of Neurophysiology (p.1) The Animal Spirit Doctrine and the Origins of Neurophysiology (p.2)

(p.iv) Oxford University Press, Inc., publishes works that further Oxford University’s objective of excellence in research, scholarship, and education. Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Copyright © 2012 by Oxford University Press, Inc. Published by Oxford University Press, Inc. 198 Madison Avenue, New York, New York 10016 www.oup.com

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Title Pages Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. ______________________________________ Library of Congress Cataloging-in-Publication Data The animal spirit doctrine and the origins of neurophysiology / C.U.M. Smith…[et al.]. p. cm. Includes bibliographical references and index. ISBN 978-0-19-976649-9 (alk. paper) 1. Neurophysiology—History. 2. Neuroscience—History. I. Smith, C. U. M. (Christopher Upham Murray) QP355.2.A55 2012 128’.109—dc23 2011037109 ___________________________________ 987654321 Printed in USA on acid-free paper

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Dedication

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Dedication (p.v) To our wives—Jenny, Ana María, Wendy, and Dottie—and families, from whose sight we have sometimes disappeared for days at a time while working on this tome, and to lasting friendships among colleagues (p.vi)

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Preface

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.ix) Preface What is the physical basis of mind? How does the brain work? How are the commands of our will transmitted to the body’s muscles? How do we become aware of our surroundings? These are questions that have puzzled thinkers from the earliest times. For at least two millennia the answers to these questions made use of the concept of “animal spirit”; only in the past 200 hundred years have the answers been formulated in terms of electricity. This book follows this millennial history from earliest times. It shows how the idea of an intrinsic “animal spirit” emerged in classical antiquity and was refined in late classical and medieval times, only to encounter observations in the Renaissance and experiments in the Early Modern period showing that some of the fundamental assumptions of this earlier way of thinking could not be verified. It was during the second half of the 1700s that what would become known as a “paradigm shift” began to occur. The concept of animal spirit was replaced, not all at once, but ultimately completely, by the experimentally validated theory of animal electricity, which has grown into the neurophysiology we have today. The story is a fascinating one. It traces the history and foundations of our present-day understanding of the nervous system. Yet it has seldom, if ever, been told from start to finish, and for this reason is little understood or rarely taught, even by historians of the life sciences.1 Indeed, most histories of the discipline we would now define as neurophysiology are restricted to the modern era and devote just a few paragraphs, if any, to the great narrative of what went before.

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Preface We hope that our book will help to rectify this historical omission and some of the distortions spawned by the absence of a good source on this subject matter. Nevertheless, a disclaimer is in order right from the outset. The idea that anyone or even a team of historians could write a complete history of the doctrine of animal spirit has to be dispelled. The primary literature is simply too vast, since at its root this concept permeates so many different fields, of which we could mention philosophy, physiology, medicine, and theology, to name just four. Moreover, each of these fields is itself vast, each has many representatives saying the same or slightly different things, and each can be approached in more than one way. As a result, choices have to be made and the end product must, of necessity, be a construction based on subjective decisions. Our book is no exception. Our focus is not on every facet of the animal spirit doctrine, but on how it formed the basis of early neurophysiologies, allowing philosophers and physicians to “understand” how, for example, we might perceive a visual image, flex a muscle, or perhaps even recall a memory. In addition, knowing it would be futile to try to cover the views of hundreds of early thinkers, we restricted our account to those individuals whose works and names are generally better known, for the most part people regarded as leading figures in the history of philosophy, and then in medicine, and more specifically physiology. Such an approach has made our subject matter more manageable, and it allows us to tell this story in a book of reasonable size. It also leaves the door open for deeper scholarly studies on various facets of what we are covering, as well as for alternative approaches to our subject matter, which we certainly hope this initial but modest attempt at a synopsis will stimulate. This book, a long time in coming, integrates the work of four authors from three countries on two continents. It would not have been possible without modern electronic means of communication. Our email inboxes have been filled week after week with questions and comments, drafts and revisions. It is, therefore, useful to say a few words about how we came together to research and write on this topic.

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Preface The idea originally came from Will Clower, who was particularly interested in 17th- and 18th-century neuromuscular physiology, and what led to the paradigm shift whereby the older animal spirit doctrine was replaced by electrical ideas. Several years after Will had produced a preliminary draft, and now being engaged in a non-academic career, he met with Stan Finger and asked him whether it might be possible to make what he had started into a publishable book. Stan agreed but immediately recognized the need to greatly expand Will’s converage. He wanted to include a number of chapters on the origin of the concept of animal spirit in the ancient world, its role during medieval times, and much more information on how electricity emerged as a potent force in physiological thought. With these thoughts in mind, he persuaded Chris Smith and Eugenio Frixione, who had different areas of historical expertise, to join in the enterprise and help produce a more encompassing history that would have even broader appeal. We thank Will for his generosity in allowing us to take what he had written and then to modify, expand, and frame it in broader contextual ways. A greatly expanded outline followed, and it was decided that each of the authors would write and take final responsibility for different chapters, which would then be circulated for comments and approval. The work was accordingly (p.x) divided as follows: Chris Smith was the lead author on the Prologue and on Chapters 2, 4, 6, 7, 8, and 9 as well as on the introductions to Sections 3 and 4 and the chronologies; Eugenio Frixione took charge of Chapters 1, 3, 10, 11, and 12, plus the introductions to Sections 1 and 2; Stan Finger was responsible for Chapters 13, 14, and 15 and the introduction to Section 5, while also assuming the invaluable role of general critic and copy-editor; and Will Clower took on the initial drafts of the epilogue. Chapter 5 was a particular instance that involved close cooperation of Chris, Eugenio, and Stan. But as it turned out, all chapters and the prologue and epilogue involved considerable cross-fertilization, with different authors contributing different perspectives, interests, and expertise. Hence, as we worked through the book, the chapters came increasingly to reflect the combined thoughts and expertise of the group as a whole. Looking back, we feel that the strategy we adopted in bringing the book to fruition was advantageous. The different approaches, perspectives, and questions of the four authors combined to illuminate different aspects of a complex topic, and allowed us to present a better understanding of the individuals who played key roles in our history and of the changing times in which they found themselves.

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Preface We hope this book will appeal to both general readers and neuroscientists interested in the history of their subject. To this end, we have attempted to keep the style accessible to all, while providing many quotations (or translations of such) from original or early sources. Further, we have provided bibliographies and in some instances reasonably detailed references, so that historians will be able to find the sources and some of the vast scholarly literature that followed these seminal writings. Finally, a preface provides an opportunity to acknowledge the many people— fellow workers, teachers, colleagues, librarians, editors, friends, and, far from least, family—who have helped with advice, knowledge, and patience as our book has taken shape. Without them this work could not have been completed, and we thank them all. With all of this in mind, we hope that this book will be read by all who wish to follow the intriguing story of how, over the millennia, we have come to understand the workings of that most important of our possessions, our nervous system. Notes:

(1) See Rothschuh, 1958, and Glynn, 1999, for two rare monographs in compact form.

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Prologue

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.xi) Prologue C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

We are like dwarfs sitting on the shoulders of giants. John of Salisbury, 1159: Metalogion; afterwards used by Isaac Newton and others This book follows the rise and fall of an ancient and powerful idea: the notion that something external is incorporated into the human frame and acts as a messenger between mind and body. This imagined and mysterious courier travels along nerves to and from the brain. Being invisible and coming from outside, like a breath, as well as being incredibly fast, it was ranked in the category of spirits—in the special class known as “animal spirit” (i.e., that intimately related to the soul [anima]). This construct, with roots deep in antiquity, remained pre-eminent for nearly two millennia in Western science and medicine. Over time, it would be challenged: first with the call for new learning during the Renaissance and then with the experimentation and scientific rigor that marked the Early Modern era, a period of time that included the transformational 17th and 18th centuries. Gradually, the older notions of an animal spirit coursing through hollow nerve canals melded with newer anatomical, chemical, and mechanical ideas, and ultimately a new physiology based on animal electricity emerged and slowly took hold. If looked upon from the opposite end of the bridge, we could state that this book is about how electricity replaced a long line of fascinating but speculative thinking about the functioning of nerve and brain.

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Prologue Thus, the chapters that follow will trace the growth of the idea of animal spirit from its misty beginnings in preliterate societies to its emergence as the dominant theme in ancient and medieval medical lore. We then examine its slow demise over centuries, as natural philosophers fought to modify it in response to new discoveries, and then to weigh these conceptions against alternative concepts. This history, involving some of the greatest intellects the world has known—including Plato, Aristotle, Avicenna, Albertus Magnus, Andreas Vesalius, René Descartes, Isaac Newton, and even Benjamin Franklin—presents one of the greatest of all philosophical and scientific journeys. It has both characterized and transformed Western civilization. It provides, moreover, a clear example of a paradigm change:2 the replacement of millennial medical teaching about how the nervous system operates, in which keen observations were blended with supernatural notions, with a naturalistic physiology based solely on physics and chemistry. But let us start at the beginning. That breath and life are associated must have been as obvious in Paleolithic times as it is to us in our electronic age. This is confirmed in the earliest written records that have come down to us. In Genesis we read of how the Lord God formed man out of the dust of the ground and breathed into his nostrils the breath of life. An analogous concept was widespread throughout the ancient world. At the root of Indo-European language, Sanskrit, we find the word prana meaning “breath” or “life force.”3 In the Indian folk tales collected as the Upanishads, the earliest dating from about 800 BCE, prana is conceived to be part of the environment, suffusing all things and providing the energy that sustains both the physical body and the mind. In traditional Chinese culture the term qi has a rather similar connotation, meaning something like “energy”—the active principle in living creatures—and the etymology shows that qi, too, was originally related to “air,” or “breath.”4 It is, of course, difficult for us in our 21st-century scientific culture to fully grasp the meanings of these ancient terms; they relate to thought-worlds very different from our own. It does seem clear, however, that the notion of some external energy entering and vivifying the body in the process of breathing, and then leaving it permanently when the body dies, had been widespread in ancient times.

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Prologue In this book it is the Western tradition that we intend to follow, so we shall leave the Middle Eastern, Indian, and Chinese worldviews and instead open with the somewhat similar ideas current some two and half millennia ago at the beginning of Western science and philosophy, in Greek antiquity. Here we immediately meet the notion encapsulated in the term Greek term pneuma (πνευμα), intimately associated with psyche (ψυχή or soul), “the sign of life, or the (p.xii) life spirit.”5 These terms all originally had to do with air, breath, breathing, and movement. They confirm, once again, that rather similar notions pervaded the ancient world, both east and west and that in all probability they originated in the age-old recognition in preliterate societies that breath and life, from first to last, come and go together. Very early in this tradition, a fragment from Anaximenes tells us that the environmental pneuma is also involved both in holding the body together and in controlling its activity.6 We shall see that this notion recurs in a more elaborate form in the “psychophysiology” developed by Herophilus and Erasistratus at the Alexandrian Museum several hundred years later, during the second century BCE. Pneuma, or its Latin translation, “spiritus,” continues, moreover, through Galen into the medical theories of medieval times and on into the emerging physiology of the 17th and 18th centuries of our era. As already mentioned, the connotation of pneuma is closely related to that of the term psyche, which also originally meant “breath.” Psyche is translated into Latin as anima and is cognate with the English word “soul.” These words have, of course, vast and imprecise connotations. Throughout the millennia they have energized wide areas of Western thought. As Alfred Crawley points out, “Few conceptions can show the universality and permanence, the creative power and morphological influence, which have characterized throughout history the Idea of the Soul.”7 At the beginning of the Western tradition, we can trace them at work in the Homeric poems. In the Iliad, there is much talk of the soul. Hector dies and “the soul went forth from his limbs and flew toward the House of Hades, wailing her doom, leaving youth and manhood behind her.”8 Earlier in the Iliad, Achilles affirms the relationship between psyche and breath by vivid imagery: “For by harrying may cattle be had and goodly sheep. And tripods by the winning and chestnut horses withal; but that the spirit of man (ψυχή) should come again once it has passed the barrier of his teeth, neither harrying availeth, nor winning.”9 Once the psyche escapes, there is no coming back.

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Prologue The equation of psyche with the breath is common among the Homeridae.10 Indeed, this equation still moves deep in our language today. Do we not still give a blessing when an acquaintance sneezes? The conceit is that during a sneeze the soul leaps out like a lizard’s tongue. And do we not still use the same word —“expire”—for death and the exhalation of breath? These linguistic fossils from more ancient times still faintly stir in our commonplace speech. It is not difficult to see that they refer back to the times when the phenomena of fainting and dying suggested that some animating principle departed with the breath and was, in fact, nothing but the breath.11 Indeed, according to the classical scholar A. W. H. Adkins, neither in Homer nor in any other early writer is the concept of the “spiritual” as opposed to the “material” to be found.12 Psyche is conceived as a very fine, tenuous material that flies out of the body at death and descends to Hades (Fig. P.1). Further, as Adkins remarks, this seems to have been its primary function—simply to survive death. Its esse, it has been wittily said, is superesse (to be is to survive). It was only when firm definitions of inorganic matter became available, and this as we shall see was long in coming, that (p.xiii) it was felt necessary to “hypostatize” a separate “spiritual” or “mental” substance.

Figure P.1: Hermes Psykhopompos (guide of souls) leads the soul of a woman to the skiff of Kharon. Kharon leans on his staff. Vase painting, c. 450 BCE. (National Archaeological Museum, Athens)

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Prologue From all of the foregoing it is easy to see how psyche, the Homeric breath or life “soul,” came to be associated with the head and mouth. The Homeridae, however, also recognized a number of other quasi-psychological terms, of which the most important was a feeling and emotional soul that they understood to be located in the torso, in the region of the diaphragm. This second more “soulful” soul was connoted by the word thymos, a word having etymological connections with Latin fūmus and Sanskrit dhūmas, both of which have been translated to mean “vapor” or “smoke.”13 Thymos was conceived to have a controlling influence on bodily activity: it was at the promptings of thymos that the hero sprang into action. Unlike psyche, thymos disappeared with the body’s death. According to Adkins, the ancients regarded it as responsible for the “swirling, surging—sometimes choking—sensations of anger and other violent impulses.”14 It reappears in the Timaeus as Plato’s “warrior soul.” Once again one is aware of the lack of distinction between the physical and the psychological. At the beginning of the Western tradition, as throughout the ancient world, our modern categorizations are missing. The world is unified: “All things,” as the first of the pre-Socratic philosophers, Thales, is reported to have said, “are full of gods.”15 Psyche, thymos, and other Greek terms have both psychological and physical properties. There is, as yet, none of the sharp distinction that moderns make between the animate and the inanimate. That distinction was slow in coming. One major strand in the history of its emergence forms the subject matter of this book. The narrative is complex and many-sided. The ancient hylozoistic view of the natural world, the world of antiquity and the Homeric poets, withdrew as monotheisms and new technologies and ways of looking at the world advanced. John Milton’s celebrated poem, “On the morning of Christ’s nativity,” describes the sound of wailing around the grief-stricken shores of the pagan world on that first Christmas day—“From haunted spring, and dale/edg’d with poplar pale/The parting Genius is with sighing sent.” This is one aspect of the long withdrawal: the pagan world, alive with personified forces, is swept aside. But more than this, and perhaps associated with monotheism, comes the rise of technology and a manipulative attitude to the world. This reached a tipping point in the Renaissance and in the early modern world of Kepler and Galileo, Francis Bacon and René Descartes. It seemed finally to eliminate the ancient perception of a living, ensouled world, and to usher in the very different world in which we live today. Materialism, furthermore, reaches not only into the natural world but also into every cranny of our physiology. And, most importantly, so far as this book is concerned, into the ways in which brains receive sensory information and control bodily activities.

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Prologue This forms the topic of our book. We shall see how the ancient ideas of pneuma and psyche, long equated with wind and breath, sharing both psychological and physical characteristics, were eventually discarded and replaced by materialistic ideas involving chemistry and electricity, and ultimately, in our day, by the subtle actions of voltage-dependent, membrane-bound, proteins. The story is a fascinating one. It involves theologians, philosophers, and scientists of many different types. We shall tell the story through the eyes of some of its most significant contributors. Their biographies enliven the pages of our book. Science is a cumulative enterprise. Even Isaac Newton, one of the greatest scientific minds and not one customarily given to humility, wrote, quoting an idea ancient even in his time, that if he had seen further than others it was mainly because he was standing on the shoulders of his predecessors.16 And so it is with our contemporary understanding of neuromuscular physiology. That understanding rests on the painstaking work and insights of a multitude of thinkers and experimentalists of the past. Our book will not dwell on the sometimes overwhelming complexity and detail of 20th- and early-21st-century neuroscience, but will focus instead on the great challenge to ultimately overcome the old physiology of hollow nerves and subtle fluids—of, in short, the animal spirit doctrine—during the Early Modern period. It is at this time, during the 17th and 18th centuries, that the foundations of our modern understanding were laid. It is at this time that some of the greatest minds were active and some of the most intriguing scientific lives were lived. And it is late during this period that the mind breathed its last and instead began to transmit its commands and receive its information from the senses by way of that great 18th-century discovery—animal electricity. The structure of the book is shown in the Table of Contents. It is divided into five sections. The first discusses the part played by the animal spirit doctrine in antiquity; the second, its significance in the medical theories of the Middle Ages; the third, the beginning of critical questioning in the 17th century; the fourth, its slow replacement by alternatives in the 18th century; and the fifth, the transition to electricity. Throughout the book, a series of chronological tables and brief introductions ensure that readers are able to orient themselves within the larger historical context against which the narrative of the animal spirit doctrine, its rise, success, and fall, is told.

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Prologue Finally, a few words are in order about the title of our book. Should animal “spirit(s)” be written in the plural or the singular? There is no doubt that tracing the term to its origins in the ancient world indicates that we should use the singular form: “spirit.” The term was introduced in Greek antiquity, as we saw above, as “pneuma” (meaning wind, or breath) and from there was translated into Latin as “spiritus.” However, when the ancient medical texts began to be translated into the vernacular, and fresh texts began to be published during the Renaissance and Early Modern periods, the plural form was frequently used. René Descartes, for instance, writes of “les esprits animaux,” Thomas Willis maintains that the “Ancients” regarded the ventricles as a “the shop of the Animal Spirits,” and Francis Bacon writes that “opiates, and the like, banish the spirits.” There is a persistent inconsistency throughout this period. Animal spirit(s) is/are either thought of in “molar” terms, like oxygen or nitrogen or water, or in “molecular” terms, like (p.xiv) O2, N2, or H2O. In our book we shall attempt to use the etymologically correct singular form wherever possible, but when discussing authors who use the plural, such as Descartes, we shall necessarily use their chosen form. The term “animal” in our book’s title has also been a source of confusion. The 18th-century Anglo-Irish satirist Jonathan Swift writes “it is the opinion of choice virtuosi that the brain is only a crowd of little animals, but with teeth and claws extremely sharp, and therefore cling together in the contexture we behold, like the picture of Hobbes’s Leviathan, or like bees in perpendicular swarm upon a tree.”17 This is the “molecular” view of the spirits. But it also gives a radically incorrect view of the meaning of the term “animal” in “animal spirits.” “Anima,” as we noted at the beginning of this prologue, is the Latin translation of the Greek psyche, and both are related to the English word “soul.” So animal spirit or spirits have to do with the animating force that enlivens both animals and humans, and nothing to do with the notion of a “crowd of little animals” inhabiting the nervous system, as Jonathan Swift would have us, jokingly, believe. Enough of this pedantry. Let us now turn to the beginnings of our history in the first section of this book. We shall use the singular or plural form, spirit or spirits, as the context suggests and recognize that “animal,” in this context, refers to an animating principle, such as that found in animals and men, and has no other connection with the myriad animals studied by zoologists.18 Notes:

(2) “Paradigm change” and “paradigm shift” are the technical terms used by historian of science Thomas Kuhn (1962) for the substitution of a general and usually long-reigning and comprehensive theory or “worldview” by another of a fundamentally different nature. The paradigm shift outlined in this book took centuries to accomplish.

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Prologue (3) Zysk, 2007. (4) Kuriyama, 1995. (5) Liddell and Scott, 1897; Peters, 1967. (6) Anaximenes, at the beginning of the pre-Socratic tradition in the late sixth century BCE, writes that “our soul, being air, holds us together and controls us, so does wind (or breath) and air enclose the whole world” (Kirk and Raven, 1971, p. 158). (7) Crawley, 1909, p. 1. (8) Murray, 1924, XXII, 360. (9) Ibid., IX, 410. (10) Whether an individual called Homer ever existed is doubtful; the Homeridae were a lineage of poets claiming descent from Homer who made themselves responsible for reciting (and perhaps elaborating on) the Homeric poems. (11) Erwin Rhode reminds us that we should not rush too quickly to a belief that we understand the thought of Greek antiquity (Rhode, 1925). Ancient writings carry a whole penumbra of meaning that translation into a modern tongue cannot capture. We cannot do better than quote a passage from Rhode’s monograph to show how little the ancient thought-world maps onto the modern. “But how are we to think of this ‘Psyche,’” writes Rhode, “that unnoticed during the lifetime of the body, and only observable when it is ‘separated’ from the body, now glides off to join the multitude of its kind assembled in the murky regions of the invisible? Its name, like the names given to the ‘soul’ in many languages, marks it off as something airy and breath-like, revealing its presence in the breathing of the living man. It escapes out of the mouth—or out of the gaping wound of the dying—and now freed from its prison becomes, as the name well expresses it, an image (eidolon). On the borders of Hades Odysseus sees floating `the images of those that have toiled [on earth]’…[the psyche is] the body’s shadow-image, it survives the body and its vital powers.” It possesses no intellect, emotion, appetition, etc. yet remains invested with the full name of the deceased. Thus, continues Rhode, “According to the Homeric view, human beings exist twice over: once as an outward and visible shape, and again as an invisible ‘image’ which only gains its freedom in death. This, and nothing else, is the Psyche.” (12) Adkins, 1970, p. 15. (13) Onians, 1951. (14) Adkins, 1970, p. 17. Page 8 of 9

Prologue (15) Kirk and Raven, 1971, p. 94. (16) Letter to Robert Hooke, 1676; see Maury, 1992. (17) Swift, 1704, p. 34. (18) The Greek for animals is Zoa (ζωα), from which we derive zoo, zoology, etc.

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Introduction

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.5) Introduction The long story we are about to initiate refers to a scientific quest: understanding the basic process by which the nervous system of animals, including humans, is able to communicate almost instantaneously within itself and with the rest of the body. Today we refer to this process with the technical names “nerve impulse” or “action potential,” meaning a brief electrical alteration across the membrane of a nerve cell that propagates rapidly all along the fiber, from its beginning to the terminals. Neurologists can accurately measure the speed of this electrical wave in different nerves, and physiologists know its mechanisms in detail, i.e., the various membrane proteins involved, their fast reversible conformational changes to permit short inward and outward fluxes of electrical current in the nerve fiber, and how to block it temporarily with local anesthetics so that, for example, dental patients can endure the removal of a tooth with a minimum of pain, as never before in human history. Nevertheless, the notion that nerve impulses are electrical has been around for only about 200 years. Prior to this—from about the time when the Romans were just beginning to build an empire in the third century BCE (Before the Common Era), and up to about the date of the French Revolution near the end of the 18th century—pain, pleasure, and motor commands to muscles were all thought to be carried along the nerves by a tenuous fluid or “spirit.” And the root of this ancient idea is much older still, appearing formulated already in the writings of early Greek philosophers from over 25 centuries ago, most probably as an elaboration of prehistorical conceptions common in many primitive cultures.

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Introduction Overall, we have before us an immense trove of intelligent theorizing, partial agreements and disagreements, philosophical and religious disputes, scientific hypothesizing, and controversies about the “spirit” that for millennia was believed to mediate feelings and movements, even thinking in humans—that is, animae spiritus or the very spiritus of the anima, the soul—until systematic experimentation finally revealed its electrical nature. Our main goal in the first section of this book, therefore, will be to evoke how psyche, soma, and pneuma, the Greek words that were later on Latinized as anima, corpus, and spiritus, were first conceptualized in the various philosophical and medical schools that flourished in the ancient Western world. As it will be seen in Chapter 1, the earliest thinker who can be cited in relation to our topic is Thales, one of the “Seven Sages of Greece,” all of whom lived during the first half of the sixth century BCE. Those wise men were for the most part both shrewd rulers and politicians concerned mostly with legislation towards a fair and efficient government. Yet Thales was different from the other six sages in that he was driven to think more about the individual person and the natural world that we all inhabit. This wide-spectrum interest is reflected in that he is best remembered for two quite different contributions to human understanding: (1) having pointed out that the first duty of anyone striving for a good life should be to “know thyself,” and (2) predicting that a solar eclipse would occur in the year 585 BCE, as in fact it did. Perhaps more significantly at the time, Thales showed that utility could be obtained from the same training for keen observation and clever reflection that allowed him to know beforehand of that rare celestial occurrence. Indeed such abilities could also be put to practical use for doing good business. Thus, having correctly foreseen that a plentiful harvest of olives would take place in a certain year, he rented in advance all the olive presses available in town, so as to become the sole supplier when they would be needed. The astute plan paid off. Hence Thales, equally interested in man, the sun, and lucrative commerce, is often identified as the first Westerner to have practiced “philosophy” (i.e., love for knowledge). This our first philosopher was a citizen of Miletus, probably the busiest and wealthiest of many Greek colonies established around the Aegean Sea (see Fig. 1.2). Seated in Ionia on the Western coast of what today is Turkey, right at the crossroads of communication and trading between Asia Minor, Europe, and the north of Africa, the city offered numerous opportunities for prosperous entrepreneurs to consider new business options and for debating different views on all kinds of subjects. After all, as Thales demonstrated, knowledge could be profitable as well as interesting and elegant. Not surprisingly, other “lovers of knowledge” soon appeared, not only on the Milesian scene but in other neighboring Greek cities too.

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Introduction The penchant for philosophizing eventually spread throughout the periphery of the Greek world, going across the Aegean Sea and over a good part of the Mediterranean, from Ionia to the Greek western colonies established in southern Italy and Sicily. Philosophy finally made its way to Athens, the dominant city on mainland Greece. As a result of this wide spreading, the Greeks developed a unique taste for discussing and contrasting viewpoints about almost everything, from the best possible legislation to what the world is ultimately made of, and the most probable explanations for nature’s intricate behavior. Soul and body were among their many subjects of analysis, thereby giving rise to philosophically based medicine. Accordingly, our opening chapter examines how certain ideas about the soul and the body meandered through the geo-intellectual tangle that characterizes early science. Starting from the cities of Miletus and Ephesus in Ionia, (p.6) we will next visit Croton and Acragas in Italy and Sicily, respectively, and last we shall sail eastbound for resplendent Athens. Along the way we shall learn the reasons why a soul could be supposed to exist even in certain stones, about its close relation to air or breath (pneuma in Greek) and fire, or whether it rather combines the nature of these two elementary fluids, like a warm air endowed with intelligence. Disturbances of the normal amount of this pneuma within blood vessels, we shall be told by Hippocratic physicians, can be the cause of epilepsy and other serious neurological diseases. Most important of all, however, will be the controversial issue about the topographical distribution of the soul within the human body. Is it located mainly in the head, or in the chest near the heart? Or is it perhaps composed of various parts found in different places of the body? Or, if not localized, is it consubstantial with the whole functional structure of the body, the pneuma being in this case just its operative instrument? Some of the answers to these questions will come up in Chapter 2, which will first take us to Alexandria in Egypt, where a great center of Greek intellectual activity flourished while Athens slowly underwent a decline. Some leading Alexandrian physicians, who also were expert dissectors, concluded that the soul is located in the head, and that it is able to communicate with the sense organs and muscles through a specific kind of pneuma channeled along thin strings called neura. This scheme would be modified and expanded several centuries later by Galen, “the Prince of Physicians” and personal doctor to several Roman emperors, including Marcus Aurelius. Galen’s eclectically unified theory about human anatomy and physiology, enriched with ideas from many sources and having at its center a set of three pneumata or “spirits,” would become the most durable medical doctrine in antiquity, one that would still be entertained well into the Renaissance.

(p.7) Chronology

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Introduction

BCE (Before Common Era) (fl. = floruit) Thinkers

Context

585 Thales (fl.) 570 Anaxaminder (fl.) 546 Anaxamines (fl.) 535 Pythagoras (fl.) 509 Establishment of Roman Republic 494 Destruction of Miletus 490 Battle of Marathon 485 Parmenides (fl.) 480 Battles of Thermopylae and Salamis 479 Delian League established 475 Alcmaeon (fl.) 470 Socrates (b.)

470 Aeschylus (fl.)

465 Heraclitus (fl.)

465 Sophocles (fl.) 457 Pericles (fl.) 435 Phidias (fl.)

431 Empedocles (fl.)

431 First Peloponnesian War

430 Leucippus (fl.)

430 Plague in Athens

410 Democritus (fl.) 400 Hippocrates (fl.) 399 Execution of Socrates 380 Plato (fl.) 336 Aristotle founds Lyceum 334 Foundation of Alexandria 323 Death of Alexander 322 Death of Aristotle 310 Zeno founds Stoic school in Athens

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Introduction

BCE (Before Common Era) (fl. = floruit) Thinkers

Context

307 Epicurus founds Epicurean school in Athens c. 300 Foundation of Alexandrian Museum & Library 300 Herophilus (fl.) 265 Archimedes (fl.) 270 Erasistratus (fl.) 146 Rome sacks Carthage 44 Assassination of Julius Caesar 40 Lucretius: De rerum naturae 64 Seneca: Questiones naturalis 77 Pliny: Historia naturalis 79 Destruction of Pompeii c. 80 Dioscorides: Materia medica 190 Claudius Galen (fl.) 195 Tertullian (fl.) 350 Posidonius of Byzantium develops a ventricular psychology c. 390 Nemesius: De natura hominis 395 Augustine made Bishop of Hippo 410 Sack of Rome by the Visigoths 426 Augustine: De civitate dei 430 Death of Augustine 476 Romulus Augustulus, last Western Roman Emperor, forced to abdicate (p.8)

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Psyche and Soma

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Psyche and Soma C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0001

Abstract and Keywords This chapter studies the ancient Greeks' understanding of the soul and body, as well as the relationship between the two. It discusses a set of basic notions, including movement and keeping the body together against disintegration, and the heart. It studies the start of scientific thought, from the pre-Socratic philosophers until the height of classic Greek philosophy. It focuses on the works of Plato and Aristotle and outlines the development of early Greek conceptions about the soul and body. It then examines how these notions influenced the birth of scientific medicine. This chapter concludes with a review of the teachings on the soul and body by some representatives of Epicureanism and Stoicism, which are two opposing philosophical-scientific schools that prospered from the postAristotelian period until the rise of the Roman Empire. Keywords:   soul, body, heart, scientific thought, Plato, Aristotle, classic Greek philosophy, pre-Socratic philosophers, Epicureanism, Stoicism

As our soul, being air, holds us together, so do breath and air surround the whole universe. Anaximenes, c. 550 BCE (trans. Freeman, 1996, p. 19)

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Psyche and Soma To break into our subject we first need to have some grasp of what the ancient Greeks understood by soul and body, and what they thought about the relationship between these two traditional complementary components of humans and animals. Needless to say, the topic represented no less a battle of concepts and beliefs then than it does still today. Even so, a few common issues can be identified on which everyone basically agreed. Soul, the entity that enlivens the body, is perhaps easier to define by considering the opposite of life. For death is clearly marked by absences, by a sudden leaving of several properties present in the living body. The three most immediately obvious losses are, in order of departure, movement, breathing, and warmth in homeothermal animals. At a later stage the absence of the soul leads to a fourth destitution, that of the body’s integrity. Accordingly, the soul is somehow responsible for moving the body, including the respiratory movements, as well as for keeping it warm and united as a whole. What happens to the soul after death is an even more debated issue, but of no concern to us here. From the scientific point of view, faith in an afterlife may be regarded as a cultural expression of the instinct for survival present in all animals. And the study of animal instincts belongs to ethology, a fascinating field of biology but outside our present inquiry. In the following sections of this chapter, therefore, we shall focus on the above set of basic notions—movement, air and breath, warmth, and keeping the body together against disintegration. In addition we shall often refer to the heart, for the heartbeat also ceases at the instant of death, as well as to the blood, for a serious hemorrhage can by itself lead to death.1 With these main targets in mind, the initial stage of our journey through time will take us from the dawn of scientific thought, represented by the so-called pre-Socratic philosophers, to the height of classic Greek philosophy, personified by Plato and Aristotle (Fig. 1.1). This 300-year odyssey involved a gradual convergence, not only intellectual but also geographical (Fig. 1.2). Ideas grew and flowed from the periphery of the Greek civilization in the sixth century BCE, which was spread over the coasts of what are today’s Turkey, Italy and Sicily, up to its cultural and political center in Athens during the fourth century BCE. We shall first trace the sinuous development of early Greek conceptions about soul and body, and next examine how these notions influenced the birth of scientific medicine, ultimately to bring us to the origin of the profound dichotomy that has marked Western knowledge since then. This is discussed as the chapter closes with a broad review of the teachings on these matters by some representatives of Stoicism and Epicureanism, the two conflicting philosophical-scientific schools that flourished from the immediate post-Aristotelian period to the rise of the Roman Empire.

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Psyche and Soma Now, when we decide to go back so much in time and cognitive evolution, we must also be ready to learn a way of thinking that is equally far away and totally different from our own.2 This difficulty is further combined with the lack of proper documentation, because with the exception of Plato’s Dialogues, plus the Aristotelian treatises and certain works from a few others, the numerous original writings of those early thinkers did not survive antiquity. Therefore, the dispersed fragments now available to us about them—usually second- or thirdhand references—include, among supposedly verbatim quotations, personal comments from readings of lost originals, and in some cases even misleading imitations. Nevertheless, the exercise of trying to discover the partly hidden foundations of our scientific culture is exciting, interesting, and instructive. So let us now move back in time for 26 centuries and attempt to understand how those ancient intellectuals, in their own personal and tentative ways, struggled to offer reasoned accounts of some fundamental phenomena shown by the bodies of humans and animals. (p.10)

Figure 1.1: Classic Greek philosophy developed for about 300 years, from the earliest pre-Socratic thinkers in the sixth century BCE down to the establishment of the major schools in Athens during the fourth century. New trends that derived from these precedents then continued through the Hellenistic period and into the Roman Empire. The figure shows only the lifetimes of the authors mentioned in the present chapter.

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Psyche and Soma (p.11) Soul Once a handful of uncommonly curious Greek minds started to find the old mythologies unsatisfactory, explanations about how the world might really be constituted multiplied rapidly.3 Soul and body—psyche and soma—remained always as central themes of such speculations. Thus psyche appears already in the scarce data still conserved about the ideas of the very first Western philosopher whom we know something about—Thales, who lived in the sixth century BCE in

Figure 1.2: Western philosophy was born in Greek colonies established on the coast of the Anatolian peninsula (today Turkey) at the Eastern end of the Mediterranean Sea, then migrated westbound to Greek

cities in the south of the Italian peninsula the cosmopolitan and and Sicily, and finally flourished in prosperous city of Miletus, on Athens, the cultural and political center the western coast of the of the Greek world in the fourth century Anatolian peninsula. BCE. Significantly, however, the term psyche does not allude in this early instance to feelings, consciousness, existence, transcendence, or an afterlife. In other words, the noun is not applied here to what we today generally understand as “soul,” or to a subject belonging minimally in the field of philosophy or psychology. Moreover, it does not refer even to human affairs or at least to animals. It simply corresponds to a hypothesis to explain an amazing property of a mineral—the power to induce movement, inherent in the lodestone or magnetite. This peculiar kind of rock—abundant in the region of Magnesia in eastern Greece, from where its name derives (magnitis lithos)—thrusts itself toward iron-containing objects that are placed nearby, or pulls them toward itself until direct contact is established. Still more strikingly, the stone is able to communicate this strange virtue to the metal while the contact persists, so that other iron objects will be attracted to the one in contact with magnetite. This phenomenon must have been especially intriguing in Thales’ time, in the late Iron Age, when metallurgic technology was a key issue for the battlefield and elsewhere. The explanation that he offered for this enigmatic property, according to Aristotle’s account based in turn on testimonies he heard transmitted from older sources, is that the lodestone has soul: “Thales, too, to judge from what is recorded about him seems to have held soul to be a motive force, since he said that the magnet has a soul because it moves the iron.”4 Page 4 of 47

Psyche and Soma We may suppose that this explanation was not limited to just the lodestone, but that “soul” was for Thales the motive power behind all dynamism in nature. This is probably the reason behind another of his famous statements—that “all things are full of gods.”5 Accordingly, the immortals were not restricted to Mount Olympus, busying themselves with their divine quarrels or searching for goodlooking mortals to seduce. Instead, the gods would be intermingled in the basic substance of everything, which Thales concluded to be water. Few of Thales’ immediate successors as philosophers accepted his view that water is the fundamental material principle of the world, but all of them associated the soul with their own alternative choices. Thus Anaximenes (c. 585– 525 BCE), also a citizen of Miletus, held that all the requisites that such a basic principle should possess—inexhaustible abundance, self-movement, and interconvertibility with other things—are met by the very substance of the soul. Air (aer), immortal like the gods, and just like them invisible and powerful, which by its own impulse flows as wind (pneuma), is—Anaximenes argued—the soul of the whole cosmos. Not only can it impart its own motion to other things but also, just as the individual animal soul keeps the body united (i.e., by preventing its decomposition) until the moment of death, so too air preserves the unity of the world. In Anaximenes’ words: “As our soul [psyche], being air [aer], hold us together, so do breath [pneuma] and air surround the whole universe.”6 Air in movement is thus breath or pneuma with the holding power of life. It is therefore with Anaximenes, apparently, that the word pneuma started its long trek across Western thought, although the credit for being the first to declare that “the soul [psyche] is breath [pneuma]” has been attributed also to his slightly younger contemporary, Xenophanes of Colofon (c. 570–480 BCE).7 In any event the actual term appears to have originated in the middle to late sixth century BCE, though the root “pnoe” or “pnoie,” denoting breathing, is found already in the eighth-century BCE Homeric poems,8 and remains in use today for current nouns such as “pneumonia,” “pneumatic,” and “apnea.”

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Psyche and Soma A similar concept was expressed in different words by Heraclitus (c. 540–475 BCE), who lived in Ephesus not far to the north from Miletus. Considering that everything in the world is in a state of perpetual flux, as is the case with fire, Heraclitus maintained that the latter should be the fundamental principle of all things. Here the term “fire” includes, but is not necessarily limited to, actual flames. It has a much wider connotation that refers to the primal heat, a mysterious agency that can pass from one body to another like an emanation. Hence soul must also ultimately be, like everything else, this “‘warm exhalation’…most incorporeal and in ceaseless flux.”9 Yet in living bodies, said Heraclitus, the warm exhalation is found in a sort of dynamic equilibrium with water—that is, as a kind of steam or vapor. Therefore, as soon as the warm exhalation leaves a person or animal due to any cause, the vapor reduces to water and then the body, up to that point still alive, becomes inert and thereafter disintegrates. In turn, the essentially igneous (p.12) soul becomes reborn when the body dies, since in a way the soul originally underwent a certain wetting, something akin to half-dying, when installed in a body. For, according to Heraclitus, “to souls, it is death to become water,”10 and conversely, “A dry soul is the wisest and best.”11 This idea that the soul is somehow degraded by its temporary association with a body, an undesirable but obligate companion in this worldly life, was to project a long shadow throughout the following centuries, reaching up to our own time. While the uncomfortable binding persists, Heraclitus believed, any further hydration of the soul should be prevented. Fittingly, from what little is known about him as a person, Heraclitus’ contemporaries must have been certain that his soul was the driest around. Ironically, however, fate disposed that his body would suffer from the opposite quality if, as probably ill-meaning gossip had it, dropsy plagued him in old age.12 Spontaneous self-movement also appears to have been ascribed to the soul by Pythagoras (c. 570–490 BCE), who due to political circumstances preferred to flee westbound from his native island of Samos, just west of Miletus and Ephesus in the Aegean Sea, and settled finally at Croton, in southern Italy. Evidently he did not like any of the existing hypotheses about the basic principle of nature, all of which shared the common idea that everything is made of a single constituent as coarse as a substance—be it water, air, fire, or a boundless stuff (apeiron) proposed by Anaximander, another early philosopher who was next in line to Thales.

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Psyche and Soma The true secret of the cosmos, Pythagoras reasoned, should rather consist of exact and inalterable principles beyond the circumstantial variations of matter. Along this path of thought, he concluded that everything should be intelligible in numerical terms. Moreover, he taught that the numbers themselves constitute the actual substrate of the universe, for their powers are indeed impressive in fields as varied as predicting the movements of the heavenly bodies, calculating exact dimensions, or tuning up the sounds of a lyre. As we shall see below, this perspective was to exert a decisive influence on a whole branch of Western philosophy—Platonism—so a few more facts about the Pythagorean School are worth including here. Unfortunately Pythagoras strove to keep his teachings available to only a limited cohort of disciples, and therefore did not write, relying instead on transmission by way of mouth to selected ears at his exclusive school in Croton. Nevertheless, according to Alexander Polyhistor, a first-century CE historian of philosophy, Pythagorean speculation about just how the numbers could be the source of everything went as follows: The principle of all things is the monad or unit;…from the monad and the undefined dyad [i.e., the “two”] spring numbers; from numbers, points; from points, lines; from lines, plane figures; from plane figures, solid figures; from solid figures, sensible bodies, the elements of which are four, fire, water, earth, and air.13 Yet according to Aristotle, when it came to the soul the followers of Pythagoras used as an analogy the dust particles that can be seen suspended in air when a beam of light passes through a darkened space: “some of them [the Pythagoreans] declared the motes in air, others what moved them, to be soul. These motes were referred to because they are seen always in movement, even in a complete calm.”14 Any one of these two Pythagorean versions of soul must be reconciled with another of their central postulates—that following death the soul starts looking for a new suitable body to inhabit, until that merciful day when the successive cycles of reincarnation end after proper purification is reached. The only way for abbreviating the number of these painful cycles was to lead a virtuous life, and to this end nothing could be better than observing the precepts set by Pythagoras himself.

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Psyche and Soma Paramount among these directives is that one should at least be prudent enough to follow a strict vegetarian diet, because by definition souls migrate only between “animated” bodies, and therefore eating anything that had sometime moved by itself might interfere with the process. Accordingly, the Pythagoreans adopted the moral practice of consuming only foods of vegetable origin, with the notable exception of beans, which were absolutely forbidden “because they are flatulent [pneumatodeis] and partake most of the breath of life [psychikon].”15 Why the seeds of this leguminous plant are endowed with such a special distinction is open to conjectures. At any rate the transmigration of the souls or “metempsychosis,” a concept imported from the East and summarized by Plato,16 the most relevant champion and further developer of Pythagoreanism (see below), is beyond our present interest. We must suppose, however, that every time when a soul reincarnates, it manages to handle its new body just like it did with the previous one.17 A harder decision is whether we should examine here the singular position of the school founded by Parmenides (c. 515–445 BCE) in Elea, also in southern Italy. These important philosophers had very little to say about the soul or any other motive power of the body, and for a good reason. They seriously claimed that all movement is impossible from a strictly rational viewpoint, and hence cannot exist. Any evidence to the contrary is but a product of our deceptive sensations or imagination. Take for example Zeno’s (c. 495–430 BCE) well-known paradox of the almost invincible mythological warrior Achilles pursuing a humble tortoise. According to Eleatic philosophy the audacious hero would never be able to overtake the animal, because there is no valid way of denying that the latter would always be a bit ahead of its pursuer if both kept moving all the time.18 In fact, for Zeno such a race would have been impossible to start with, (p.13) because he reportedly believed that “A moving body moves neither where it is nor where it is not.”19 Presented with this theoretical impossibility concerning the existence of motion, our best option is perhaps that of the Cynic philosopher Diogenes of Sinope (fl. 350—320 BCE), who, upon hearing about such problem, just “got up and walked about.”20 So, having already considered some early Greek concepts of the soul, let us now move on and review what some of the early philosophers thought about its counterpart, the body itself.

Body

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Psyche and Soma Along with the soul, the body was also a matter of deep reflection among the Pythagoreans, and two figures closely related to this sect are of special interest to us here. A physician named Alcmaeon (fifth century BCE) who lived in Croton, right where the school of Pythagoras was founded, shared the belief that the soul is immortal and in continuous motion, although rather than dust particles dancing in mid-air he preferred the more dignified analogy of the heavenly bodies.21 He is also credited with having acquired at least some knowledge about the internal construction of the body, though almost certainly not by dissecting human corpses as is occasionally surmised.22 A seldom-noted fact is that, since he is known to have written the results of his own investigations for others to read, Alcmaeon seems to have been the first researcher to “publish” scientific work on biomedical topics. Two of Alcmaeon’s ideas concerning the body are of significance for our present purpose. First, he reached the conclusion that the encephalon must be the ruling center of the body. Whatever his methods, according to Aristotle’s successor Theophrastus, Alcmaeon realized that “all the senses are connected in some way with the brain, consequently they are incapable of action if the brain is disturbed or shifts its position, for this organ stops up the passages through which the senses act.”23 The actual meaning of the Greek word “poroi” translated as “passages” in this quotation has been controversial. Alcmaeon seems to have dissected animal eyes and observed the optic nerve, so in this instance at least his poroi might have been a reference to the optic nerves. He also seems to have associated poroi with the other senses, excluding touch, again possibly alluding to structures later identified as nerves. Still, nerves, tendons, and blood vessels seem to have been inadequately distinguished from each other at this moment in time, much as was also the case with the ancient Egyptians, who used the word “metu” for passages to and from the ruling heart. Hence, with only sketchy records and sometimes questionable sources to draw from, it remains possible that Alcmaeon’s poroi could have been a generic term that included more than just the nerves as hollow passages for communication.24 In any event, the excerpt quoted by Theophrastus leaves no doubt that Alcmaeon was aware that the nostrils and the ears are continuous with hollow spaces that penetrate into the head toward the brain (i.e., the nasal cavity and the external auditory canal, respectively). Further, in the case of smelling, he is explicit that perception is associated “with the act of respiration when one draws up the breath [pneuma] to the brain.”23 The most puzzling question, however, is whether this notion was also applied to the optic nerves that emerge conspicuously from the back of the eyeballs, for other sources from antiquity report a lumen in them—likely the central artery of the retina.

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Psyche and Soma Hence, the available records allow us to conclude only that Alcmaeon apparently viewed sensory perception as mediated by pneuma contained within the animal or human bodies. If so, this would be the first recorded instance of pneuma being regarded as somehow involved in the transmission of physiological information. Stretching this guess a little further, Alcmaeon might have been alluding to specific pathways or conduits, possibly other than the blood vessels favored for this function by nearly everybody else at the time (see below). But there are complications even with these tentative interpretations, because in Alcmaeon’s physiological system consciousness, and thus presumably sensory perception as well, is apparently dependent upon certain movements of the blood, rather than upon pneuma as it might be expected. According to such a view—the second of interest for us here regarding Alcmaeon—withdrawal of the blood into the vessels would cause sleep, whereas its flowing back would produce awakening, with permanent blood withdrawal being tantamount to death.25 The ruling center of the body and blood movements were discussed also by a somewhat younger contemporary of Alcmaeon, the colorful Sicilian politician, philosopher, healer. and poet Empedocles of Acragas (c. 490–430 BCE), who took an eclectic position in the ongoing debate about the fundamental substance of everything. He taught that all of the main theories about the first principle comprising all things were partly right, for there are in fact four “roots” of everything: water, air, fire, and earth, a tetrad long known in later ages as “the four elements.” Each of these is soul in a way, and all of them together also constitute soul.26 Mixtures of the same four basic substances in different ratios also make up the four main components of the body—blood, bone, flesh, and sinew or neuron.27 This latter term was apparently applied to all kinds of whitish cords and ligaments found everywhere inside the body, while “flesh” was a generic expression that corresponds to every soft part. According to Empedocles the heart, “nourished in the seas of blood which courses in two opposite directions: this is the place where is found for the most part what men call (p.14) thought; for the blood round the heart is thought in mankind.”28 His opinion was thus different from Alcmaeon’s, who viewed the encephalon instead of the heart as the supreme organ in the body.

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Psyche and Soma Yet Empedocles too found a purpose for the movements of the blood, though not in relation to sleep and awakening or death. Instead they drive respiration, for the motion of the blood is rhythmic like that of the waves on the beaches: it flows through the vessels from the inner parts of the body toward the surface, and then retreats inward again.29 These blood movements, in turn, cause inhalation and exhalation of air, though not only through nose and mouth but apparently also through the skin pores. Tiny tubules too narrow to admit any blood, but continuous with the wider vessels, reach up to the surface of the body and terminate at the pores. Accordingly, every withdrawal of the blood towards the interior of the body results in a rush of air sucked through the pores into the tubules, just like an egress of air through the same tiny pipes and outlets will follow as the blood expands out again. The extant fragments of Empedocles’ poems say nothing about what drives the rhythmic surges and retractions of the blood through the vessels, but they do explain the physical principle behind the associated inhalation and exhalation of air. He illustrated the phenomenon by the famous simile of the water-thief or clepsydra, a handy instrument used in antiquity to transfer water, wine, or other liquids between containers by the same simple physical principle still at work in modern pipettes in many laboratories (Fig. 1.3). The important point here is that air, though invisible and impalpable, does occupy a volume in space. Therefore, if a tube is full of air that is somehow trapped within, a liquid cannot get in before the air is let to escape; and by the same token, if the tube is full of a liquid, this will only be released if air is allowed to get in. The alternate flows of air and liquid within a narrow duct are thus necessarily coupled. Anaxagoras of Clazomenae (c. 500–430 BCE), an heir of the school started by Anaximenes in Miletus, also recognized that invisible air is a body occupying space. He is remembered as the herald who, invited to Athens by the political leader Pericles (c. 495–429 BCE), first took to the fast-rising city the new scientific outlook and fashion of philosophizing invented in the eastern Greek colonies. Unfortunately the Athenians were then still far from accepting such suspicious novelties, so the eminent guest was later on expelled in a hurry under the accusation of spreading impious ideas. Apart from experiments with clepsydras,30 equivalent to the example used by Empedocles, Anaxagoras made use of demonstrations with wineskins.31 If the spigot is plugged in tight after all the wine is allowed to drain out, a wineskin will nevertheless resist compression because the apparently empty bag still contains something, i.e., space-filling air.

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Psyche and Soma

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Psyche and Soma Soul as Intelligent Warm Air Within the Body

Figure 1.3: A modern laboratory pipette works for the same purpose and on the same principle as the ancient water-thief or clepsydra, which Empedocles used as a metaphor to illustrate a supposed direct coupling of respiration with the movements of the blood.

We have so far examined how several of the earliest known philosophers in the Greek world floated up some interesting and partly connected or overlapping ideas about soul and body. Soul could be a binding and moving power with a fluid nature capable of permeating through solid objects, just like a magnetic force, air, or heat do. Air, however, though much thinner than any liquid, still occupies a volume and can only (p.15) pass through open passages.32 Accordingly, air must flow through an animal body along conduits similar or perhaps even the same as those that also carry blood and sensations directionally, in relation to either the heart or the encephalon; and at least some of those fluxes might be associated with sleep or even death. A reasonable compromise among these various notions was then explicitly put forward by a younger follower of Anaximenes, the philosopher Diogenes of Apollonia (c. 460– 400 BCE). First he stated the main tenets of his philosophical position in this regard: And it seems to me that that which has Intelligence is that which is called Air by mankind; and further, that by this, all creatures are guided, and that it rules everything; for this in itself seems to me to be God and to reach everywhere and to arrange everything and to be in everything. And there is nothing which has no share of it; but the share of each thing is not the same as that of any other, but on the contrary there are many forms both of the Air itself and of Intelligence; for it is manifold in form: hotter and colder and dryer and wetter and more stationary or having a swifter motion; and there are many other differences inherent in it and infinite [forms] of savor and color.33 Specific conclusions follow immediately: Also in all animals the Soul is the same thing, [namely] Air, warmer than that outside in which we are, but much colder than that nearer the sun. This degree of warmth is not the same in any of the animals (and indeed, it is not the same among different human beings), but it differs, not greatly, but so as to be similar.…all things live, see and hear by the same thing [Air], and all have the rest of Intelligence also from the same.

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Psyche and Soma Consequently Diogenes, who most probably was a physician, ventured in search of air pathways within the human body, perhaps in the hope of learning how to treat patients in a more effective way. Since he, like Empedocles and almost everybody else at the time, believed that air and blood flowed through the same ducts, the result was the first relatively accurate description of the vascular system, known to us today because Aristotle quoted it in its entirety.34 Diogenes’ influence is clearly evident in some of the earliest documents of the proto-scientific medical school associated with the name of his contemporary Hippocrates of Cos (460–377 BCE), known as the “Father of Medicine” (Fig. 1.4).35 Thus, for example, the manuscript titled On Breaths states that Wind [pneuma] in bodies is called breath, outside bodies it is called air [aer]. It is the most powerful of all and in all…[since when] much air flows violently, trees are torn up by the roots through the force of the wind, the sea swells into waves, and vessels of vast bulk are tossed about.36

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Psyche and Soma Furthermore, wind is also the most critical of the three kinds of food that nourish the bodies of mortal beings, for “while a man can be deprived of everything else, both food and drink, for two, three, or more days, and live, yet if the wind [pneuma] passages into the body be cut off he will die in a brief part of a day.”37 Inhaled air or pneuma, as Diogenes concluded, is also the source of intelligence according to some

Figure 1.4: Hippocrates of Cos (460–377 BCE), the “Father of Medicine,” founded an innovative school in which diagnosis and treatment of patients were carried out according to general natural (“physical”) principles, much like the early Greek philosophers attempted to explain the world from simple fundamental ideas independent from religious views. Thus shamans and healers were gradually substituted by “physicians” in Greek cities, and a new profession was born. (Sculptured imaginary portrait by unknown artist, now exhibited at the Pushkin Museum, Moscow; Wellcome Library, London, cat. M0000770.)

Hippocratic authors. Thus, in another famous treatise—On the Sacred Disease, (p.16) a discourse on epilepsy—we read that “when a man draws breath [pneuma] into himself, the air first reaches the brain,” where it leaves “its quintessence, and all that it has of intelligence and sense.”38 Only then is the airy current distributed to the whole body through the vessels. For “If it reached the body first and the brain afterwards,” the unknown author goes on, “it would leave discernment in the flesh and the veins, and reach the brain hot, and not pure but mixed with the humor from flesh and blood, so as to have lost its perfect nature.” Because pneuma carries intelligence, sensitivity, and movement to all members of the body, any alteration in its distribution is bound to result in serious health problems. This is what happens, for instance, when an abnormal discharge of cold phlegm descends from the head and chills the blood, which in turn blocks the vessels and hampers the normal flow of pneuma. Deprived of such vital and intelligent nourishment, “the patient is rendered speechless and senseless. The hands are paralyzed and twisted when the blood is still.”39 In other words, both sensory input and motor coordination are totally upset in a full-blown epileptic seizure. Another Hippocratic writer the author of On Breaths, held a converse explanation: an excess of pneuma in the vessels would hinder the blood flow and therefore make this uneven, a condition that then causes “all kinds of irregularities.”40 Still worse: when the “breaths,” instead of running normally within the vessels get extravasated and “pass through the flesh and puff it up,” the affected body parts could lose feeling and the whole body might become affected with apoplexy if the spillage is copious.41 Page 15 of 47

Psyche and Soma Little doubt existed at the time, therefore, that breath or pneuma flows throughout the body via vessels that also carry blood; and, even more importantly, that pneuma mediates all internal communication and the proper functioning of every bodily part. The practical significance of this theoretical concept for Western ancient medicine can hardly be exaggerated. In terms of Diogenes’ philosophical viewpoint it meant, of course, that the “intelligent” (i.e., appropriate) behavior of the body is directly conducted by the soul, which consists of the same principle governing everything else, namely aer.

Intrusion of a Skeptical Humanist Despite its general acceptance, however, the above explanation was found quite unsatisfactory by another famous contemporary of Diogenes and Hippocrates, a former pupil of Anaxagoras destined to become an icon of Western philosophy— Socrates (470–399 BCE; Fig. 1.5). Recalling his days as a beginner in philosophy, Socrates confessed to his younger friends and disciples while waiting in an Athenian prison to be executed that evening: I was glad to think that I had found in Anaxagoras a teacher about the cause of things after my own heart, and that he would tell me, first, whether the earth is flat or

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Psyche and Soma round, and then would Figure 1.5: Socrates (470–399 BCE), a explain why it is so of central figure in classic Greek philosophy, necessity, saying which is who shifted the focus of enquiry from the better, and that it was better broad investigations of his predecessors to be so.…I never thought about nature in general to probing more that Anaxagoras, who said about human interests and behavior in that those things were particular. (Sculptured imaginary portrait directed by Mind, would bring in any other cause for based on written contemporary them than that it was best descriptions, by L. Paredes, 1855, for them to be as they are.… Mexico; photograph by courtesy of Ana This wonderful hope was M. Guardia from a copy privately owned dashed as I went on reading by this chapter’s author.) and saw that the man made no use of Mind, nor gave it any responsibility for the management of things, but mentioned as causes air and ether and water and many other strange things. That seemed to me much like saying that Socrates’ actions are all due to his mind, and then in trying to tell the causes of everything I do, to say that the reason that I am sitting here is because my body consists of bones and sinews, because the bones are hard and are separated by joints, that the sinews are such as to contract and relax, that they surround the bones along with flesh and skin which hold them together, then as the bones are hanging in their sockets, the relaxation and contraction of the sinews enable me to bend my limbs, and that is the cause of my sitting here with my limbs bent.42

(p.17) Socrates’ deep disappointment can be understood. The cause for his being seated there awaiting death was a biased trial under the accusation of corrupting the youth. He brilliantly confronted his prosecutors in public, though unfortunately to no avail, and then accepted the sentence only because in his opinion the jury was legal and every good citizen should support the law of his country, no matter what.

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Psyche and Soma Socrates was a moral and dialectical genius who, in contrast to most of his predecessors, never wrote a single word about his doctrine and never showed a hint of wanting to create a “school.” Even in his last minutes, when asked about how he wanted his followers to continue the crusade started by him, his answer was merely the request that they should take care of themselves. At heart, he probably believed it was pointless and risky for them to go on along the same path he trod. The whole of Athens had been his student body for years and, in view of the condemnation, the results could hardly be called a success. In this he shared the failure of Anaxagoras, though, contrary to his philosophically disappointing mentor, Socrates refused the opportunity of escaping to safety. And yet eventually his teachings, validated in the first place by his own personal integrity, were the starting point for several new philosophical schools. The most influential of them was the Academy founded by a close Athenian pupil, whose name was apparently Aristocles but who is better remembered as Plato (428– 348 BCE; Fig. 1.6), a nickname he reportedly received either because of his wide shoulders or because of his broad writing style.

Plato’s Academy Like others who frequently enjoyed the instructive and amusing company of Socrates, Plato deeply resented the unfair destiny given to his old friend, and so decided to get into politics with an aim to change the perverse establishment. Nevertheless, when his aspirations and repeated attempts in this arena were frustrated, but while still convinced that only philosophers can make good governments, he resolved to promote the novel thinking of his victimized teacher. In view of the considerable achievements obtained by the Pythagorean sect, Plato sought to take this as a model and created a formal new school in a suburban park called “Gardens of Academos,” in memory of a hero of that name. The institution came therefore to be known as “the Academy” and started to operate in about 387 BCE. Except for the strong mystical flavor, it followed as much as possible the precedents set by Pythagoras at Croton, from curriculum content to the acceptance of selected female students. Preference was given to branches of knowledge that deal with what is forever perfect and true, like mathematics, geometry, astronomy, and musical harmony. However, special attention also was placed on matters that forever will be prone to imperfection and falsehood, like politics. The instructional method was generally in vintage Socratic fashion—that is, through strictly ordered conversations during healthy and well-wined dinners, though formal lectures and seminars were common too. Plato himself wrote what amounts to textbooks in the form of Dialogues—that is, as narratives of juicy thematic discussions that had allegedly happened, usually with Socrates as

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Psyche and Soma the protagonist. Among the few exceptions to this pattern is a lengthy lecture on the origin, structure, and inner workings of the universe, presented by a supposedly prominent Pythagorean physician, Timaeus of Locrii. As it might be expected from a representative of the famous school at Croton, the contents of this dialogue—for the most part really a monologue—are based on pure mathematical lore. Thus, for example, the four elements are identified with the so-called “Platonic solids” or regular polyhedrons (Fig. 1.7). We are not asked to believe everything mentioned there, since the speaker insists once and again throughout his talk that all he is saying should be regarded only as the most probable account, rather than as a description of demonstrated facts. Nevertheless, in contrast to most of Plato’s Dialogues, neither Socrates nor any one else attending the lecture interrupts the exposition to question anything.

The Timaeus occupies a special place in the transmission of scientific ideas as endorsed by Plato and taught at the (p.18)

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Figure 1.6: Plato (428–348 BCE), Socrates’ most influential pupil and mentor to Aristotle, established the first formal school of philosophy known in Western civilization, the Academy, mostly on the model of a mystical sect founded much earlier by Pythagoras but along the ideas and interest lines set out by Socrates. Plato is also the author of the first extant body of philosophical writings in the Western world, the Dialogues, which initiated a still continuing tradition. (Line engraving by L. Vorsterman after an original imaginary portrait painted by P. Rubens; Wellcome Library, London, cat. V0004701.)

Psyche and Soma Academy during the Golden Age of Figure 1.7: The “Platonic solids,” regular ancient Greek culture, the polyhedrons that according to the resplendent fourth century BCE. Timaeus (53a–54d) represent the four Later on it would be the single one elements—fire (tetrahedron), air of Plato’s works known in the West (octahedron), water (icosahedron), and during the Middle Ages, though earth (hexahedron or cube). The regular only in incomplete versions thanks polygons that constitute the faces of to partial translations into Latin by some Christian authors. It these bodies can all be ultimately remained a highly influential book constructed from simple right-angled up into the Renaissance and triangles, a fact used to explain why the beyond, being widely read by elements are in principle supposedly college students still today. The interconvertible with each other. (Image distinguished 20th-century of 3D digital constructions by courtesy of mathematician Alfred Whitehead Rafael Marmolejo, Mexico.) once remarked that Isaac Newton (1643–1727) would have been quite surprised by the astonishing discoveries of modern physics, whereas Plato would probably have expected them.

In the following paragraphs, in which the reader will hopefully keep in mind our warning about being prepared for non-conventional (by today’s standards) reasoning, we shall briefly review what Plato had to say about matters relevant to our present subject, beginning with his concept of a tripartite soul.

A Tripartite Soul Upon the premise that the only way of ordering a whole so that everything results as good as possible is by means of intelligence, which can only exist in soul, Timaeus de Locrii recounts that the creator “put intelligence in soul, and soul in body, and so he constructed the universe…as a truly living thing, endowed with soul and intelligence.”43 Such universal soul was built from a complex mixture of “Being,” “Same” and “Different,” which was then cut and pasted according to specific ratios that produced intervals in a certain numerical sequence. The resulting compound was next sliced into bands that were finally fashioned as seven concentric circles with various motions.44 Within this numerically and geometrically arranged framework the creator fitted “all that is corporeal” to complete the universe.

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Psyche and Soma Necessarily, the above original mixture prepared for fashioning the universal soul “was eventually completely used up,” but some second- and third-grade residues of the same ingredients were then used to create the immortal human soul.45 Next the creator commanded his offspring, the lesser gods, to build an appropriate container for this imperfect soul. Inexperienced as they were in the process of creation, these gods initially lodged the imperfect soul within a simple ball—the future head—so that it would resemble the disposition of the universal soul in relation to the round shape of the universe. It soon became evident, however, that while the universe can always stay in place because it has nowhere to go, humans have the practical need of transporting themselves about their surroundings. Hence, the primitive human ball was endowed with arms and legs so that it could move around, and also with eyes so that it could avoid obstacles along its way, as well as with ears, and so on.46 Managing these additions demanded, in turn, providing the ensemble with two supplementary mortal souls.47 One of these, characterized by passion, courage, and boldness, was placed in the chest together with a heart, and separated from the immortal soul by a narrow passage—the neck—to act as a restrictive boundary. The second mortal soul, a nasty aggregate of unruly appetites, was relegated to the abdomen, where it was associated with the liver, and separated from the other two by an even more restrictive partition, the midriff or diaphragm. Since all three parts of the human soul need to act in a coordinated manner, a sort of continuous linking connection was established between them by means of a special substance called “marrow.”48 This was constituted from stuff having the qualities of being truly elemental and perfectly rational—that is, “primary triangles” like those into which the faces of the polyhedrons corresponding to fire, water, air, and earth can ultimately be divided. The top part of the marrow was named “brain” and shaped round in order to fill up the roughly spherical head; the rest was stretched out like an elongated cord so that it could reach down to the lower trunk, with branches that extend from there throughout the limbs. The three souls were then implanted in this marrow, which binds them together and anchors the whole to the body. We are left to guess whether the two lower souls, found in the chest and the abdomen as mentioned above, are just linked to the marrow passing by at those levels, or actually included within the corresponding portions of it.

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Psyche and Soma The next steps were all precautionary measures. Thus, upon consideration of its supremely critical role, the marrow was wholly shielded inside a set of bony canisters that provide excellent protection for it because of their rigidity. Nevertheless, this very quality turns such containers fragile and poorly effective for guarding their precious contents against extreme weather and other external forces. On this account the bones were in turn wrapped in soft flesh, so as to cushion the delicate marrow inside against hard blows, as well as to isolate it from excessive heat or cold in the surroundings. Along the way, ligaments or sinews (neura) capable of contraction and extension were attached to the movable members, so that the body could flex itself and extend back again. Accordingly, bone and flesh were both conceived and installed entirely for the sake of carrying the marrow in as secure and stable conditions as possible. Two features should be noted in this system. The first is that no distinction is made between the substance that we still call “bone marrow” today, on one hand, and the nervous (p.19) tissue inside the cranium and the vertebral column, on the other; a similar soft content encased in bone is found in both instances. It makes sense, therefore, to conclude that they are but slightly different variants of the same pattern. Moreover, it seems straightforward to assume that there is continuity of the marrow throughout the body, so that it fills the head, then stretches down through the spinal canal immediately below, and finally extends out inside the bones along the limbs. The marrow is thus the immediate binding link of the tripartite soul to the whole body. A related important point to note here is that Plato’s Pythagorean anatomy is totally devoid of nerves and muscles in the senses given later to these words. Such organs would be distinguished until some 100 years after Plato’s death. As mentioned above, body movement is described in the Timaeus as carried out by contraction and extension of sinews (neura)—that is, one class of the four main components of the body according to Empedocles—which are “made out of a mixture of bone and unfermented flesh, to make up a single yellow stuff whose character was intermediate between them both.”49 Muscle function was thus conceptualized and ascribed to a specific type of structure, even though muscle tissue itself was regarded as merely cushioning and insulating “flesh.” General coordination of the whole is in charge of the tripartite soul, directly by means of the unified chain of command provided by the marrow inside the bones. No need is reported here for pale thin processes coming out from the skull and the spine (i.e., nerves) in

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Psyche and Soma order for the marrow to communicate with other bodily parts for the purposes of perception and motion.

Respiration, which according to the Timaeus50 is carried out by a complicated apparatus, is a process for the adequate management of air and fire in the body, but has little to do with the soul. Its main function is to assist nutrition, for fire follows air into the body, and once it gets to the belly it helps to dissolve food and drink, breaking them into tiny parts that are sent throughout the body in “the currents of the veins.” Thus Plato, using Timaeus as his mouthpiece, accounted for some of the physiological phenomena that we shall be dealing with in subsequent chapters of this book. As already mentioned, this particular Platonic dialogue was to exert enormous influence on the mental picture about the physical world for many centuries to come. It obviously also produced an impact in Plato’s own time, especially among students in the Academy, of course, although not always as the master professor would have perhaps expected and liked.

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Figure 1.8: Plato (left) and his brilliant pupil Aristotle (right) discuss their conflicting views as they come into a large hall to join a gathering of many outstanding intellectuals from antiquity; while Plato points to heaven in reference to focusing on the superior realm of ideas, Aristotle claims that the down-toearth world is also worth detailed investigation. (Center detail of The School of Athens, famous allegorical fresco painting at the Vatican by the great Renaissance artist Raffaello Sanzio; public domain picture, freely available by courtesy of the Web Gallery of Art at http://commons.wikimedia.org/wiki/ File:Sanzio_01_Plato_Aristotle.jpg.)

Psyche and Soma One of Plato’s favorite pupils, an independently minded Macedonian named Aristotle, would not buy for long into this dubious mix of Pythagorean medical theory and wild allegories. Instead he embarked on a methodical investigation of the universe, in the hope of identifying general principles in nature like those that had been sought after by his pre-Socratic forerunners. He reported his observations and insights in a number of treatises, most of them as lengthy as the Timaeus, with several of them devoted to the special problems posed by the understanding of living creatures. The differences between Plato, a philosopher in today’s sense of the word, and his talented student, destined to become the greatest naturalist of antiquity, are profound. These were quite clear in the Renaissance, so as to be cleverly dramatized by the great artist Raffaello Sanzio (1483–1520) in one of his major masterpieces, the School of Athens (Fig. 1.8). Here, an elderly Plato talks while aiming toward heaven, the supreme example of perfect order, while the younger Aristotle points down to earth, where things behave in more complicated ways. A brief review of Aristotle’s physiology will constitute the following section of the present chapter.

Aristotle’s Lyceum One explanation for the keen interest of Aristotle (384–322 BCE; Fig. 1.9) in the physical world is perhaps his having been born into a family with a long medical tradition from both parental lines. His father was the personal physician to Amyntas III, King of Macedonia (d. in 370 BCE), so the future philosopher must have had a privileged education in childhood, probably enriched with numerous observations about the functions of the human body. Later on Aristotle moved from Stagira, the town of his birth and infancy in (p.20)

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Psyche and Soma Macedonia, to Athens. Here he would stay for about 20 years in the Academy, evolving from being one of many young apprentices to become one of Plato’s possible successors as head of the institution. When, due to political reasons and to his foreign origin, he was bypassed in the selection and the post was assigned to one of Plato’s nephews, Aristotle realized he should be professionally independent in order to move ahead.

After a period of traveling around and studying at various places, he was called back to his homeland by the new King of Macedonia, Philip II (382– 336 BCE), with the request of taking charge of educating the 13-year-old prince Alexander III. Later on this youngster would demonstrate exceptional military abilities with which he would expand his political power, and with it Greek cultural influence, over the largest empire the world had ever known. Still, after only 3 years at the Macedonian court, Aristotle left for another relatively short stay at his birthplace, and eventually returned to Athens resolved to initiate his own school of philosophy there.

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Figure 1.9: Aristotle (384–322 BCE), the greatest naturalist philosopher in antiquity, conducted wide-ranging research on animal anatomy and physiology, among many other subjects, eventually offering a concept of the soul radically different from that imagined by his mentor Plato. (Marble portrait, Roman copy after a Greek bronze original by Lysippos from 330 BCE, now exhibited at the National Museum, Rome; public domain picture, freely available by courtesy of Jastrow at http:// commons.wikimedia.org/wiki/ File:Aristotle_Altemps_Inv8575.jpg.)

Psyche and Soma The new institution was established in a former teenager school—a gymnasium —just outside the city, in a suburb opposite to that where the Academy was located, and close to a temple in honor of Apollo Lyceus. Hence the place, which Socrates had been fond of visiting, became known as the Lyceum following its inauguration in 335 BCE. In contrast to Plato’s club of almost pure speculation among friends, Aristotle created something more like a research institute staffed by specialists working on diverse disciplines, with the help of assistants and collectors of animal, vegetable, and mineral specimens.51 Animal dissection was a regular practice, and the library gradually gathered the largest holdings in town on a variety of subjects. Teaching was mainly in the open, with faculty members ceaselessly walking with their students every morning and afternoon along the covered alleys that surrounded the Lyceum’s gardens—the famous peripatos from which the name “peripatetics” was since given to Aristotelian philosophers. The scientific orientation of the Lyceum, though not as wholly divergent from Platonism in its early stages as has sometimes been claimed, effectively rescued the naturalism of the pre-Socratic philosophers while also adopting the theoretical approaches of the Hippocratic physicians. The purpose was always to find out why things are as they are, and act as they do, even if the concluding answer was invariably that things are and act as it suits best their particular roles in a carefully ordered universe. The transcendent mission of any study was therefore to discover and understand this “teleological” relationship—that is, the ultimate finality or usefulness of each thing involved in the problem under consideration. This kind of research does make use of speculation, but unlike that in the Academy, the theories were largely based on systematic observation of objective facts, and formulated according to a rigorous rational procedure, a brand of logic invented by Aristotle himself.

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Psyche and Soma Notwithstanding the compulsory teaching-while-walking twice a day, the director of the Lyceum still found time to write a lot on a number of topics, from physics to rhetoric. Unfortunately the reliability and actual authorship of Aristotelian treatises is today uncertain.52 Many of these writings might have been provisional drafts prepared for a lecture, and Aristotle occasionally changed his mind on a particular subject, like any other thinker working on edge problems that often involve conflicting observations. Some of the works attributed to him might also have been authored by younger philosophers such as Theophrastus (c. 371–c. 287 BCE), Aristotle’s successor as the head of the Lyceum. Most probably there were also notes varying in quality taken by the students themselves. In addition, several titles that might have been important to make more sense out of the overall context in the Aristotelian corpus are now known to be lost. Adding to the complexity, after Aristotle’s death his writings were hidden for a long time, and when they surfaced again they were edited and packaged in ways that (p.21) make it hard to tell exactly what he might have written himself, what came from other writers in the Lyceum, and what was modified by later generations. It is no wonder, then, that large and small inconsistencies abound in an otherwise highly structured and vast intellectual construction destined to last in nearly unshaken condition for about 2,000 years. We shall now review what Aristotle and other faculty members at the Lyceum (i.e., the first Aristotelians or peripatetics) seemingly wrote on the basic biological questions that have led us into this inquiry. For convenience we shall follow the usual practice of referring to Aristotle as the author, drawing from several of his attributed treatises as needed for our present objective.53

A New Concept of “Soul” Aristotle did not share the fantasies described in the Timaeus, especially in everything that regards the soul. In fact, in an expressly dedicated treatise—On the Soul—that can be considered as the first book to have been written on general animal physiology, he rebuts all the previous hypotheses on the subject before expounding his own theory. To begin with, he says, it is false not only that the essence of the soul is to move by itself, but also that it might have the faculty of moving at all.54 On the contrary, the essence of the soul is its immutability, for on this property the identity of every living thing depends. The main distinction between a living thing and those belonging in the inorganic world is precisely its being composed of organs—that is, of interrelated instruments that collaborate in order to produce the organism’s life. In turn, each kind of organism is distinguished from all other kinds because its organs are arranged in a particular manner for a particular kind of life. This unique type of life, which only emerges from a peculiar organization of the body, is the specific soul of any living being. Here is an example: Page 27 of 47

Psyche and Soma Suppose that the eye were an animal —sight would have been its soul, for sight is the substance of the eye which corresponds to the account, the eye being merely the matter of seeing; when seeing is removed the eye is no longer an eye, except in name—no more than the eye of a statue or of a painted figure. We must now extend our consideration from the parts to the whole living body; for what the part is to the part, that the whole faculty of sense is to the whole sensitive body as such.55 Accordingly, Aristotle concluded, “we can dismiss as unnecessary the question whether the soul and the body are one; it is as though we were to ask whether the wax and its shape are one, or generally the matter of a thing and that of which it is the matter.”56 Since the soul is the functional organization of a living body, it is nonsense to think that the soul could be separated from its body, and more ridiculous still to believe that it—or part of it—might lodge successively in different bodies, as the Pythagoreans and Plato taught. For the same reasons, it is also wrong and simple-minded to imagine the soul as divided or distributed in only such-andsuch regions of the body, as is stated in the Timaeus. Aristotle preferred instead to think of the soul as having several faculties or powers, which obviously vary among different categories of living forms—that is, merely self-nutrient and generative in plants, plus also sentient and motive in animals, and in addition intelligent or rational in humans.57 He admits that there seems to be another widely different kind of soul that is responsible for the mind or power to think,58 but evidently was far more interested in understanding the other “psychic” faculties (i.e., those involved in the management of living bodies). Reasoning as a biologist, Aristotle translated Plato’s tripartite soul into general functional capacities and recognized that these are unequally distributed in the scale of all living beings.

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Psyche and Soma Now, every organization needs to have a directive center, and so does the soul, the seat of which resides in the heart in sanguineous animals or, in the invertebrates and other bloodless beasts, in an organ analogous to the heart. Here Aristotle sided with those who, like Empedocles, assigned a dominant role to the heart; and he turned against those who, like Alcmaeon and Plato, placed the soul or main part of the soul in the encephalon. His arguments for this decision are, among many others, the invariably central location of the heart, the warmth associated with it, its multiple connections with all other parts of the body through the vessels, and the fact that it is the first part that can be seen displaying motion in embryos. In stark contrast, he wrote, that the brain “has no continuity with the organs of sense is plain from simple inspection, and is still more clearly shown by the fact, that, when it is touched, no sensation is produced; in which respect it resembles the blood of animals and their excrement.”59 Understandably, few modern neuroscientists have forgiven Aristotle for such comments; and yet we go on printing Valentine cards decorated with hearts instead of brains, much as we continue to memorize “by heart.” Still, Aristotle assigned a highly critical role to this organ that fills the head. He conceived of it as a sort of radiator that helps to protect the whole body against overheating, by means of an efficient dissipation of the tremendous heat that is continuously generated in the heart.60 For: the soul is, as it were, set aglow with fire in this part, which in sanguineous animals is the heart and in the bloodless order the analogous member. Hence, of necessity, life must be simultaneous with the maintenance of heat, and what we call death is its destruction.61 It is actually this heat that ceaselessly emanates from the heart that distinguishes a living from a dead body, even when its specific form—or soul, according to Aristotle as mentioned above—continues to be apparently the same for some time after dying. The heat generated in the heart is so great indeed that, whereas in bloodless animals the (p.22) surrounding air or water passing by are usually enough to moderate their internal temperature, in the sanguineous ones lungs are further necessary too, apart from the cool brain, for continuous refrigeration.62 As we shall see next, such intense heat is also why the heart is the fountain of pneuma within the body, and therefore always contains the maximum amount of it.

The Main Instrument of the Soul

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Psyche and Soma Aristotle gives his clearest definition of pneuma in the treatise dedicated to animal reproduction. This process is initiated and carried out by the male semen, which constructs the embryo by acting like a carpenter or a potter, using the raw materials supplied by the female.63 Such goal-directed creative activity is possible because the semen contains “vital heat,” since it is “a compound of breath [pneuma] and water, and the former is hot air.”64 This latter concept, which coincides with that Diogenes had brought forth for soul, is further clarified when Aristotle goes on to state that the vital heat included in the semen is a “natural principle in the breath [pneuma], being analogous to the element of the stars”65 (i.e., the Aether). This last term also has, like “soul,” a long history. The Aether, traditionally situated by ancient Greeks at the hot uppermost level above the earth, was viewed by Aristotle as a fifth element or “quintessence” with special properties very different from those in the Empedoclean quartet. In Aristotelian chemistry, these four common elements are just aspects of a single substance that gets transformed under the effects of opposite qualities like the hot and the cold, the moist and the dry, and so on. Thus fire, for example, is the basic substance whenever the hot and the dry predominate, but it will become air if the dry is substituted by the moist. Similarly, water results from air by simply exchanging the hot with the cold, and will in turn convert to earth if the moist is replaced by the dry. Aether, in contrast, has a peculiar nature of its own. It is immutable and found exclusively in the outer region of the cosmos, above the moon, where the sun and the stars slide in regular and predictable order. Its most remarkable feature is a continuous circular motion, clearly distinct from the “natural” movements— which either are ascending or descending, and always finite—typical of the four elements common in the sublunary space. It is therefore especially significant that the pneuma in animals, which Aristotle called “connate pneuma” because it is present in them from the earliest embryonic stage, contains a principle related to this quintessence, since it thus combines the attributes of the hot and of continuous motion. This pneuma is originated by the intense heat in the heart through a process similar to “boiling,” which brings it out from that liquid stuff “of which the food furnishes a constant supply.”66 Actually the cardiac beating is due to the periodical expansions of this fluid being pneumatized—a term often translated as “volatilized”—as the heart turns it into blood through a sort of cooking under the effects of the same heat it generates. As part of such recently elaborated blood overflows into the vessels—we are left to conclude—the heart diminishes in size again. Accordingly, it is the expansion phase (or diastole) of the cardiac cycle that Aristotle takes as active, instead of the shrinking one (systole) as it was later determined.

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Psyche and Soma It is in the heart, too, “that we must look for the common sensorium belonging to all the sense organs.”67 The routes followed by vision, hearing, and smell from their respective sense organs to the heart, however, are seemingly not direct. For despite the aforementioned assertion that the brain “has no continuity with the organs of sense,” elsewhere Aristotle recognizes, like Alcmaeon before him, the presence of some links from the eyes and other senses with the brain and cerebellum, though of course such tracts ultimately reach the heart. In his words: The sense-organ of the eyes is set upon certain passages [pores], as are the other sense-organs. Whereas those of touch and taste are simply the body itself or some part of the body of animals, those of smell and hearing are passages connecting with the external air and full themselves of innate spiritus [connate pneuma]; these passages end at the small blood vessels about the brain which ran thither from the heart.68 At least the “pores” or passages related to smell and hearing are said to be full of connate pneuma. Since such passages connect with blood vessels it is likely that Aristotle, like Diogenes and the Hippocratic physicians before him, accepted the common view that the vessels contain pneuma as well as blood, both of which could provide continuity between the sense organs and the heart.69 Further, Aristotle had even more evidence in support of this continuity thanks to the superior anatomical techniques developed at the Lyceum. Apparently most previous researchers had inspected bodies after practicing the traditional procedure used by butchers to sacrifice livestock—that is, bleeding the animals to death so that the empty veins, devoid of an elastic wall like that of arteries, would collapse and thus become difficult to discern. Instead, Aristotle advised allowing “animals to starve to emaciation, then to strangle them on a sudden,”70 in order to render at least the superficial vessels clearly visible already in life. This method produced a far more complete description of the mammalian cardiovascular system, in which an uninterrupted connection of the heart with virtually every bodily part could be ascertained. Thus, presumably in Aristotle’s view, any change caused by external factors upon the sensory organs could be transmitted to the (p.23) heart through this continuous pathway of pneuma and blood. However, the extant Aristotelian texts say nothing about this.

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Psyche and Soma Even less information exists about how Aristotle explained the motor faculty of the soul—that is, how the heart manages to move the body in response to the impressions received through the senses. We should note at this point that neura or sinews, which Plato associated directly with body movements, could not be involved in the transmission of motor commands in Aristotelian physiology. The reason is that, though all of the neura were conceived as originating in the heart, they would not constitute an uninterrupted sequence like the vessels.71 It is therefore difficult to imagine how communication would proceed from the ruling center to the many moving parts in the periphery. The flesh (i.e., soft tissues including muscle) also could not participate much in this process, because according to Aristotle the flesh is the organ of touch.72 Although self-motion is of course the most evident of the psychic faculties, Aristotle scarcely dealt with it in the treatise On the Soul, probably because he regarded the subject as important enough as for writing two separate works about it. One of them (Movement of Animals) discusses the immediate cause of bodily movement, whereas the other (Progression of Animals) analyzes different types of locomotion. This detailed attention to the problem was fully justified: “For, if we except the movement of the universe, things with life are the causes of the movement of all else, that is of all that are not moved by one another by mutual impact.”73 According to Aristotle, the external movements of animals are always induced by something they want or they reject, either to satisfy an appetite or to avoid some pain. In each case the motivation springs from mind or desire, and both of these affect the heart. As the final recipient of all sensations, the heart reacts immediately to such stimuli with alterations in its own movement (e.g., an increased rate of beating or palpitations). Since the heart is also the source of pneuma, the characteristic of which is precisely the power of expanding and contracting, all the evidence points to this site as the origin of bodily motion. Pneuma appears to act in this view as an elastic linkage capable of thrusting and pulling in relation to this fixed point, the heart, center of the soul.74 Any irregularity in the normally symmetrical motion of the heart —we should probably understand— will elicit a twitch in the same direction and proportional in magnitude elsewhere in the body. No doubt the pulses sent from the heart by means of the connate pneuma will seem too weak and local as for activating a large and powerful body effectively. Yet Aristotle provides a few considerations that may help us to grasp his thinking better in this regard. First, the whole apparatus is built as to respond to very small changes, for the “movements of animals may be compared with those of automatic puppets, which are set going on the occasion of a tiny movement; the strings are released, and the pegs strike against one another.”75 In addition, the mechanical relationships among different parts are such that the effects become naturally amplified, Page 32 of 47

Psyche and Soma just as by shifting the rudder a hair’s breadth you get a wide deviation at the prow. And further, when by reason of heat or cold or some kindred affection a change is set up in the region of the heart, even in an imperceptibly small part of the heart, it produces a vast difference in the periphery of the body—blushing, let us say, or turning white, goose-skin and shivers and their opposites.76 Heat and cold, as mentioned in the above quotation, or more specifically a local change of temperature induced by sensations or imagination, is the immediate cause of motion in any body part. Upon exposure to such changes the body parts, says Aristotle, “change from solid to moist, and from moist to solid, from soft to hard and vice versa.”77 Some of these movements are involuntary, and not all of them depend on the heart: “By involuntary I mean motions of the heart and of the penis; for often upon an image arising and without express mandate of the intellect these parts are moved.”78 Finally, there is a class of organic movements, including respiration, sleep, and waking, which Aristotle calls non-voluntary because they do not arise from desire nor from imagination, though they nevertheless also result from natural changes in temperature.79 These changes of temperature in different locations of the animal body could well be explained as due to variations in the amount of pneuma—hot air (see above)—that they contain or receive from the heart at a given moment, but the Aristotelian texts offer no clue as to allow even a tentative suggestion in this regard. We do know that he considered “reasonable that nature should perform most of her operations using breath [pneuma] as an instrument, for as some instruments serve many uses in the arts, e.g., the hammer and anvil in the smith’s art, so does breath [pneuma] in things formed by nature.”80 On the other hand, however, there is virtually no information about how he thought this versatile tool might have actually worked. It is indeed paradoxical that Aristotle conferred so much importance to the connate pneuma, and yet was so poorly explicit on the subject, thus leaving ample ground for scholarly debate.81

After Aristotle Aristotle’s conception of pneuma as hot air, inherited from Diogenes and slightly modified, provided a model that was to impregnate Greek thought for a long time. Its imprint can be found in the two rival philosophical schools that dominated the scene for the following 500 years and beyond.82 (p.24) Galen (129–200), the great Pergamon-born Greek physician to several Roman emperors during the second century CE, and about whom we shall have much more to say in the following chapter, described those schools with the following words:

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Psyche and Soma Now, speaking generally, there have arisen the following two sects in medicine and philosophy among those who have made any definite pronouncement regarding Nature. I speak, of course, of such of them as know what they are talking about, and who realize the logical sequence of their hypotheses, and stand by them…The one class supposes that all substance which is subject to genesis and destruction is at once continuous and susceptible of alteration. The other school assumes substance to be unchangeable, unalterable, and subdivided into fine particles, which are separated from one another by empty spaces.83 The first-mentioned of those schools of philosophy was Stoicism, so named in reference to having been started at the stoa or public portico in Athens’ bustling downtown center. As with the pre-Socratic philosophers, only fragments and second-hand reports remain of the numerous works written by the Stoics. Nevertheless Galen himself, while debating the doctrines of one of their leading masters, the by then long-deceased Chrysippus of Soli (c. 279–c. 206 BCE; Fig. 1.10), has transmitted to us how they conceived the soul as constituted of pneuma consisting of some mixture of air and fire: Whereas the soul’s parts, as you yourself explain fully elsewhere, are the auditory pneuma, the optic (pneuma), and in addition the vocal and the generative (pneumas), and over all of them the governing (pneuma) in which, you said, reason is constituted; and…Now this pneuma has two parts, elements, or states, that are intermingled throughout, the cold and the hot, or, if you wish to use different appellations and give them the names of their substances, air and fire, and it also takes some moisture from the bodies in which it dwells.84 As Galen also informs us here, the Stoics imagined this pneumatic soul as composed of seven parts, six of them being branches that would stem from a reasoning and governing center, the hegemonikon located in the chest; from here all other six subordinate parts of the soul “grow out and stretch out into the body like the tentacles of an octopus,” reports another ancient source.85 Hence, the Stoics also preferred the thorax, if not exactly the heart like Empedocles and Aristotle, as the main seat of the soul rather than the head, which Alcmaeon and Plato favored. Nevertheless, at least in the period following Aristotle, Stoic physiology seems to have gone through some theoretical turbulence, if we are to believe the Roman writer Lucius Seneca (c. 54 BCE–c. 39 CE), who commented about a controversy that Chrysippus had with his own teacher: Cleanthes and his pupil Chrysippus did not agree on what walking is. Cleanthes said it was breath [spiritus],

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Psyche and Soma extending from the commanding-faculty to the feet, Chrysippus that it was the commanding-faculty itself.86

As we shall see next, this particular problem seems not to have existed among the adherents of the second philosophical sect mentioned by Galen, which became known as Epicureanism after the name of its founder, Epicurus (see below). In fact this school derived straight from a quite independent line of pre-Socratic reasoning— atomism—in which, instead of only four, a large number of substances were believed to compose the world. All of them, whether homogeneous or heterogeneous, were viewed as aggregates of individually invariable and indivisible particles (a-toma) of different sizes and shapes. In his review of previous ideas about the soul, Aristotle relates that according to Democritus (c. 460–c. 370 BCE; Fig. 1.11), the best-known representative of that philosophical position, (p.25)

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Figure 1.10: Chryssipus of Soli (c. 279–c. 206 BCE), the third successive head of the Stoic school of philosophy in Athens. Nearly 400 years later, Galen attacked the Stoic philosopher’s conception of the soul as a pneumatic system consisting of several appendages linked to a central commanding center (hegemonikon) located within the chest. (Marble portrait by an unknown Roman artist, copied after a lost Hellenistic original from the late third century BCE, exhibited at the British Museum, London; public domain picture, freely available by courtesy of Marie-Lan Nguyen at http:// commons.wikimedia.org/wiki/ File:Chrysippos_BM_1846.jpg.)

Psyche and Soma soul is a sort of fire or hot substance; his ‘forms’ or atoms are infinite in number; those which are spherical he calls fire and soul, and compares them to the motes in the air which we see in shafts of light coming through windows…the spherical atoms are identified with soul because atoms of that shape are most adapted to permeate everywhere, and to set all the others moving by being themselves in movement.87 Then, two pages later, Aristotle ridicules Democritus: Some go so far as to hold that the movements which the soul imparts to the body in which it is are the same in kind as those with which it itself is moved. An example of this is Democritus, who uses language like that of the comic dramatist Philippus, who accounts for the movements that Daedalus imparted to his wooden Aphrodite by

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Figure 1.11: Democritus (ca. 460–ca. 370 BCE), along with the slightly older Leucippus, first devised the theory of atomism. Instead of the classic four elements, they conceived the world as composed of a huge number of different substances, all consisting of diminutive indivisible particles (a-toma) with peculiar shapes that allowed them to associate forming different aggregates, and all forever moving in a boundless vacuum. It is this theory that some 100 years later was adopted and further developed by Epicurus (Fig. 1.12). Democritus is sometimes referred to and represented as, like in this picture, a “laughing philosopher” because of his optimistic stand, notwithstanding his materialistic philosophy. (Detail of line engraving by L. Vorsterman after an original imaginary portrait by P. Rubens; Wellcome Library, cat. V0001526.)

Psyche and Soma saying that he poured quicksilver into it; similarly Democritus says that the spherical atoms owing to their own ceaseless movements draw the whole body after them and so produce its movements.88

Nevertheless, in the immediate post-Aristotelian generation of philosophers, when Epicurus (341–270 BCE; Fig. 1.12) took up atomism and projected his own brand of this theory into the Hellenistic world, the atomistic soul was already a mixture of fire or heat with air (plus another innominate ingredient):

Figure 1.12: Epicurus (341–270 BCE), a major advocate of the atomistic philosophy in the early Hellenistic period, won numerous followers in the Roman Empire as the thinker at the hub of one of the two main rival philosophical schools still discussed 400 years later by Galen (author reviewed in Chapters 2 and 11). Epicurus’ ethics, derived from his materialistic outlook, recommended enjoying life while it lasts, pursuing simple pleasures and avoiding pain or distress if possible. (Marble portrait, a Roman copy from the first century CE after a Greek original from the third century BCE, now exhibited at the National Museum, Rome; public domain picture, freely available by courtesy of Marie-Lan Nguyen at http:// commons.wikimedia.org/wiki/ File:Epicurus_Massimo_Inv197306.jpg.)

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Psyche and Soma The next thing to see—referring it to the sensations and feelings…—is that the soul is a fine structured body diffused through the whole aggregate, most strongly resembling wind with a certain blending of heat, and resembling wind in some respects but heat in others. (p.26) But there is that part which differs greatly also from wind and heat themselves in its fineness of structure, a fact which makes it the more liable to co-affection with the rest of the aggregate. All this is shown by the soul’s powers, feelings, mobilities and thought processes, and by those features of it whose loss marks our death.89 A couple of centuries later, Greek Epicureanism was introduced into the rising Roman Empire by the poet-philosopher Titus Lucretius Carus (c. 99–c. 55 BCE), better known today simply as Lucretius, who presents that same constitution of psyche, yet now in its Latin translation as anima: Just as in the flesh of any living creature there is a scent and a certain heat and flavour, and yet from all these is made one body grown complete: so heat and air and the unseen power of wind commingled form one nature along with that quickly moving force, which from itself distributes amongst them the beginning of motion, whence first the sense-bringing motion arises spreading through the flesh. For this nature lies deep down, hidden in the most secret recess, and there is nothing in our body more deeply seated than this; and it is itself furthermore the spirit of the whole spirit [anima est animae].90 Soul was then for Lucretius, just as it was for Epicurus, a thorough blend of heat, air and wind, the composite being in turn commingled with a “quickly moving force” that acts like a “soul of the soul.” The Latin name given by Lucretius to this enigmatic force is animus, and he explains how it interacts with the anima in order for us to walk: When the mind [animus] so bestirs itself that it wishes to go and to step forwards, at once it strikes all the mass of spirit [anima] that is distributed abroad through limbs and frame in all the body. And this is easy to do, since the spirit is held in close combination with it. The spirit [anima] in its turn strikes the body, and so the whole mass is gradually pushed on and moves.91 Since Lucretius admired Epicurus intensely and stayed close to the doctrines of his Greek predecessor, there is no hint of any theoretical disagreements between pupil and teacher about how walking takes place, such as that between Chrysippus and Cleanthes among the Stoics (see above), or between Aristotle and Plato about a number of issues.

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Psyche and Soma We should recognize, however, that Lucretius is included in this chapter only for the direct relation of his work with that of Epicurus. When bringing up the Roman poet’s presence here, we must note that this chapter has reached too far ahead and gone into a completely different world, when Greece was no longer the dominant power in the West. After giving birth to Stoicism and Epicureanism, the cultural splendor and allure of Athens began to decline. Concomitantly, another Greek intellectual center across the Mediterranean in Alexandria, Egypt, flourished during the Hellenistic period immediately following Alexander’s conquests. A number of important developments—military, political, and scientific—occurred in the meantime, and they will be among the subjects that will occupy us in the following chapter. Before closing, however, let us briefly summarize where this first stage of our “spirit” searching journey has taken us.

Concluding Remarks In this chapter we have tried to survey the major initial ideas developed in ancient Greece to account for animation of living bodies in terms of almost purely natural mechanisms. The evolution was a complex one, for although all parties agreed that the presence of soul in the body marks the difference between life and death, few agreed on what soul actually is. Views varied from conceptualizing the soul as (1) a share of the fundamental element of choice in apparently pure form (air for Anaximenes, fire for Heraclitus), to (2) a combination of elements or qualities (warm air for Diogenes, a certain blend of air and heat/fire for the Stoics and the Epicureans), to (3) a multi-part entity made up of a special mixture of inferior-grade residues of “Being,” “Same” and “Different” (according to Plato), to which we should add (4) the naturally unchanging specific form of a living being that intrinsically endows its body with the particular set of psychic faculties required for that organism’s life (in Aristotle’s revolutionary view). Neither could the basic organization of the plainly visible and tangible body attain the benefit of a general agreement at this time. The philosophical schools were divided, especially as regards the location of the ruling center where the soul, or at least the main part of it, would reside. While Alcmaeon, the Pythagoreans, and Plato identified the head as the seat of that soul, Empedocles, Aristotle, and the Stoics argued in favor of the heart, or the thorax, for this key position. Many other fundamental matters were equally controversial. Thus Plato and Aristotle were at odds, for example, as to whether the flesh around bones is just a protective and insulating wrapping material (Plato) or the organ of touch (Aristotle).

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Psyche and Soma Nevertheless, a common motif can be distinguished in between some of the aforementioned discordant voices. This point of relative convergence is that all life depends on, or is closely associated with, a self-moving though invisible fluid, be it magnetism (Thales), air in motion—either wind or breath (Anaximenes), a warm exhalation (Heraclitus), or warm air (Diogenes, Aristotle, Stoics, Epicureans) that may derive its heat content from something analogous to Aether (Aristotle), the fifth element circulating perpetually at the highest levels of the cosmos. Pneuma, the Greek name commonly used for this fluid, is “the breath of life” that just like the early philosophers we are striving to envision and understand, as we try to imagine ourselves in different times and cultures through this book. Even the Pythagoreans admitted that a pneuma of some kind is intimately related to all life, hence their prohibition against eating beans. It is apparently only Plato, among the significant authors mentioned here, who viewed (p.27) pneuma merely as wind, or as the air current that goes in and out of animals during inhalation and exhalation, because his notion of soul needed it to be immaterial and thus wholly independent of matter. In view of the common motif that surfaces in the above survey, it is worth recalling some other salient properties of pneuma, apart from invisibility and self-movement. That it has holding power was allegedly stated early on by Anaximenes, and possibly meant before him by Thales too, in the likelihood that the soul to which the latter attributed magnetism might have been a pneuma-like soul. Though extremely tenuous, pneuma is substantially air and hence a body that occupies volume in space, as shown experimentally by Empedocles and Anaxagoras, a feature that may help us to understand its supposed interactions with other bodies. Thus, for example, pneuma within the animal body mediates the inward transmission of impressions received by the delicate sensory organs, such information being conveyed either through certain passages (poroi) or possibly via the blood vessels, as intimated by Alcmaeon and Aristotle. At a grosser level, according to Aristotle, contractions and expansions of pneuma also permit the transmission of motor commands from the heart to other body parts. Lucretius’ anima, almost indistinguishable from pneuma, also pushes the body in order to move it. And, in a more refined design, the Stoics believed that pneuma is branched and acts through specific pathways.92

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Psyche and Soma In summary, if not the soul (psyche or anima) itself, pneuma is at least its most versatile instrument in the opinion of a majority of ancient thinkers down to Aristotle, the Stoics, and the Epicureans. Diogenes and some of the Hippocratic physicians were even convinced that air (or pneuma) is intelligent in its own right, or at least a carrier of intelligence; consequently, it is responsible for keeping everything working properly both within and outside living bodies, as well as in the universe at large. It is hardly surprising therefore that, as we shall see in the following chapters, the concept of pneuma would continue to evolve, both in ancient physiology and in religion. At the close of the fourth century BCE, however, the theory of pneuma as a scientific concept was still in a process of gestation. As mentioned at the beginning of this chapter, many documents from antiquity are irretrievably lost, making attributions difficult. Yet it can be argued that for all we know it was the Aristotelian peripatetics, with their studies of living nature, who contributed the most to positioning pneuma in physiology as the main instrument of the soul. But even they, however, did not solve the problems associated with the various modes of pneumatic operation, and their cardiocentric theories were questioned and even challenged. The next stage in this development would require extended theoretical considerations as well as great anatomical discoveries.92 Notes:

(1) For a general introductory background about the period covered in this chapter see Lloyd, 1970; Bremmer, 1993; Nutton, 2004. A more compact review can be found in Crivelatto and Ribatti, 2007. (2) See discussion in the Prologue. (3) General overviews by subjects of pre-Socratic philosophy can be obtained in Barnes, 1979, and Long, 1999. For collected texts and studies of individual authors see Kirk and Raven, 1971. (4) Aristotle, On the Soul, I, 2, 405a20–21; DK 11 A 22 (ed. Barnes, 1995, vol. 1, pp. 645–646). All references to treatises by Aristotle are here addressed to, or quoted from, this edition of the revised Oxford translations. The standard notation for reference to works written by (or attributed to) Aristotle and other classic authors includes book, chapter, page, and sometimes line numbers. In this case the reference includes also a “DK” number—that is, the location given in a comprehensive catalogue compiled and revised respectively by Hermann Diels and Walther Kranz, where the views of Greek philosophers who lived up to Socrates’ time are collected from disperse data found in many ancient texts. (5) Ibid., I, 5, 411a8–9; DK 11 A 2 (ibid., p. 655).

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Psyche and Soma (6) Aetius, Placita, I, 3, 4; DK 13 B 2 (trans. Freeman, 1996, p. 19). The word pneuma is usually translated into English as “breath” or “spirit,” but it will help us here if we recall the original term in its technical sense of air in motion or wind. The above secondary source by Freeman, from which this and other quotations are here taken, is a complete English translation of supposedly original expressions of all the pre-Socratic philosophers, as compiled originally in German by Diels and Kranz (see note 4 above). Words in brackets within quotes added here. (7) Diogenes Laertius, Lives…, IX,19; DK 21 A 1 (trans. Hicks, 1995, vol. 2, pp. 426–427). (8) See for example Homer, Iliad, XX, 439 (trans. Murray, 1925, vol. 2, pp. 402– 403); Odyssey, VI, 20 (trans. Murray, 1919, vol. I, pp. 206–207). (9) Aristotle, On the Soul, I, 2, 405a25–26; DK 22 A 15 (ed. Barnes, 1995, vol. 1, p. 646). (10) Clement of Alexandria, Stromateis, VI, 17, Chapter 2; DK 22 B 36 (trans. Freeman, 1996, p. 27). (11) Ioannes Stobaeus, Eclogae physicae III, 5, 8; DK 22 B 118 (ibid., p. 33). (12) Diogenes Laertius, Lives…, IX, 3–4; DK 22 A 1 (trans. Hicks, 1995, vol. 2, pp. 410–413). (13) Ibid., VIII, 24–25 (ibid., pp. 340–343). (14) Aristotle, On the Soul, I, 2, 404a17–20 (ed. Barnes, 1995, vol. 1, p. 644). (15) Diogenes Laertius, Lives…, VIII, 24; DK 22 A 1 (trans. Hicks, 1995, vol. 2, pp. 340–341). (16) Plato, Timaeus, 42b-d, 90e-92c (trans. Zeyl, ed. Cooper and Hutchinson, 1997, pp. 1245, 1289–1291). All references and quotations to Plato’s works are here taken from this edition. (17) See discussion of the related notion of resurrection in Chapter 3. (18) Aristotle, Physics, VI, 9, 239b14–29; DK 29 A 26 (ed. Barnes, 1995, vol. 1, pp. 404–405). (19) Diogenes Laertius, Lives…, IX, 72; DK 29 B 4 (trans. Hicks, 1995, vol. 2, pp. 484–485). (20) Ibid., VI, 39 (ibid., pp. 40–41).

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Psyche and Soma (21) Aristotle, On the Soul, I, 2, 405a29-b1; DK 24 A 12 (ed. Barnes, 1995, vol. 1, p. 646). (22) For discussions in this regard see Lloyd, 1975; Doty, 2007. (23) Theophrastus, The Senses, 26; DK 24 A 5 (Stratton, 1917, pp. 88–89). (24) See references in note 22, especially Lloyd, 1975, for a thorough review of this subject. (25) Aetius, Placita, V, 24, 1; DK 24 A 18; see Lloyd, 1975. (26) Aristotle, On the Soul, I, 2, 404b11–15; DK 31 B 109 (ed. Barnes, 1995, vol. 1, pp. 644–645). (27) Simplicius, Physics, 300, 21 and 32, 3; DK 31 B 96 and 98 (trans. Freeman, 1996, p. 62). See also Solmsen, 1950. (28) Porphyry, On the Styx, I, 49, 53; DK 31 B 105 (trans. Freeman, 1996, p. 63). (29) Aristotle, On Youth, Old Age, Life and Death, and Respiration, 473b9–474a6; DK 31 B 100 (ed. Barnes, 1995, vol. 1, pp. 753–754). The Empedoclean simile of the clepsydra as an illustration of the process of breathing is universally considered as a landmark in the history of empirical science. However, its correct interpretation has been a field for serious and recurrent anatomicophysical controversies among historians (see Furley, 1957; Booth, 1960; O’Brien, 1970). The reader is therefore referred to these contrasting positions in order to extract a personal opinion on this matter. (30) Aristotle, Problems, XVI, 8, 914b9–16; DK 59 A 69 (ed. Barnes, 1995, vol. 2, p. 1423). (31) Aristotle, Physics, IV, 6, 213a23–27; DK 59 A 68 (ibid., vol. 1, pp. 362–363). (32) It is readily apparent to anyone that neither magnetic force, nor heat or air, can “permeate” with the same easiness through all materials. Yet the former two, in contrast to air, seem not to occupy a volume within the containing bodies. (33) Simplicius, Physics, 152, 22–153; DK 64 B 5 (trans. Freeman, 1996, p. 88). (34) Aristotle, History of Animals, III, 2, 511b30–512b10; DK 64 B 6 (ed. Barnes, 1995, vol. 1, pp. 813–814). (35) For a thorough study about Hippocrates and his followers see Jouanna, 1999.

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Psyche and Soma (36) “Hippocrates,” Breaths, 3 (trans. Jones, 2006, pp. 228–231). The author’s name is within quotation marks in the notes because the authorship is only conventionally attributed to the historical Hippocrates. The 70-plus medical treatises collectively known as the Corpus Hippocraticum, far from containing a coherent and consistent doctrine, reveal many fundamental disagreements. It is therefore now accepted by all scholars of the period that the collection includes the work of numerous authors who were active at different times over several decades. Hippocrates himself may have written only a few of the titles. The heterogeneity of this first medical library, however, provides an invaluable sample of the spectrum of views in those early stages of rational medicine in ancient Greece. (37) Ibid., 4 (ibid., pp. 232–233). (38) “Hippocrates,” Sacred Disease, 19 (ibid., pp. 178–179). (39) Ibid., 10 (ibid., pp. 160–161). (40) Hippocrates, Breaths, 14 (ibid., pp. 250–251). (41) Ibid., 13 (ibid., pp. 246–249). (42) Plato, Phaedo, 97d-98d (trans. Gruber, ed. Cooper and Hutchinson, 1997, pp. 84–85). (43) Plato, Timaeus, 30b-c (trans. Zeyl, ibid., p. 1236). (44) Ibid., 35a-36d (ibid., pp. 1239–1240). (45) Ibid., 41d-42a (ibid., p. 1245). (46) Ibid., 44d-47d (ibid., pp. 1247–1250). For a more detailed discussion of Plato’s model of the three-part soul, in relation to later schemes by Aristotle and Erasistratus (who will be reviewed in Chapter 2), see Smith, 2010. (47) Ibid., 69c-71d (ibid., pp. 1271–1272). (48) Ibid., 73b-74e (ibid., pp. 1274–1275). (49) Ibid., 74d (ibid., p. 1275). (50) Ibid., 78a-79e (ibid., pp. 1278–1279).

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Psyche and Soma (51) A further difference between the two leading philosophical centers in Athens, prosaic but determinant and seldom questioned, must have been operation costs. Faced with the prospect of financing substantial wages and many acquisitions, Aristotle probably obtained one or more grants. It has been a matter of long debate just how much help he may have received for this purpose from his former pupil Alexander, who by then was already the owner of half the world and ready to conquer the remaining half. For a review of this discussion see Romm, 1989. (52) The problem of authorship of Aristotelian works has been a matter of repeated debate; see for example Grayeff, 1956; Egerton, 2001. (53) For an overview of Aristotelian biology see Lennox, 2001. (54) Aristotle, On the Soul, I, 3, 405b32–406a2 (ed. Barnes, 1995, vol. 1, p. 647). (55) Ibid., II, 1, 412b18–24 (ibid., p. 657). (56) Ibid., II, 1, 412b5–9 (ibid.). (57) Ibid., II, 2–3 (ibid., pp. 657–660). (58) Ibid., II, 2, 413b25–26 (ibid., pp. 658–659). (59) Aristotle, Parts of Animals, II, 7, 652b4–7 (ibid., p. 1016). (60) Ibid., II, 7, 652b20–23 (ibid.). (61) Aristotle, On Youth, Old Age, Life and Death, and Respiration, 4, 469b16–20 (ibid., p. 748). (62) Ibid., 16, 476a15–476b15 (ibid., p. 756). (63) Aristotle, Generation of Animals, I, 22 (ibid., pp. 1134–1135). (64) Ibid., II, 2, 736a1–2 (ibid., p. 1142). (65) Ibid., 736b30–36 (ibid., p. 1143). For reviews about the relationships between pneuma, vital heat, and Aether, see Solmsen, 1957; Freudenthal, 1999; Lloyd, 2007. (66) Aristotle, On Youth, Old Age, Life and Death, and Respiration, 20, 479b30– 480a15 (ed. Barnes, 1995, vol. 1, pp. 761–762). (67) Ibid., 3, 469a10–13 (ibid., p. 747). The “common sensorium” or center of destination of all sensations is a notion that we will find again many times, usually with this same name, up to the 18th century.

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Psyche and Soma (68) Aristotle, Generation of Animals, II, 6, 743b35–744a5 (ibid., p. 1154); see also History of Animals, I, 16, 495a12–18 (ibid., p. 788). (69) See Peck, 1942, p. 593. (70) Aristotle, History of Animals, III, 3–4, 513a13–14 (ed. Barnes, 1995, vol. 1, pp. 814–818); for the complete procedural discussion see 513a9–515a26. (71) Aristotle, History of Animals, III, 5, 515a28–33 (ibid., p. 818). It is also worth noting here that Aristotle still used the word neura in its original sense; that is, to denominate tendons, ligaments, and aponeuroses as well as actual nerves in the later restricted meaning of the term. (72) Aristotle, Parts of Animals, II, 8, 653b19–30 (ibid., p. 1018). (73) Aristotle, Movement of Animals, 6, 700b11–13 (ibid., p. 1091). (74) Ibid., 10, 703a4–28 (ibid., pp. 1094–1095). (75) Ibid., 7, 701b2–4 (ibid., p. 1092). (76) Ibid., 701b26–32 (ibid.) (77) Ibid., 8, 702a1–10 (ibid., p. 1093). (78) Ibid., 11, 703b6–8 (ibid., p. 1095). (79) Ibid., 11, 703b8–17 (ibid.) (80) Aristotle, Generation of Animals, V, 8, 789b8–11 (ibid., p. 1218). (81) See for example Peck, 1942; Solmsen, 1957; Solmsen, 1961; Nussbaum, 1978; Freudenthal, 1999; Berryman, 2002. (82) For overviews of scientific development during the Hellenistic period see Lloyd, 1973, and Long, 1986. (83) Galen, On the Natural Faculties, XII, p. 27 (trans. Brock, 1952, pp. 42–45). (84) Galen, On the Doctrines of Hippocrates and Plato V, 3, 7–8 (trans. De Lacy, 2005, part I, pp. 306–307). Words in parentheses as in the source, introduced by the translator for an easier understanding of the text. (85) Aetius, Placita, IV, 21, 1–4 (trans. Long and Sedley, 1987, vol. 1, p. 315). (86) Seneca, Letters, 113, 23 (ibid., 316). Please note that the word spiritus used here, with which we shall be concerned throughout the remainder of this book, is the Latin translation from the Greek term pneuma.

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Psyche and Soma (87) Aristotle, On the Soul, I, 2, 403b32–404a8 (ed. Barnes, 1995, vol. 1, p. 644). (88) Ibid., 3, 406b16–22 (ibid., p. 648). (89) Epicurus, Letter to Herodotus, 63 (trans. Long and Sedley, 1987, vol. 1, p. 65). Like so many other Greek works, the numerous treatises reportedly written by Epicurus are lost, so that only isolated fragments, of which the present quote is an example, remain. Fortunately, however, in this case much of Epicurus’ philosophical doctrine has been reconstructed thanks to its ordered exposition in the book of his Roman follower Lucretius (see below). (90) Lucretius, On the Nature of Things, III, 266–277 (trans. Rouse/Smith, 1992, pp. 208–209). (91) Ibid., IV, 886–891 (ibid., pp. 346–347). (92) One last word is in order before continuing farther. Our follow-up of the main ideas developed in the ancient Greek world to account for animation of living bodies is admittedly far from complete. No mention has been made, for example, of the numerous and varied hypotheses competing for credence in explaining nutrition and assimilation, or perception by the different senses. Covering such fields and many others, including analogous or alternative ideas in Eastern cultures, would call for a much broader treatment than the one we have decided upon for this introductory story. For more background and references, the reader is referred to some existing treatises on the history of general physiology, including Hall, 1969; Rothschuh, 1973; Beare, 1906 (still good).

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Alexandria and Hellenistic Psychophysiology

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Alexandria and Hellenistic Psychophysiology C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0002

Abstract and Keywords This chapter takes a look at the evolution of the idea of internal pneumata, specifically the pneuma zootikon and the pneuma psychikon. It notes that there was a “silent period” during the history of animal spirit and discusses Claudius Galen, whose take on animal spirit persisted into the medieval period and beyond. This chapter shows that after the death of Aristotle until the death of Galenin, neuropsychological thought slowly evolved from a loose speculation to a more precise and anatomically grounded science. Furthermore, Galen's work was also revealed to be limited by the technical resources of his times, and the major outlines of his synthesis served as the background of biomedical understanding for the next millennium. Keywords:   internal pneumata, pneuma zootikon, pneuma psychikon, animal spirit, Claudius Galen, Galenin, neuropsychological thought, biomedical understanding

[T]his part which must be such as to control and govern the passage of the pneuma…is not the pineal body but the epiphysis that is very like a worm and is extended along the whole canal. Galen, de Usu Partium (On the Usefulness of the Parts of the Body) 1, 491 As the heart relaxes and contracts to accommodate and eject its material so the brain, when it needs to distribute pneuma psychikon contained in its ventricles to some parts of the body, sets the pneuma in motion. Page 1 of 20

Alexandria and Hellenistic Psychophysiology Galen: De placitis Hippocratis et Platonis, Book III, Chapter 8 We noted in the previous chapter that the 37-year-old Aristotle, the “intellect of the school” according to his master, Plato, was nevertheless passed over for the post of Director when Plato died in 348 BCE. This seems to have been largely due to the politics of the time. Aristotle was a Macedonian. Indeed, his father was physician to Amyntas, King of Macedonia. Antagonism between Athens and Macedonia was running high in the middle of the fourth century BCE. Amyntas’ youngest son, Philip, who had inherited the throne, was a particularly ferocious empire-builder. Famously he advised the Spartans to “submit without delay” for, he said “if I bring my army into your land, I will destroy your farms, slay your people and raze your city.” To which the Spartans replied with a laconic “If.” In this case Philip appears to have backed off, but the exchange illustrates Philip’s reputation. When Aristotle left Athens in 348 he spent a few years studying marine biology at Mytilene on the island of Lesbos and then returned to Macedon to spend a number of years at the court tutoring Philip’s son Alexander, who was later to become known as “the Great.” In 336 BCE Philip was assassinated and Alexander assumed the throne. In the same year Aristotle returned to Athens to found the Lyceum. The rivalry between Athens and Macedonia remained fraught and dangerous. In 322 BCE anti-Macedonian feeling once again ran high. Aristotle, the Macedonian, with his powerful Macedonian connections and background, felt it was time to move out once more. Thinking of the fate of Socrates, he is reputed to have said that he would not give Athenians a second chance to sin against philosophy. He sailed to the island of Calchis, where he died a few months later. Aristotle’s star pupil, Alexander (Alexander the Great), exhausted from his conquests and travels, had died a year earlier in 323 BCE. These two deaths are conventionally regarded as marking the end of the great period of Athenian philosophy and the beginning of the Hellenistic age. In contrast to the wideranging philosophies attempted at Athens, the thinkers of the Hellenistic age were, on the whole, specialists, more interested in detail than in over-arching schemata. In this, many have thought, they resemble our present age. In this chapter we start by following the development of the idea of internal pneumata —the pneuma zootikon and the pneuma psychikon—as it was elaborated in the great medical school at Alexandria. We shall then jump a “silent period” in the history of animal spirit until the times of Claudius Galen in the second century CE. Galen, as we shall see, in effect took up where Erasistratus left off nearly 500 years earlier. His take on animal spirit persisted into medieval times and beyond, as the following chapters will make clear.

A Research Institute at Alexandria

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Alexandria and Hellenistic Psychophysiology One of Alexander the Great’s most lasting achievements was the foundation of a city to bear his name—Alexandria. Plutarch describes the foundation thus: Alexander was visited by a dream while asleep near the Nile delta in which he seemed to be visited by the shade of Homer. Homer sketched out a town plan to include the island then named Pharos, on which the famous lighthouse was later built. Alexander immediately arose and outlined the plan in barley-meal (no chalk was available, it seems). Not surprisingly a huge flock of birds appeared in the morning and removed the outline. This was at first taken as an ill omen, but Alexander was later persuaded that all was well and the building went ahead. The year was 334 BCE and Alexander had 11 more years of conquest ahead of him. Alexandria grew and thrived. In the third century BCE the Ptolemaic rulers of Egypt (perhaps Ptolemy 1 or his son (p.30) Ptolemy 2) established a research center to rival Athens. This center consisted of two major, interlinked, units—the Museum and the Library (Fig. 2.1).

It was in these research centers that many of the great names of Hellenistic times worked and wrote their treatises. It was here that Euclid is said to have organized the book that some still regard as the supreme achievement of the human mind. Here Aristarchus first proposed a heliocentric astronomy and Ptolemy, later, designed the terracentric system consisting of cycles and epicycles that was adopted by all subsequent astronomers until in the mid-16th century

Figure 2.1: The Royal Library at Alexandria. (From Wikimedia Commons, ‹http://Wikipedia.org/ Image:Ancientlibraryalex.jpg›)

Copernicus showed that Aristarchus was, after all, right. Eratosthenes (275–194 BCE), the third librarian, worked out a surprisingly accurate figure for the circumference of the Earth. Technology and engineering were developed by Hero and Ctesibius. The 37-gear antikythera mechanism (although probably made in Rhodes) shows the level of sophistication reached by the second century BCE (Fig. 2.2).1 Some, indeed, think that the scientific method was discovered in these early centuries only to be lost during Roman times and rediscovered in the Renaissance.2

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Alexandria and Hellenistic Psychophysiology The biological sciences, especially anatomy and physiology, were also well represented. Herophilus, according to Galen, was the first man to have had the privilege of making a systematic dissection of the human body, and Erasistratus, his younger contemporary, worked out a neurophysiology that lay at the root of thought in this area until the 17th century of our era.

Alexandrian Neurophysiology We noted in Chapter 1 that Aristotle, greatest of biologists, never recognized the significance of the nervous system, indeed confusing nerves with sinews. His physiological system was profoundly cardiocentric. His dissection techniques were, however, taken up by his successors to develop an anatomically informed Figure 2.2: Principal fragment of the neurophysiology. We have, of antikythera mechanism. (From Wikimedia course, to be careful when Commons. ‹en.wikipedia.oorg/wiki/ discussing these early Fle:NAMA_d%27Anticythère_1.jpg›) physiologists. Few of their writings have escaped the ravages of time. The great library at Alexandria was destroyed, perhaps by Julius Caesar in 48 BCE, perhaps later; in any case, the great collections housed there disappeared, as did those of other significant libraries in the ancient world. So what we have of these ancient physiologists is at best second hand and often far worse. The temporal relationships of the great biomedical figures of the Hellenistic age are shown in Figure 2.3.

Praxagoras of Kos (b. 340 BCE) Tradition tells us that Praxagoras of Kos, a younger contemporary of Aristotle, used the dissection techniques developed in the Lyceum to distinguish clearly between arteries and veins.3 He is also credited with being the first to show (p. 31)

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Alexandria and Hellenistic Psychophysiology that a pulse can be detected in the arteries. He recognized this as an important sign of life. The tradition also records that he observed the arteries to continue to pulsate when removed from animals during vivisection. Was he thinking of the heart? Or is there a mistranslation? Finally, and significantly for our history, he is said to have gone a step beyond Aristotle to argue that while the veins contained blood, the arteries contained pneuma.

This belief must seem strange to modern minds. Surely, it will be said, cutting an artery, which must have been a common occurrence and not only on the vivisection bench, would have resulted in a spurt of arterial blood in antiquity as it does now? So does it not follow that the arteries contain blood in the living body, not pneuma? There seem to be at least three reasons for Praxagoras’ seemingly counterfactual belief. The first was metaphysical. This should not be dismissed out of hand. Thought-worlds, as we noted in Chapter 1, demand coherence. Great efforts are made to accommodate seemingly contrary

Figure 2.3: Timeline showing the temporal relationships of the significant figures in this chapter. Al = Alexander the Great; Ar = Aristotle; Er = Erasistratus; fl = floreat; G = Gaius; Ga = Galen; He = Herophilus; Mu = Foundation of Museum and library at Alexandria; Ma = Marinus; N = Numisianus; St = Straton.

observations. Thus the already ancient notion of pneuma as the substance of life needed to be found a place in any physiological account of the living body. The pulsation of the arteries seemed, as already noted, to be the sign of life. Thus, that pneuma should be located in the arteries that supplied all parts of the anatomy and caused the pulse made perfect sense.

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Alexandria and Hellenistic Psychophysiology The second reason for Praxagoras’ theory lies in the dissection technique that we saw was practiced in the Lyceum. This technique, as we noted in Chapter 1, caused arterial spasm forcing blood from the arteries into the veins. Consequently, in subsequent dissection the arterial system was largely empty and collapsed while the veins were engorged with blood. Thus, argued Praxagoras, the life-giving pneuma, which normally filled and distended the arteries, had escaped at death, leaving the arteries collapsed in on themselves. But it is still difficult to understand why Praxagoras disbelieved the everyday evidence of his eyes and insisted that the arteries in life contained pneuma and not blood. It seems that the answer to this conundrum lies in his association with Straton, the second successor (after Theophrastus) to Aristotle as director of the Lyceum. Straton of Lampsacus (340–270 BCE) was exactly the same age as Praxagoras but unlike him was a physicist rather than a physiologist. As a physicist he taught the Democritean philosophy of atoms moving in the void and was, moreover, a thoroughgoing materialist, much interested in the concept of the vacuum or void, and the ancient notion of horror vacui. It was possible, therefore, for Praxagoras to argue that, when an artery is cut, the pneuma immediately escapes leaving a void and is replaced, in life, with blood moving across from the venous system.4

Herophilus of Chalcedon (335–280 BCE) Herophilus was a slightly younger contemporary of both Praxagoras and Straton. As noted above, he seems to have been the first anatomist permitted to carry out detailed dissections of human bodies. Again we have little first-hand knowledge of his work and most of what we know derives from Galen’s voluminous writings.5 He is credited with naming a number of anatomical structures: the initial segment of the small intestine, for instance, easily distinguished from the rest, is about three handbreadths in length—12 fingers— hence, Latinized from Herophilus’ Greek, dodecadactylos. We know it as the duodenum. Similarly, the sensitive layer at the back of the eye seemed to him rather like a spider’s web. Hence he named it the amphiblestroides, the Latin translation of which is “retina.”

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Alexandria and Hellenistic Psychophysiology In his middle years Herophilus migrated from Chalcedon to Alexandria, where he was associated with his younger colleague, Erasistratus, in setting up the great medical school in the Museum. Here he made significant contributions to (p.32) the foundations of neuroscience. He seems to have been one of the first, if not the first, to distinguish nerves from blood vessels and tendons. He showed that a distinction could be made between motor (neura prohairetika) and sensory (neura aisthetika) nerves. He strongly contested the Aristotelian cardiocentric psychophysiology, maintaining that the brain and not the heart lay at the center (hegemonikon) of the system. He described many parts of the brain for the first time and argued that the soul resided in the ventricles—most importantly in what we now call the fourth. A structure in the floor of this ventricle seemed to him to resemble a pen’s nib and he named it accordingly and that name has come down to us, Latinized, as calamus scriptorius. It can still be found in 21st-century editions of Gray’s Anatomy. One other vastly important result of his anatomical labors is best described in the words of Galen’s commentary: “the sensory nerves which descend from the brain to the eyes and which Herophilus called conduits because they…display visible channels.”6 In fact, Herophilus was not the first to “see” the optic nerve as a hollow tube. Alcmaeon of Croton, as we saw in Chapter 1, was, according to Theophrastus, of the same opinion.7 The eye, he says, “sees by water and the fire in it.” The water, he believes, comes from the brain, along the hollow optic nerves, and is returned to the brain along the same nerves, this time carrying the fire or light that is before the eyes.8 This idea that the optic nerves were hollow, and the later Erasistratean notion that all nerves are hollow tubes, has resonated through two millennia until Leeuwenhoek and other microscopists showed it to be incorrect in the 17th century.9 One further opinion of Herophilus is worth noting. He believed that four forces motivated the body, not three. The first of these motivators, the nourishing soul, was located in the liver; the second, a thermal soul, was situated in the heart; the third, a perceptive agent, was located in the nerves; the fourth, the faculty of thought, inhabited the brain. Despite this distribution of motivating factors, it is clear that what we nowadays regard as the psyche is associated with the nervous system. In contrast to his great predecessor at the Lyceum, Herophilus’ psychophysiology is profoundly cerebrocentric.

Erasistratus of Chios (304–250 BCE)

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Alexandria and Hellenistic Psychophysiology Erasistratus, a pupil of Metrodorus, the son-in-law of Aristotle, is the last great physiologist in the early Alexandrian sequence. Nearly 500 years elapsed before a figure of comparable importance—Galen—emerged. This, of course, is not to say that for nearly half a millennium no work of comparative importance in anatomy/physiology was carried out, nor is it to say that figures of comparable intellectual power did not exist. It is only to say that if it was, and if they did, it and they have been lost in the wreckage of past time and the breakup of civilizations and city states. Erasistratus was a younger contemporary of Herophilus (Fig. 2.4) and his name has been darkened down the centuries, along with that of Herophilus, by reports that both were involved in the grisly process of human vivisection. Celsus, in the second century CE, writes that: And they [i.e., rationalist doctors] say that Herophilus and Erasistratus did this in the best way by far, by cutting open the criminals provided by kings from prison, and inspecting, while still alive those parts which nature had previously hidden…nor is it, as most people say, cruel that in the execution of criminals, and but a few of them, we should seek remedies for innocent people of all future ages.10 In spite of or, more probably, because of, this cruelty, Erasistratus’ contributions to physiology were immense. Indeed he is often regarded as the father of the subject. As the pupil of Aristotle’s son-in-law he must have been familiar with the work of at least the later Lyceum, although Aristotle himself had died nearly 20 years before his birth. Even so, his physiology, like that of Herophilus, is profoundly cerebrocentric. Although Erasistratus placed the brain at the center of his physiology, he shared and developed his colleague Herophilus’ interest in the cardiovascular system. He is remembered not only as a pioneering “neurophysiologist” but also for the discovery and correct interpretation of the bicuspid and tricuspid valves of the heart.11 Galen reports his discovery in the following words: “Each of these last mouths, as Erasistratus says in his description, is a channel of exit, one of them for the blood of the lung, the other for pneuma to the body at large…the heart itself expands like a brazier’s bellows, distends itself by its diastole.”12 This passage shows that, like Praxagoras, Erasistratus had been influenced by Straton of Lampsacus and that, like Praxagoras, he employed the latter’s ideas about the void and the notion encapsulated in the term horror vacui in his physiological system. The heart’s work is done at diastole not, as William Harvey was to demonstrate 2,000 years later, at systole. As the heart expands, both blood and pneuma are sucked into it: Nature abhors a vacuum!

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Alexandria and Hellenistic Psychophysiology Erasistratus’ central idea was that the anatomy of the body was formed not of cells (as we now think) but by the intertwining of three different sets of tubes. This, he thinks, is the case as far as the eye can follow it and by extension into the sub-visible microscopic domain. The notion that the anatomy is at root woven from fibers (not tubes) was in fact very long-lasting. It is to be found in the writings of 18th-century anatomists and only really disappeared (p.33) when the cell theory was developed in the middle of the 19th century.13

The three tubular elements in Erasistratus’ psychophysiology were arteries, veins, and nerves. These vessels branched again and again below the level of vision, plaiting and twining together to form the substance of the body’s tissues. Each of these three vessels contained a Figure 2.4: Detail of a woodcut depicting fluid: the veins blood, a Herophilus and Erasistratus by Lorenz nutritive fluid manufactured by Fries, 1532. (Courtesy of Wellcome the liver from the products of Library, London.) digestion; the arteries a more rarified fluid—the vital spirit (pneuma zootikon)—derived from the environing pneuma; and the nerves a yet more refined and subtle fluid—the animal spirit (pneuma psychikon)—distilled from the pneuma zootikon by the brain. Thus we see, once again, how the concept of pneuma pervades ancient thought. In the pre-Socratic tradition it first makes its appearance with Anaximenes (c. 585–c. 525 BCE) in the well-known fragment we have already quoted more than once, “As our soul being air holds us together and controls us, so does wind and air enclose the whole world.”14 In fact, as we noted in the prologue to this book, the concept of the breath of life far predates Anaximenes: it was common in deep antiquity and is well expressed by the Homeridae.15 With Erasistratus it is firmly bound into a detailed physiological system. Let us briefly review that system (Fig. 2.5).

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Alexandria and Hellenistic Psychophysiology Erasistratus agreed with Anaximenes that pneuma, an enlivening principle, is drawn into the lungs from the surrounding atmosphere. From here it made its way to the left side of the heart by way of the pulmonary vein. From the left heart it was distributed all over the body via the arterial system. We noted above that Erasistratus had made a close study of the cardiovascular system and that he was familiar with the major valves of the heart. This Praxagorean/ Erasistratean idea that the arteries contained pneuma was, like the notion that nerves were hollow tubes, destined to linger long in medical and physiological theory. Indeed the word artery, itself, originally signified “air-duct.” Arteries, indeed, were long conceived to originate in the lungs and trachea. As late as the 17th century we find Francis Bacon writing “The lungs…through the Artery, Throat and Mouth maketh the Voice.” [our italics]16 To the obvious point that the arteries must contain blood rather than airy pneuma because when they are cut blood spurts out, Erasistratus made the same reply that Praxagoras had made to his critics (see above). The pneuma zootikon, or vital spirits, in the arteries was distributed all over the body and, as Praxagoras had also taught, made the difference between a living and a dead body. This distribution was not, however, the rapid flow with which we are familiar today but conceived to be rather slow and sluggish. When the tide of vital spirits surged up the carotid arteries to the brain it lost itself in the cerebral substance and an ultimate refinement occurred, the results of which were secreted into the cerebral ventricles as pneuma psychikon or animal spirits. This subtle fluid flowed out through the hollow tubes of the nerves to be distributed all over the body. Thus, in conclusion, we can see that according to the Erasistratean system every part of the body was woven of three vessels, one containing a nutritive fluid (the blood), one containing an enlivening fluid (the vital spirit), and a third containing a psychic fluid (the animal spirit). After Erasistratus died in the middle of the third century BCE very little of importance in neurophysiology seems to have been achieved until the arrival of Galen in the second century CE. Despite the general movement of political power and culture westwards to Rome, the great medical school at (p.34)

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Alexandria and Hellenistic Psychophysiology Alexandria continued to exist and, no doubt, educated distinguished alumni. Few, however, left any traces in recorded history. A couple of names escape these dark ages. Galen writes that Gaius (fl.? 100 CE) and Eudemus continued neuroanatomical research and then, in the second century CE, nearly half a millennium after the foundation of the Museum, Numisianus and Marinus resurrected some of the anatomical brilliance of Alexandria’s early years.17 Numisianus is known to have instructed Pelops, Galen’s teacher, and Marinus, working in 120 CE, published important secondcentury works on anatomy, including neuroanatomy.

Galen (130–c. 216 CE) Claudius Galen (Fig. 2.6) was born in Pergamon in about 130 CE, the son of a wealthy architect with extensive intellectual interests, including philosophy, mathematics, astronomy, and literature. He was to retain this wide cultural interest throughout his own life: indeed, one of the enormous number of books he published had the title Quod optimus medicus sit quoque philosophus (The best physician must also be a philosopher).18 His father, in addition to being well read and intellectually ambitious, was also wealthy. (p.35)

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Figure 2.5: Diagram of Erasistratean physiological psychology. The left and right sides of the heart are separate. Both arteries and nerves contain pneumata. The arteries contain pneuma zootikon (vital spirit); the nerves contain pneuma psychikon (animal spirit). The movement of both types of pneumata and of the blood (manufactured from the food in the liver) was regarded as rather sluggish. All three fluids were understood to be totally consumed in the body’s tissues. (From Smith, 1976.)

Alexandria and Hellenistic Psychophysiology Pergamon at that time was a cultural and intellectual center with a library second only to that in Alexandria. It attracted thinkers from all over the Ancient World. His father thus saw to it that the young Claudius had the best education available and was fully part of a wide cultural circle. Ultimately, after a dream, he directed him into a medical career. The young Galen studied at many of the great centers dotted around the seaboard of the eastern Mediterranean and finished his training in his late 20s at the great medical school in Alexandria.

In 157 CE, at the age of 28, Galen returned to Pergamon as physician to the gladiators, and 5 years later, in 162 CE, he moved to Rome, where he enjoyed great success becoming physician, in turn, to the Emperors Marcus Aurelius,

Figure 2.6: Galen. From ‹www.livius.org/ a/1/greeks/galen.jpg›

Lucius Commodus, Lucius Verus, and Septimus Severus.19 In addition to these brilliant appointments Galen was, as mentioned above, a prolific writer. He is believed to be responsible for over 100 treatises, with a further 60 doubtfully his or almost certainly spurious. Indeed, Galen himself made an attempt to sort out this attributional problem by publishing a bibliography—De libris propriis— listing 124 texts. This gigantic output was based not only on his wide medical and anatomical experience but also on voracious reading. His intellectual position is usually regarded as eclectic. He belongs completely to none of the principal schools of ancient thought: he is neither Peripatetic nor Platonic, neither Stoic, nor Epicurean, nor Skeptic. He relied entirely neither on book-learning nor dissection nor experiment. In this sense, despite of the criticism he received 1,500 years later, when his system was replaced by the work of Vesalius, Harvey, Willis and many others, his approach is surprisingly modern.

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Alexandria and Hellenistic Psychophysiology In this book there is no room to review his ideas in full; we shall concentrate on his physiological psychology.20 In many ways he takes his cue from the system Herophilus and Erasistratus left half a millennium before. In one respect, however, his neurophysiology showed a great advance. He did not labor under the illusion that arteries were filled with pneuma. They contained no subtle wind but, in the words of a later and equally great physiologist, “the equivocal gore.”21 His reasons for dismissing the Erasistratean doctrine derived from impeccable observational and experimental evidence. He had tied the two ends of an artery and punctured the middle to show the indisputable presence of blood. Despite this, as indicated above, Galen’s system shared many of the features of that of his great predecessors (Fig. 2.7). Galen, like Erasistratus, conceived that a vital principle—pneuma—was absorbed from the circumambient air. It was absorbed principally via the lungs but also, as we shall see, to a lesser extent via the nasal passages. He had made a close anatomical examination of the minute ramifications of the pulmonary air passages and had concluded that “under normal circumstances pneuma passes from the [ramifications of the] trachea into the pulmonary veins, although in very small amounts.”22 He believed, with Erasistratus, that the blood itself was manufactured from the products of digestion in the liver. But, unlike Erasistratus, he had the beginnings of the idea of a pulmonary circulation. In other words, he maintained that blood from the right side of the heart made its way, although only very slowly, through anastomoses in the pulmonary system, to the left side.23 It was in passing through the convolutions of this system that it became charged with small quantities of pneuma, hence being transformed into the pneuma zootikon, or vital spirit. Galen also believed that the heart’s interventricular septum was penetrated by minute invisible pores. Small quantities of blood from the right ventricle were thus able to squeeze through into the left. It was left to Harvey some 1,500 years later to show that these pores did not exist. The 17th-century reappraisal was, however, revolutionary in another way, for Harvey’s work injected a huge new dynamism into cardiovascular physiology. The Erasistratean/Galenical system was, in contrast, sluggish in the extreme. Only small quantities of blood squeezed from the right side to the left side of the heart via the pulmonary anastomoses and via the invisible interventricular pores. It was a totally different system from that with which we are familiar today. Instead of a rapid forceful circulation, blood was moved by the heat of the “dark fire,” in the left ventricle, in a slow convectional current. (p.36)

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Alexandria and Hellenistic Psychophysiology The smoldering “dark fire” in the left ventricle caused the pneuma zootikon to be delivered via the arterial system to all parts of the body. One important route was via the carotid arteries to the brain. According to Galen the carotids terminated in the “retiform plexus” or, as it was later called, the rete mirabile, a plexus of vessels surrounding the stalk of the pituitary gland at the base of the brain. Unfortunately for Galen this plexus is not developed in humans or, for that matter, in the Pongidae, although it is well represented in oxen and other large domestic animals. In humans the part played by the rete is taken by the circle of Willis. Galen had obviously been doing his neuroanatomy on infra-human animals.

Galen’s dissections had revealed four ventricles in the brain—two anterior ventricles (our lateral ventricles), a middle ventricle (our third), and a posterior ventricle (our fourth). The two anterior ventricles and the posterior ventricle possess knots of intricately convoluted blood vessels—the choroid plexi —in their walls. These plexi, as we shall see, attracted Galen’s attention and play a crucial role in his system. Galen described one other structure, a structure

Figure 2.7: Galen’s physiological psychology. The text explains how pneuma psychikon is filtered from pneuma zootikon in the arteries into the cerebral ventricle and from there distributed by the nerves (not shown in this figure) to all parts of the body. Further explanation in text. From Smith, 1976.

that was destined to have a long innings in the history of neurophysiology. This was a worm-like structure that, he says, extends along the whole wall of the passage between the middle and posterior ventricle (our aqueduct of Sylvius, or iter) and which, he writes, regulates the flow of animal spirit between the anterior and posterior ventricles.24

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Alexandria and Hellenistic Psychophysiology (p.37) This structure was destined to play a significant role in psychophysiology for millennia. Galen is quite clear that it is not the pineal gland. He is quite clear that the pineal projects out from the roof of the aqueduct and not inwards as it would if it were to act as a valve. “Those versed in anatomy,” he writes, “have named it for its shape alone and call it the vermiform epiphysis [vermis superior cerebelli].” The significance of this structure was seized upon by Islamic physicians (Chapter 4) and through them it reappears in the writings of the great medieval theorists (Chapter 5). It has been argued that this supposed valve between the middle and posterior ventricles makes a final modern-dress appearance, though with a very different form and function, in Descartes’ 17th-century hydraulic neurophysiology. Galen believed that the blood, or pneuma zootikon, was refined by the intricate microanatomy of the rete (which he likened to a fisherman’s net) to form an enriched secretion (compare the filtration of pneuma zootikon in the intricate ramifications of the bronchii). This refined pneuma then passed through the substance of the brain and underwent a second distillation in the choroid plexi, located in the walls of the lateral and third ventricles, before being secreted from them into ventricles. This final secretion formed the pneuma psychikon and filled the ventricles. It can be seen that the neurophysiological system is in its general features very similar to that which Herophilus and Erasistratus had developed half a millennium before. Galen had, however, carried out a large number of experiments (many of them animal vivisections) to establish his ideas.25 One of these experiments involved ligating the carotid arteries. He found to his amazement that the ligation produced very little effect on the behavior, the probably desperate behavior, of the animal—usually a dog. How could this be? Galen concluded that there must be a second, supplementary, source of pneuma directly from the atmosphere through the nasal passages.26 This pneuma, after passing through the substance of the brain, would be secreted from the choroid plexi in the walls of the lateral ventricles.27 He probably assumed that this was particularly the case in animals with long sub-cerebral nasal passages such as dogs and goats.

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Alexandria and Hellenistic Psychophysiology The nerves, for Galen, took their origin either from the spinal medulla or from the fourth ventricle beneath the parencephalus, our cerebellum.28 He was satisfied that the optic nerve was hollow (as we have seen, this was the tradition since the time of Alcmaeon) and believed that the other nerves were also tubular but below the level of visibility. Although it is not fully clear whether Galen envisaged a flow of pneuma psychikon in these neural tubes or whether he supposed some other form of transport, the spirit (or its influence) was distributed to all parts of the body.29 Certainly, in some of his publications he sees the brain as a sort of pump. When he dissected the brain of a dead animal he found that it was significantly smaller than its cranial cavity.30 In addition, he observed during vivisection that the brain showed pulsatile movements and when the animal howled the brain bulged out of his incision. He concluded that these pulsatile movements sent the animal spirit down the motor nerves and sucked it back up sensory nerves: “As the heart relaxes and contracts to accommodate and eject its material,” he writes, “so the brain, when it needs to distribute pneuma psychikon contained in its ventricles to some parts of the body, sets the pneuma in motion.”31 Galen’s careful experimental approach led to a number of insights into neurophysiology. He was able to prove conclusively that the brain and not the heart was the source of sensations and motions. He was able, for instance, to show that certain specifiable parts of the body were paralyzed when different nerves were severed. He was able, furthermore, to demonstrate that it was the brain and not the heart that controlled the voice. He is said to have stumbled on this discovery by accidentally cutting the recurrent laryngeal nerve of a squealing pig. However, he followed up this piece of serendipity by examining the effects of carefully sectioning this nerve in a variety of mammals. Altogether, Galen’s experimental work conclusively established the brain as the source and center of sensation and motion and the nerves as its communication channels.32

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Alexandria and Hellenistic Psychophysiology Galen also carried out a fair number of animal vivisections in an attempt to discover the physiological role of the brain and its ventricles. He concluded that, so long as the substance of the brain was untouched, an animal’s behavior was hardly affected. He removed the dura mater and investigated the ventricles. By pressing down on each in turn he showed that the posterior ventricle (our fourth) was the most important. Destruction of this ventricle invariably led to the death of the animal.33 But he also noted that the mere opening of the ventricles was not fatal: the unfortunate animal remained alive, and if the incision was not too severe, and the wound healed, regained its normal behavior. The pneuma psychikon was not, then, to be confused with the soul, the principle of life, for if it were, the animal would irrevocably die. Rather, it was to be considered the soul’s instrument: it transmitted information about the world to the brain and the commands of the brain to the muscles. When it escapes from the opened ventricle, the animal is deprived of both sensation and movement. Both these faculties are restored when the wound heals and animal spirit is once more secreted into the sealed ventricles.34 The principle of life was thus to be found elsewhere; perhaps in the substance of the brain, not in its ventricles. This localization of consciousness in the brain’s substance rather (p.38) than in its cavities has, of course, like much else in Galen, a very modern ring. Galen’s understanding of the cerebral ventricles, obtained by dissection and experimentation, is physiological rather than psychological. The later notion that the three ventricles were associated with different faculties of the rational “soul”—imagination (anterior), ratiocination (middle), and memory (posterior)— does not appear in Galen’s extant writings.35 The rational soul, for Galen, was, as we have noted, to be found not in the ventricles at all but, mysteriously, in the brain’s substance.

Concluding Remarks With Galen we arrive at end of the first great period of neuropsychological research. We can see how over a huge period of time, some 500 years from the death of Aristotle in 322 BCE to the death of Galen in about 216 CE, neuropsychological thought gradually evolved from an airy speculation to a far more precise and anatomically grounded science. A “step-change” in this transition occurred very early, in the great medical school founded at Alexandria in the immediate aftermath of Alexander’s death, and was greatly deepened and expanded by the work of Galen at the end of the period.

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Alexandria and Hellenistic Psychophysiology Although Galen’s approach was in many ways recognizably “modern” with its emphasis on dissection, observation, and experiment, it can nevertheless be seen to be hindered by the persistence of more ancient ideas about the nature of things—in particular by the persistence of ancient notions bound up in the concept of pneuma, the “breath of life.” These ancient ideas, as we shall see, lingered on long after Galen and the demise of classical civilization and persisted into post-Renaissance times. But, in addition to the overriding influence of the ancient worldview, Galen’s work was ultimately limited by the technical resources of his times. There were no microscopes to examine the fine detail of anatomy, there was little in the way of physiological apparatus. The major outlines of Galen’s synthesis, though not his experimental and anatomical methods, formed the background of biomedical understanding for the next millennium. His concept of the origin and function of pneuma psychikon, or animal spirit, not greatly different from that of the great Alexandrians half a millennium earlier, lived on well into the 16th and 17th centuries CE. We take up this story in the next chapters of this book. Notes:

(1) The antikythera mechanism, so named because it was recovered from a shipwreck near the Greek island of Antikythera, seems to have been an “analogue computer” designed to predict the movements of the sun and moon. It was recovered from the wreck in 1901, and Michael Edmunds, who subjected the mechanism to a thorough study, writes that “the way the mechanics are designed just makes your jaw drop” and that he regards “this mechanism as being more valuable than the Mona Lisa” (Sample, 2006). See also Freeth, 2008, and Marchant, 2010, who points to a Babylonian influence. (2) Russo, 2004. See contrary reviews in Nature, 430, 614 (2004) and Physics World, 17(4 (2004)). (3) Smith, 1870, vol. 3, p. 516. For more about Praxagoras see Steckerl, 1958. (4) This suggests that Praxagoras was fully prepared to accept that invisible channels existed between the venous and arterial systems. This seems also to have been the understanding, as we shall see, of Herophilus and Erasistratus. (5) von Staden’s authoritative account of Herophilus and the beginning of the Alexandrian school of medicine should be consulted for further detail (von Staden, 1989). (6) Galen: On the usefulness of the parts of the body X, 12. (7) Kirk and Raven, 1971, p. 233. (8) Freeman, 1946, p. 137. Page 18 of 20

Alexandria and Hellenistic Psychophysiology (9) Van Leeuwenhoek, 1675, p. 378: “I took eight distinct Optic Nerves, and observed that after those nerves had been a little while cut off from the eye the filaments of which they were made did shrink up…And, upon this shrinking up, a little pit appears about the middle of the Nerve, and ’tis this pit in all probability, that Galen mistook for a cavity.” It may be, of course, that Galen, Herophilus, Alcmaeon, and other early anatomists took the cupping above the cribriform plate, or perhaps the central retinal artery that runs in the center of the proximal part of the optic nerve, to be the initial part of a tube. Leeuwenhoek’s work is reviewed further in Chapter 7. (10) Celsus, De medicina, vol. 1, p. 15. This is not the only report of this abominable practice, but the most explicit. These reports have frequently been contested, although somewhat unconvincingly. (11) Wilson, 1959. (12) Galen, De placitis Hippocratis et Platonis, Book VI, Chapter VI. (13) Albert Reimarus, the medical-student son of the famous 18th-century philosopher, wrote to his fellow student, Erasmus Darwin, describing anatomy as “unweaving the fiber-woof of life.” Quoted in King-Hele, 1999, p. 18. See also extended treatment in Chapters 11 and 12. (14) Kirk and Raven, 1971, p. 158. (15) See Prologue. (16) Bacon, 1626, p. 46, §199. (17) Rocca, 2002. (18) See Brian, 1979. Galen’s extant texts are collected in Kuhn, 1821-33; many of his works are also collected in French translation in Darenberg, 1845-46. (19) Further detail of Galen’s life may be found in Pearcy, 2010. (20) A detailed account of Galen’s work on the brain may be found in Julius Rocca’s 2003 monograph. Armelle Debru’s (1996) book on Galen also is worthy of mention, as it provides important information on Galen and breathing. (21) Harvey, 1628, p. 150. See Chapter 7. (22) Quoted in Siegel, 1968, p. 154. (23) Galen, On the Natural Faculties, 3, 15. (24) Galen, De usu partium (On the Usefulness of the Parts of the Body), 1, 491.

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Alexandria and Hellenistic Psychophysiology (25) Galen’s anatomical and experimental work on the brain is extensively reviewed in Rocca, 2003. (26) Galen, De usu respirationis, quoted in Rocca, 1997 pp. 222–223. This idea persisted for a millennium and is still to be found in Vesalius’ 1543 Fabrica. (27) Galen is ambiguous on this point; the experiment on the carotids was evidently very difficult to fit into his system. (28) Rocca, 1997. (29) In De locis affectis, Book 1, Chapter 7 (Siegel, 1968, pp. 31–32), Galen compared the transmission of the nervous power along nerves to the sudden strike of a ray of sunlight. This comparison turns up in many later writings, including Hunayn during the Islamic ascendency, Vesalius in the European Renaissance, and further on still, with Willis in the late 17th century. The comparison, on the other hand, may go back further even than Galen and derive from the neo-Platonic school of philosophy. (30) Galen, De anatomicis adminstrationibus (On anatomical procedures), Book IX, Chapter 2. (31) Galen, De placitis Hippocratis et Platonis, Book III, Chapter 8. (32) See Galen, De usu partium (On the Usefulness of the Parts of the Body). (33) Galen also notes that this can also be observed in the trepanation of men whose skull bones have been fractured (De placitis Hippocratis et Platonis, p. 442). (34) Galen, De anatomicis adminstrationibus (On Anatomical Procedures). (35) Rocca, 2003, p. 245; Todd, 1984, p. 107.

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Introduction

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.41) Introduction The second part of this journey through time and space will take us to a very different atmosphere. Thus far we passed through a scene in which the soul (psyche), which in Homeric times did little more than to go wailing down to the underworld immediately after leaving its body upon death, and then stayed forever in that place (see the Prologue), had become a busy multitasking mistress assisted throughout life by a complex organization of various pneumata or spirits. Already during Galen’s life, however, and more so following his death at around the turn of the third century CE, a social process that had started nearly 200 years earlier was gaining unexpected momentum. The Christian faith that originated in Judaea, a province in the distant Middle Eastern edge of the Roman Empire, had spread around the Mediterranean to become a fast-growing religious movement. Proselytism grew steadily despite constant persecution of the Christian protagonists, first by incensed Jewish leaders and then by worried or irate Roman emperors. This social phenomenon turned out to be so decisive for world history that chronologies are still counted with regard to its beginning, as either before (BCE) or within the Common Era (CE), taking the alleged year of Christ’s birth as the date of reference. The cultural, political, and economic consequences affected not only what people believed and how they behaved, but also shifted the focus of intellectual activity and, with it, the pace of scientific development, bringing it almost to a halt for a very long time.

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Introduction As an important tool of their strategy to survive and evangelize, well-educated Christian priests began to publish treatises about the main tenets of their creed, trying to delineate how they differed with regard to the dominating pagan views. Hence, an extensive literature produced in the first few centuries of the Common Era by these so-called Fathers of the Church, written initially in Greek and later on also in Latin, touched upon a number of subjects. Many of these texts include comments about ancient philosophers and their doctrines, and even verbatim quotations from works since lost, which are among the main sources and often the only references available today concerning the theses of some of the pre-Socratics, Stoics, and other philosophers of old. The major appeal of Christian teaching had to do with the possibility of resurrection and psychophysical immortality afterwards. Tales of heroes and other celebrities becoming immortal in flesh and spirit, once a certain god had rescued them from death, were common among the Greeks and other ancient peoples. Those cases were exceptions, however. Common individuals should at most expect survival of their soul alone, either for finding a new body to inhabit, as Plato and other Pythagoreans believed, or to await eventual fusion with the general pneuma of the cosmos, implying total loss of personal identity, as the Stoics taught. Epicureans would not grant even that, expecting and even hoping for just a full dissolution of the entire soul shortly after death. Christian preachers, on the other hand, were assuring that everyone would live forever in body and soul after Judgment Day. The ultimate destination—paradise or hell—would depend on whether one had honestly believed in Christ and behaved in this life according to his precepts. This pledge, which ever-greater crowds were accepting as true, opened a new dimension in the traditional controversy about body and soul. It was one thing to imagine, in the dazzling fourth century BCE, that a recently released soul leaves its previous body and then infuses itself into a new fresh one; it was quite another to conceive, in the ominous third century CE, how the dry, mostly powdered and often incomplete remains of a long-deceased person could at the end of time be rearranged to be animated again by its own old soul, while lacking an organization of several spirits to execute the different enlivening functions. As might be expected, therefore, a substantial part of the Patristic literature is concerned with soul and spirit, and their relation to the physical body, in attempting to explain that both components could in fact eventually come together again, either for perpetual bliss or to suffer endless torment. No satisfactory answers, other than invoking God’s almighty power, were offered in terms of accounting for this postmortem physiology. Moreover, the narratives lack technical considerations like those given in the treatises written by Galen and other ancient physicians of note, because the Church Fathers had humanistic rather than medical backgrounds, as well as an altogether different purpose. Page 2 of 8

Introduction Nevertheless, this rarely examined subject in the history of physiology is included in Chapter 3 of our book for two reasons. First, it clearly is a part of the protracted effort to understand just what is the place of spirit or spirits in relation to soul and body for producing the set of activities—sensory perception, control of movement, coordination of internal organs—known as animal life. Second, two of these Christian authors, namely Nemesius of Emesa and Augustine of Hippo, are highly influential in our story: one for advocating a successful and enduring “three cell” model of spirit-mediated cerebral processing of information; the other for shifting the research interest away from the body, focusing instead on the study of the far more important soul. As a consequence, European thinking about physiology froze for nearly a millennium. Luckily, the achievements of Greek and Roman science were not entirely lost during that period, thanks to the nearly simultaneous emergence of another great and prevailing civilization, Islam, which found value in what others (p.42) from earlier times had taught and written about nature, science, and medicine. In particular, Arab physicians turned to Aristotle for enriching their science, and to Galen for guidance in medical knowledge and practice, combining such ancient Western theories with their inherited cultural ideas and procedures. Some important names in the history of Western medicine are but crude Latin adaptations of the actual Arabic names, as for example “Joannitius” (Hunain IbnIshâq) and “Avicenna” (Ibn-Sīna¯), two eminent Arab physicians who lived in the long period while Europe was immersed in its so-called “Dark Ages.” Hence Chapter 4 follows this interesting detour, taking us to the Middle East and northern Africa—places from where, in time, ancient learning would one day begin to slowly spread back across the European continent. The last chapter of this section will explore this latter recovery. Intrigued and hesitant, the Christian world would receive the key to its scientific future from its centuries-long Muslim enemies. One after another, translations from Arabic into Latin, and later from Greek into Latin, brought before the eyes of incredulous European priests and monks the treasure accumulated by their own ancestors. Age-old works written by a certain “Philosopher” named Aristotle offered an unheard-of brilliant perspective of the natural world. Books by a great ancient physician named Galen revealed many secrets about the internal structure of the body and its mechanisms, thus far known only to the highly esteemed Middle Eastern practitioners.

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Introduction Eventually some of those western clerics, mainly Dominicans friars like Albertus Magnus and Thomas Aquinas, tried hard to meld these discoveries with the teachings of the Christian Church, thus inaugurating Scholastic philosophy with its renewed interest in nature’s intricacies, now presented as manifestations of God’s infinite wisdom. Recognizing that there was still much more to be learned, especially as plagues swept out of control through Europe, some new Italian schools of medicine cautiously allowed an occasional dissection of a human corpse in a search to understand more about the body. In the final part of Chapter 5 we shall review how this revival of human anatomy would show that Galen, and with him all the mainstream schools of medicine in the Islamic and Christian cultures for more than 10 centuries, had been wrong on a number of issues. Not the least of these is the assumption that the human brain should have at its base, like those of the bovines, a plexus of vessels known as the “miraculous network” (Latin, rete mirabile) where the vital spirit in the arteries was supposedly distilled into the more highly purified animal spirit. Even the 16th-century initiator of modern anatomy, Andreas Vesalius, as we shall see, frankly confessed that many times he had been led to show the existence of the rete mirabile in a bovine brain, presented as if it were human, just for not daring to contradict Galen. Leonardo da Vinci’s depiction of the true shape of the cerebral ventricles, where according to established theory still valid in the 15th century the animal spirit should be stored ready for use, also forms part of our story. The section closes by showing how increasing doubts about the reliability of ancient learning in different fields of natural science, from physics to medicine, at last began to shatter the blind confidence so far invested on Greek and Roman works. No one and nothing could be trusted anymore in relation to nature without first studying the objective world with fresh eyes. Partly or fully revisionist authors like Jean Fernel, Bernardino Telesio, and Francis Bacon, will serve us to illustrate this new attitude, which tradition likes to regard as “modern.” Nevertheless, as we shall see, spirits of all sorts, including the animal spirit, continued to find a comfortable niche and prospered in this skepticism-filled setting. It is undeniable, however, that a real rebirth of intellectual undertaking in all walks of life (i.e., a broad wave of Renaissance) was surging across Europe, and that in turn this uprush would trigger a spirit-dooming scientific revolution.

(p.43) Chronology

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Introduction

Science and Learning

Cultural Context 313 Constantine proclaims religious tolerance for Christians (Edict of Milan) 330 Foundation of Constantinople

c. 390 Nemesius: De natura hominis 410 Sack of Rome by Alaric and the Goths 430 Death of Augustine 622 Migration from Mecca to Medina (year 1 of Muslim calendar) 636 Death of Isidore of Seville 634 Completion of the Koran 638 Muslims conquer Jerusalem 711 Muslims conquer Iberia 732 Battle of Tours (or Poitiers) 800 Charlemagne crowned emperor 813–833 House of Wisdom (Baghdad) c. 850 Hunayn Ibn-Ishaq (Johannitius) translates Galen’s Art of Medicine c. 900 al-Ra¯zi (Rhazes): Kitab al-kabir, (Great Medical Compendium) c. 980 al-Majusi (Haly Abbas) publishes Kitab al-Maliki (Complete Book of the Medical Art) c. 1025 Ibn Sina (Avicenna) publishes a 14-volume encyclopedia al-Qânûn fī’l-tibb (The Canon of Medicine) c. 1050 Medical school established in Salerno 1066 Normans conquer England

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Introduction

Science and Learning

Cultural Context

c. 1077–98 Constantinus Africanus at Monte Casino publishes Latin versions of numerous Islamic texts, including Haly Abbas’ as the Pantegni 1099 First Crusade; Jerusalem taken c. 1125 Anatomica cophonis published in Salerno 1147 Second Crusade c. 1150 Gerard of Cremona translates Arabic works into Latin

c. 1150 Magnetic compass in use

c. 1170 First European windmills 1187 Muslims recapture Jerusalem 1190 Third Crusade c. 1200 Anatomy of Nicolai the Physician

1200 Fourth Crusade: sack of Constantinople 1210 Franciscan order founded 1215 Magna Carta 1258 Sack of Baghdad by Mongols

c. 1263 Albertus Magnus: De animalibus c. 1270 William of Moerbeke translates Aristotle and others from Greek 1274 Aquinas: Summa Theologiae c. 1285 Spectacles invented 1290 Marco Polo: Tales of China 1300 Arabic numbers in use

1300 Dante: Divina commedia

1316 Mondino: Anathomia corporis humani 1336 Petrarch ascends Mount Ventoux Page 6 of 8

Introduction

Science and Learning

Cultural Context 1337 Commencement of 100 Years War

c. 1340 First public dissections authorized in Italy 1346 Battle of Crecy 1347 Black Death 1348 Boccaccio: Decameron 1415 Battle of Agincourt 1453 Ottomans under Mehmed II capture Constantinople 1453 End of 100 Years War 1455 Gutenberg prints first Bibles 1454–7 Ucello: Battle of San Romano 1492 Muhammad XII expelled from Spain 1492 Columbus discovers a New World 1503 Gregor Reisch: Pearl of Wisdom 1503–4 Leonardo da Vinci: Mona Lisa 1505 Leonardo da Vinci demonstrates true anatomy of ventricles 1510 Raphael: School of Athens 1521 Berengario: Commentary on Mondino 1523 Titian: Bacchus and Ariadne 1538 Vesalius: Tabulae anatomicae 1542 Fernel: Physiologia 1543 Vesalius: Fabrica 1543 Copernicus: De revolutionibus (p.44)

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Biblical Anima-Spirit

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Biblical Anima-Spirit C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0003

Abstract and Keywords This chapter shows how the Jewish-Christian tradition, along with Greek philosophy, led to the creation of “Western thought.” It first studies the Jewish belief that the essence of each individual man, linked to spirit, is immortal. It then discusses the concept of resurrection and addresses the question of whether the true basic composition of human nature is composed of either two or three parts. The next two sections discuss the concepts of the spirit and soul and the soul and body, before it discusses early Christian physiology. This chapter also takes a look at the developments that occurred in the Mediterranean during the time and the concern over what “is written”. Keywords:   Western thought, resurrection, human nature, Jewish-Christian tradition, spirit, soul, body, early Christian physiology

And the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. Genesis 2:7

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Biblical Anima-Spirit Most accounts on the history of physiological subjects, including this one,1 never fail to tell us that the 17th-century French philosopher René Descartes abstained from sending to press in his lifetime the great treatise on the philosophy of nature, Le Monde. The reason was he did not “want to publish a discourse which had a single word that the Church disapproved of.”2 He was justifiably afraid of undergoing an ordeal analogous to that just experienced by Galileo, who stood trial by the Roman Inquisition on suspicions of heresy for having stated in print the Copernican notion that the Earth moves peripherally around a static sun situated at the center. Descartes’ book not only supported this view as an important element of his natural philosophy, but also included a chapter describing a novel hypothetical conception of the structure and function of the human body as a mechanism essentially independent from the soul. The selfsufficiency of the body can be so absolute, Descartes held, that the soul could be considered as being absent in non-thinking animals. The chances of infuriating the powerful Catholic Church were clearly much higher for Descartes than they had been for Galileo. In Western countries inheriting 20 centuries of Christianity we all intuitively understand Descartes’ dilemma—clearly not the “publish-or-perish” advice popular in our modern scholarly spheres, but rather a stern “publish-and-perish” warning (in more than a figurative sense) of the traditional European world. For centuries before Descartes, dissenting from the Church, especially in public, could be quite uncomfortable when not actually dangerous. Consequently, dogma set in and research disappeared. It is thus no wonder that, other than specialists in the period, science historians rarely bother to explain how those obstructive religious concepts so fiercely defended by the Church originated in the first place. Most long-scope historical overviews of scientific development do not give much attention in general to intellectual developments during medieval times. Readers are comfortably taken over a time bridge across more than 1,200 years of “Dark Ages,” straight from the cultural twilight in the late Hellenistic period, at the most, right up to the dawn of pre-Renaissance.3 Yet any long-term historical follow-up of a specific important idea in European civilization requires at some point consideration of Christian doctrine, especially when—as in this case—one is dealing with spirits. Since Christian views are themselves rooted in the Jewish cultural heritage, we need to insert here some discussion of how the Jewish-Christian tradition mixed with Greek philosophy to produce that peculiar combination known as “Western thought,” out of which modern science later flourished.4 This is, then, a good opportunity to glimpse at a little-trodden road.

The Power of Jehovah’s Breath

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Biblical Anima-Spirit The Jewish people entered the picture in Western history mainly after 333 BCE, when the Middle Eastern countries were engulfed by Macedonian-Greek power as a result of Alexander the Great’s successful military expedition into Asia. This landmark episode was followed by a long period of Hellenization of all peoples living in the vast territories conquered, a slow process that included the translation into Greek language of that collection of sacred and historical Hebrew writings that Christians later called the Old Testament. Hellenization was not easy in Palestine, however, mainly because of the explosive mix of the extremely traditionalist Jews, on one hand, and the harsh methods applied by the new Greek ruler Antiochus IV Epiphanes (c. 214–164 BCE), on the other. Restlessness finally led to the establishment of an independent Hebrew state that lasted for about a century, (p.46) until in 63 BCE the whole region became part of the widening Roman Empire under Pompey the Great (106–48 BCE). Into this complex setting two iconoclasts of Jewish stock would arrive who, independently and for completely different reasons, attempted to harmonize their beliefs with the dominant Greek philosophy they considered reasonable enough. In the first century of the present era Philo Judaeus of Alexandria (20 BCE–50 CE), fully appreciating the relatively ordered and systematic Greek approach to knowledge, but intimately convinced at the same time of his native faith, made consistent efforts to conciliate the two. Since Greek philosophy itself was far from being as unified as Jewish ideology, however, Philo arrived at somewhat strange intellectual chimeras that usually satisfied no one other than himself. He insisted—to conservative rabbis’ chagrin—that the Biblical narrative, especially the book of Genesis, was written largely in an allegorical sense so that it could be easily understood by the lay people. Writing in Greek, Philo says, for example, that the phrase expressing that Jehovah “breathed into” man’s nostrils5 means only that what “the Father and Ruler of all…breathed in was nothing else than a Divine breath that migrated hither from that blissful and happy existence for the benefit of our race, to the end that, even if it is mortal in respect of its visible part, it may in respect of the part that is invisible be rendered immortal.”6 This clearly Platonized interpretation of the Scripture, hardly canonical in Jewish lore, implies an afterlife in which personal identity survives as Socrates claimed to believe; but it also associates such identity with pneuma, something this Greek philosopher in particular would have laughed at, but which was later firmly established in Stoic views.7 Despite this confusing assembly, here we find an element that would have profound implications in Christian doctrine: the essence of each individual man, linked to spirit, is immortal.

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Biblical Anima-Spirit While Philo Judaeus struggled in Alexandria to frame the poetic accounts of the Bible within the reliable scaffolding of Greek thought, far away in Syria his somewhat younger coreligionist Saul of Tarsus (5 BCE–67 CE) underwent a road accident. While on his way to capture members of a new renegade Jewish faction in Damascus’ synagogues, he was suddenly blinded by a bright light coming down from the sky, which provoked his fall to the ground as he heard a voice asking him: “Saul, Saul, why do you persecute me?”8 After the invisible speaker identified himself as Jesus Christ, the very founder of that new apostatical sect, whom the Romans had recently killed by crucifixion, Saul changed sides and even his own name upon recovering sight 3 days later. Converted now to “Paul” and an ardent follower of Christ (Fig. 3.1), for the rest of his life he was fully committed to win adepts to this religious cause among both Jews and non-Jewish peoples alike around the Mediterranean. As it is well known, this quest inaugurated a new era. Not only was human spirit in fact divine breath and therefore immortal, as Philo wrote. Now Paul offered immortality of the body as well, since at the last trumpet sound

the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality.9 Thus death, the so-farunavoidable final defeat of everyone, would eventually be “swallowed up in victory.” Not a bad deal in exchange for a pious, love-filled life.

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Biblical Anima-Spirit Resurrection The promise that according to their behavior in terrestrial life the dead would rise and thereafter enjoy endless bliss in heaven—that is, as saints—or alternatively suffer endless torment in hell, necessarily meant re-animation of cadavers. There could hardly be any doubt that the efficient corpserising agent would once again be that which animated the first man—divine breath or spirit. According to Paul, “if the Spirit of Him that raised up Jesus from the dead dwelleth in (p.

Figure 3.1: Saint Paul Apostle (5 BCE–67 CE), formerly the Christian-persecuting Saul of Tarsus, became the main consolidating factor of early Christianity as a result of his indefatigable traveling and keeping an intense correspondence exchange with different communities around the Mediterranean. (Imaginary portrait statue of St. Paul’s by A. Tadolini, standing in front of St. Peter’s Basilica at the Vatican; detail of original color photograph by Matthias Trischler, with permission of the author, available at http://commons.wikimedia.org/wiki/ File:Vatican_StPaul_Statue.jpg.)

47) you, He that raised up Christ from the dead shall give life also to your mortal bodies through His Spirit that dwelleth in you.”10 This confidence on the resurrecting ability of God’s breath was not new in Jewish thought. The prophet Ezekiel, who lived approximately in the same epoch as the earliest Greek philosopher Thales, even provides a description of how disjointed anatomical parts can come together again by the power of divine breath. He tells of how the Lord once took him over to a large common graveyard and instructed him to summon the old remains there: O ye dry bones, hear the word of the Lord. Thus saith the Lord God unto these bones; Behold, I will cause breath to enter into you, and ye shall live: And I will lay sinews upon you, and will bring up flesh upon you, and cover you with skin, and put breath in you, and ye shall live…11 As soon as Ezekiel did as he was told to, strange things started to happen: there was a noise, and behold a shaking, and the bones came together, a bone to his bone. And when I beheld, lo, the sinews and the flesh came up upon them, and the skin covered them above: but there was no breath in them.12 Then the Lord instructed Ezekiel to give a final command: prophesy, son of man, and say to the wind, Thus saith the Lord God; Come from the four winds, O breath, and breathe upon these slain, that they may live…and the breath came into them, and they lived, and stood up upon their feet, an exceeding great army.13 Page 5 of 35

Biblical Anima-Spirit Early Christian intellectuals (i.e., mostly bishops contemporary with Galen who later became saints) considered resurrection as no more difficult and perhaps actually easier than animating a body newly formed from scratch the first time. Thus Athenagoras of Athens (c. 133–190), for example, says that if God brings the bodies of men into existence from their original elements, “He will, when they are dissolved, in whatever manner that may take place, raise them again with equal ease: for this, too, is equally possible to Him.”14 Athenagoras’ contemporary Irenaeus of Lugdunum (now Lyon, France; c.120–202), in turn, was among those who believed the second process would in fact be far simpler to achieve, because surely it is much more difficult and incredible, from non-existent bones, and nerves, and veins, and the rest of man’s organization, to bring it about that all this should be, and to make man an animated and rational creature, than to reintegrate again that which had been created and then afterward decomposed into earth…, having thus passed into those [elements] from which man, who had no previous existence, was formed.15 After all, in their view, human death is just the separation of an everlasting soul from its material body. Putting these two components together again for resurrection, then, is not big deal for Him who created both in the first place. Full resurrection of a person involves not only reconstitution and reanimation of the body, as it would be the case with an animal, but also complete recovery of the personality proper of a certain human soul. And it is indeed the divine source of the breath or spirit that makes the difference between man’s soul and mere spirit in brutes, like “the dumb cattle, whose spirits, not being composed of God, but of the common air, are dissolved by death”—we are told by the Roman Christian writer Lactantius (c. 260–330),16 tutor to the son of Constantine I the Great (272–337), the first Roman emperor to become a Christian convert (see below). Resurrecting cattle, of which body as well as spirit become lost upon total dissolution, one could imagine would present a double difficulty—not insurmountable either for God’s absolute powers, of course, but wholly unnecessary because discarnate people no longer require those beasts.

Spirit and Soul

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Biblical Anima-Spirit More of a problem was deciding just how the divine breath could animate the bodies under common circumstances, particularly because of a troubling question about whether the true fundamental composition of human nature consists of either two or three parts. As mentioned in the epigraph at the beginning of this chapter, according to Jewish-Christian belief the creation of man included just an earthy body and the breath of life coming directly from God himself, which turned the new creature into a living soul. For some reason, however, the second ingredient—divine breath—was not deemed as necessary for “every living creature that moveth,” since other animal species, from “creeping things” to “every winged fowl” to “great whales,” were created before man just by divine fiat.17 The classic explanation for this difference, as we saw above, was that insufflation of God’s own breath into Adam’s nostrils was a special distinction granted only to the human race. It was this unique privilege that accounted for man’s obvious superiority and set him apart from all other creatures. Still, there are only two components—a material body and divine breath or spirit—that make up human nature according to the account given in Genesis. Why was it, then, that Paul once wished farewell to the Christian inhabitants of Thessalonica referring to three parts with the words: “And the God of peace himself sanctify you wholly; and may your spirit and soul and body be preserved entire”?18 This three-part structure of man is resonant with the tripartite soul in Plato’s scheme, as well as with the three kinds of soul according to Aristotle,19 except that neither of these philosophers counted the whole material body in the sum. The parallelism is closer to conceptions of the two major schools of Greek thought in the contemporary (p.48) Hellenistic period. As reviewed in Chapter 1, the Stoic philosophers conceived the soul as consisting of several pneumatic parts, among which a centrally located commanding faculty (the hegemonikon) was distinguished.20 Similarly, the Epicurean soul includes two parts, a central animum and an extended animam, sharing a single nature.21 Accordingly, Paul’s reference to three components, “spirit and soul and body,” was well framed within common views in his time. The complication for later Christian thinkers arose from an underlying concern about deciding whether it is the spirit or the soul that comes directly from God, and how the original arrangement of the three parts would occur again in resurrection. An interpretation often given in modern times for Paul’s threeelement composite is that man as such is constituted of body and soul only, while Christians in particular include spirit too. In fact this might be the profound reason for baptism, because Paul also said referring to those in the new faith: “For in one Spirit were we all baptized into one body, whether Jews or Greeks, whether bond or free; and were all made to drink of one Spirit.”22

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Biblical Anima-Spirit Whatever the explanation accepted by each of today’s varied Christian churches, however, at their early beginnings as a single stalk the Paulist goodbye to the Thessalonians was a source of much discussion concerning the correct understanding of spirit (pneuma) in man. Tatian the Assyrian (c. 110–172), another early Father of the Church, recognized the coexistence of “two varieties of spirit, one of which is called the soul [psyche], but the other is greater than the soul, an image and likeness of God.”23 Yet for Tatian this does not seem to have been an exclusive attribute of man, for there are also “a spirit in the stars, a spirit in angels, a spirit in plants and the waters, a spirit in men, a spirit in animals; but, though one and the same, it has differences in itself.”24 Irenaeus, for his part, possibly uneasy with such a pantheistic account, devised a more complicated formula, conceiving that “the perfect man consists in the commingling and the union of the soul receiving the spirit of the Father, and the admixture of that fleshly nature which was moulded after the image of God.”25 He later explains, however, that there are three things out of which, as I have shown, the complete man is composed —flesh, soul, and spirit. One of these does indeed preserve and fashion [the man]—this is the spirit; while as to another it is united and formed—that is the flesh; then [comes] that which is between these two— that is the soul, which sometimes indeed, when it follows the spirit, is raised up by it, but sometimes it sympathizes with the flesh, and falls into carnal lusts.26 It is therefore the wayward soul, in its always difficult relationship with both the higher-rank spirit and the lowly body, that constitutes the main source of confusion about how the human person is actually integrated. Let us now hear from other voices in this context.

Soul and Body In Carthage, on the northern African coast (see Fig. 1.2), the more plainspoken Tertullian (c. 145–220) attempted to stay clear from such subtleties in interpretation. Writing profusely about Christian matters in Latin (rather than in Greek) apparently before anyone else, he stated in a treatise dedicated to the problems encountered in trying to understand the human soul: Whenever, indeed, the question is about soul and spirit, the soul will be (understood to be) itself the spirit, just as the day is the light itself. For a thing is itself identical with that by means of which itself exists.27

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Biblical Anima-Spirit Inevitably, however, Tertullian would also get trapped in problematic definitions when distinguishing between the two. Thus, for example, even though both soul and spirit were obviously linked to respiration, he maintained “the soul to be breath and not the spirit, in the scriptural and distinctive sense of the spirit; and here it is with regret that we apply the term spirit at all in the lower sense, in consequence of the identical action of respiring and breathing.”28 Semantic hairsplitting becomes even more convoluted in a five-book polemic addressed to a heretic named Marcion: …we must explain the nature [qualitas] of the soul. We must at the outset hold fast the meaning of the Greek scripture, which has afflatus [pnoen], not spirit [pneuma]. Some interpreters of the Greek, without reflecting on the difference of the words, and careless about their exact meaning, put spirit for afflatus; they thus afford to heretics an opportunity of tarnishing the Spirit of God, that is to say, God Himself, with default. And now comes the question. Afflatus, observe then, is less than spirit, although it comes from spirit; it is the spirit’s gentle breeze, but it is not the spirit. Now a breeze is rarer than the wind; and although it proceeds from wind, yet a breeze is not the wind. One may call a breeze the image of the spirit. In the same manner, man is the image of God, that is, of spirit; for God is spirit. Afflatus is therefore the image of the spirit. Now the image is not in any case equal to the very thing.29 Nevertheless Tertullian is of special interest to us here for, contrary to other apologists of what each of them believed to be the correct analysis of Christian doctrine, he did not accept the common neo-Platonist notion that soul and/or spirit are incorporeal. He argued emphatically that (p.49) only a body, however subtle, can act upon another body;30 therefore the soul, in order to actuate the animal body, must be corporeal and closely related to respiration, as the Stoics taught. A learned man, Tertullian was not only fully abreast of the Gospels and writings by all the major philosophers, but also well read on current medical matters. He is one of the ancient sources reporting, even if in an outraged tone, the experiments of that “butcher [Herophilus], who cut up no end of persons, in order to investigate the secrets of nature”31 (discovering the existence of a nervous system, among other things). He cites also Soranus (first–second century CE), an eminent physician from Ephesus, as an authority to back up the claim of the corporeality of the soul for it is even nourished by corporeal aliments; that in fact it is, when failing and weak, actually refreshed oftentimes by food. Indeed, when deprived of all food, does not the soul entirely remove from the body?32

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Biblical Anima-Spirit In his staunch conviction that the soul—if not the whole human spirit—is corporeal, the Carthaginian Church Father stood near the standard medical theory of his time, but without much company among other fellow theologians. A clear distinction between spirit (pneuma) and soul (psyche or anima) was necessary for all Christian literature, either theological or medical, and this consensus was eventually reached by the fourth century. Thus, in a commentary to a partial translation of Plato’s Timaeus produced around the year 320, the Christian writer Chalcidius (fourth century CE) reports approvingly about those who “have brought many things very clearly into the light”—Alcmaeon and Herophilus among them—“namely that there are two narrow passages containing natural spirit [naturalem spiritum], which pass from their seat in the brain, wherein is situated the highest and principal power of the soul, to the cavities of the eyes.”33 The soul seems therefore as having been promoted here to the higher rank, whereas spirit in several varieties would be gradually charged with specific functions, as we will see next.

Early Christian Physiology Later in the same fourth century Nemesius (fl. 390 CE), at that time the bishop of Emesa in western Syria (see Fig. 1.2), came up with a still more thorough analysis of how man is actually constituted, so that his place in the context of the creation could be adequately understood in Christian terms. Almost nothing is known about the author himself, other than his ecclesiastical position, in part because for many years his treatise De natura hominis (On the Nature of Man) was mistakenly attributed to the more famous contemporary bishop and later saint Gregory of Nyssa (c. 335–394). Successively translated into several languages, including Arabic in the ninth century by the Nestorian Christian scholar Hunain ibn Ishaq (known as Joannitius among European scholars at the time), and of course eventually Latin, Nemesius’ book remained to be, and still is, a much valued source of the knowledge that was current in the Roman Empire by the late fourth century. The text makes it clear that the author was a highly educated man who in addition was well versed on medical matters, even more so than Tertullian had been. Nemesius’ treatise is especially relevant to our story here, not only because being written by a high-echelon churchman it formally introduced Greek physiology into Christian conceptions, but more particularly because it is the earliest extant source in which specific psychological faculties appear associated to definite cerebral locations. The text discusses three hollow spaces in the head (Fig. 3.2) —later called cellae or “cells,” as we shall see in Chapter 5—, all filled with psychic pneuma and each in charge of a particular role: “The organs of imagination are the frontal cavities of the brain, the psychic pneuma within them, the nerves from them soaked with the psychic pneuma and the apparatus of the sense organs.”34

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Biblical Anima-Spirit A few pages later this notion of thorough impregnation with psychic pneuma is expanded to the entire nervous system in order to explain the functions of the most extensively distributed of all senses: So how can touch belong to the whole body, when we say that sensations are from the frontal cavities of the brain? Surely it is obvious that the sensation of touch supervenes when nerves descend from the brain and divide themselves over the whole body. Yet since often, when our foot hits a thorn, the hairs on our heads immediately shiver, some have thought that the affection, or the sensation of the affection, is sent upwards to the brain. Yet if this account were true, it would not be the part that is cut that suffers pain, but the brain. It is therefore better to say that the nerve is the brain, for it is a part of the brain, which has psychic pneuma all throughout itself, just as iron that has been heated in the fire contains the fire; well, for this reason, then, whenever a sensitive nerve grows, this part has a share in sensation because of this, and it becomes sensitive.35 Behind the frontal cavities of the brain that are “the origin and roots of sensation” as well as the organs of imagination, there lays the organ of thought that consists of “the central cavity of the brain and the psychic pneuma within the cavity.”36 Finally, the “organ of memory, too, is the posterior cavity of the brain, which they call the cerebellum and the enkranis, and the psychic pneuma within it.”37 The anteroposterior alignment of these cavities is appropriate for carrying on the flux of mental operations in an orderly way, so that “the faculty of imagination hands on things imagined to the faculty of thought, while thought or reasoning, when it has received and judged them, passes them on to the faculty of memory.”38 (p.50)

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Biblical Anima-Spirit It is important to note here that, as stated in Nemesius’ writing, these three supreme organs in charge of the higher faculties of the nervous system are all composed of the respective cavities and the psychic pneuma within them. Rendered to Latin this fluid is animalem spiritum (animal spirit)—that is, the spirit related to the anima, instead of just “natural spirit” like that contained in the optic nerves according to Chalcidius (see note 33 above). This is but an instance of the numerous terminological inconsistencies about the physiological spirits, as found in texts coming from an age in which the blending of Greek science with Christian doctrine was still in the process of being established.

The actual origins of the above assignment of specific faculties to the brain cavities, which is an important development in the history of neurophysiology that would remain universally accepted up to the Renaissance, are unclear.39 It was not a matter of pure speculation for Nemesius, since he seems to have drawn upon empirical observations “to demonstrate whether this is the state of affairs, lest we should seem to believe what is being said without having a good reason for it.” And he goes on: The most adequate demonstration is gained from the activity of the parts. If the frontal cavities are damaged in any way the senses are impaired but thought remains unharmed. If the central cavity alone suffers thought is overthrown but the sense-organs continue to preserve their natural [power of] sensation. If both the frontal and the central cavities suffer, reason is damaged together with the senses. But if the cerebellum suffers, memory alone is lost together with it, without sensation or thought be harmed in any way. But if the posterior suffers together with the frontal and central ones, sense, reason, and memory also are destroyed, in addition to the whole creature being in danger of perishing.40

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Biblical Anima-Spirit This passage is closely similar to another text from a contemporary, perhaps somewhat earlier medical writer named Posidonius of Byzantium (middle to late fourth century CE). There we find a description of the mental symptoms associated with inflammation of the meninges (phrenitis, from phren, “mind” in ancient Greek language) in various regions of the brain: Phrenitis is an inflammation of the membranes surrounding the brain during

Figure 3.2: The three cavities within the brain called “cells” (“cellae”, little rooms) or ventricles (little bellies), supposedly containing psychic pneuma, are the sites responsible for the main higher faculties of the central nervous system, according to the long-lived scheme discussed by Nemesius, bishop of Emesa in western Syria (fl. 390 CE). In this model the frontal cavity, which receives connections from all the sense organs and where therefore the center of all sensations or common sensorium (sensus communis) is located, resides also the faculty of imagination. The cell in the middle (cogitativa) is where thought or reason takes place, while the posterior cavity

acute fever, causing insanity (memorativa) is reserved for keeping and loss of reason.…There information already processed. This are several different kinds of model was destined to endure as the phrenitis, but the following official theory for the following 10 three are most important. centuries and beyond (see Chapter 5). Either only imagination is (Woodcut engraving from Illustrissimi affected and reasoning and philosophlet theologi domini, Venice, memory are spared; or only 1496, figure 13; Wellcome Library, reasoning is affected and London, cat. M0000435.) imagination and memory are spared; or imagination and reasoning are affected and memory is spared. Furthermore, loss of memory due to febrile diseases usually destroys the faculties of reason and imagination as well. A disorder of the anterior part of the brain affects only the imagination; a disorder of the middle ventricle leads to aberration of reason; a disorder of the posterior part of the brain near the occiput destroys the faculty of memory, usually together with the other two.41

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Biblical Anima-Spirit Since the extant works by Galen do not go beyond ascribing sensory functions to the frontal part of the brain and mental activities to the brain substance in general, rather than to its parts, it may be that the precise localizations mentioned by Nemesius and Posidonius are a product of clinical interpretations collected during the century and a half following Galen’s death. Now Galen himself, we have (p.51) seen before,42 concluded that the pneuma contained in the cerebral ventricles is not the soul proper, but rather an instrument of it.43 For Nemesius too psychic pneuma is a substance different from the soul, which the bishop argues at length to be incorporeal, battling in the process all and every one of the previous philosophers who held contrary views on this subject.44 Let it suffice for our purpose to mention only his argument that “the soul, if it is nourished, is nourished by the incorporeal, for it is studies that nourish it,”45 whereas the “nourishment of the psychic pneuma is by breathing in alone: for some portion of air is drawn into the heart through its expansions.”46 Nemesius’ insistence on the incorporeality of the soul derives from such a property being, in his model, a key condition for a seamless functional union with the body. For this bonding is not just an attachment or mere juxtaposition, nor a mixture like that of wine with water that destroys the identity of both components. Instead the soul is unified with the body “as the sun by its presence transforms the air into light, making it have the form of light, and light is unified with the air, mixed with it without being compounded.”47 This thorough pervasion of the air by light without actual mixing, since by night or in a darkened space the air remains as pure as it was before illumination, is possible because light is incorporeal. In a similar fashion, the soul, being incorporeal, and not circumscribed in place, occupies as a whole the whole of its own light and of its body, and there is no part to which it gives light in which it is not present as a whole. For it is not controlled by the body, but itself controls the body; it is not in the body as in a vessel or a wine skin, but rather the body is in it.48 In Nemesius’ Christian view, with a little help from the neo-Platonist metaphor of light for the soul but interpreted differently than by Tertullian,49 the choice is solved beyond further question in favor of Galen’s conclusion of the psyche as being other than the pneuma psychikon. Psychic pneuma or animal spirit—the spirit of the soul—although intimately imbued with the soul and located for the most part at its headquarters within the brain, is at its root a corporeal substance; exceedingly subtle, to be sure, but not incorporeal like the soul itself.

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Biblical Anima-Spirit In neatly separating psyche from psychic pneuma with clear and vigorous arguments reflecting the most advanced philosophical and medical positions of his time, Nemesius provided an opportunity for scientific inquiry to move on while Christian beliefs were kept safe in a haven of faith. In retrospective, this step was analogous to the highly celebrated one achieved by Descartes in separating soul from body, as discussed in Chapter 6. Had the Emesan bishop’s contribution been recognized or even scrutinized in his age, as was that of the French rationalist in the mid-1600s, Christian physicians might have followed in Galen’s footsteps. They would probably have developed medical knowledge much more in the following centuries, like a number of brilliant devout Christian polymaths started to do 12 centuries later and beyond, during the fecund intellectual upsurge known as the Scientific Revolution and the Enlightenment.50 For spirit would have been seen as a bodily component, like blood or muscles, in charge of carrying out chief physiological operations through purely material interactions worth investigating. History wanted otherwise, however. Not only was Nemesius’ work mistakenly attributed to another bishop for nearly 200 years, as mentioned above, but in addition the tide of the times extinguished the conciliatory opportunity offered by some of his ideas. The product of his eclectic effort was translated into Latin several times because of its anthropological interest, but it did not have much influence on shaping the emerging Christian dogma. Moreover, neither Nemesius nor Tertullian or Lactantius, some of the better-read and articulated apologists for early Christianity, were even awarded sainthood in gratitude for their forceful intellectual wrestling on behalf of the faith. Instead, along came a formidable figure who would sweep everyone aside and under in the relentless job of settling for good the proper and rightful foundations of the Church.

The Coming of a New Age This was a time in which the Mediterranean world was changing rapidly. Continued struggle for political power had gradually destabilized the vast Roman Empire, offering an opportunity that was seized by its many enemies for challenging and decreasing its nearly absolute dominance. Furthermore, governing such a large territory from Rome in the center of Italy had become increasingly difficult. As a result, by the second half of the third century the administration of the empire was divided into two regions, west and east. Next, in 330 the above-mentioned emperor Constantine I (Fig. 3.3) formalized this divide with the establishment of a second capital or “new Rome” in what had been the old Greek city of Byzantium, henceforth called Constantinopolis—the city of Constantine—or Constantinople (today’s Istanbul). In time this ancient urban center would become the capital of the Byzantine Empire.

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Biblical Anima-Spirit These political developments in turn had profound cultural implications. Constantine, crediting the Christian god for his victories in decisive military battles, became a sympathizer of the so-far-semi-clandestine but nevertheless growing religion. Already in 313 the emperor had issued the Edict of Milan that granted religious tolerance—in practice freedom of cult—to all citizens, eventually becoming himself a convert to Christianity who would ask for baptism on his deathbed. Such liberty, however, encouraged open discussion and different opinions on theological matters, thus fostering the emergence of all sorts of dissenters or heretics. The efforts of the Christian Church to counter such rapid disintegration of doctrinal unity would be finally championed (p.52)

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Biblical Anima-Spirit by Aurelius Augustinus (354–430; Fig. 3.4), bishop of the North African Roman town of Hippo Regius (see Fig. 1.2) at the turn of the fifth century, who later on would become Saint Augustine. In contrast to Nemesius, about whom virtually nothing is known as a historical presence, Augustine’s life is one of the best documented of late antiquity, thanks to his detailed Confessions and other biographical accounts written about him by his fellow churchmen. It is clear that his mother raised him as a Christian from early childhood, even though his father was a pagan, and that he nevertheless joined the Manichaean religion in his early youth. Interested in Latin literature, Augustine obtained a private scholarship to study rhetoric in Carthage, where he engaged in a 13-year affair with a young woman who bore him a son. During this time he made a living and supported his family as a teacher of rhetoric, first in Carthage and then in Rome, eventually accepting a prestigious chair in Milan.

Figure 3.3: Constantine I the Great (272– 337), Roman emperor, proclaimed religious tolerance across the empire in 313, effectively ending the persecution of Christians; moreover, he eventually became a convert himself. (Roman bronze head, part of a colossal statue from the fourth century CE, now exhibited at the Capitolini Museums, Rome; public domain picture, freely available by courtesy of Jastrow at http:// commons.wikimedia.org/wiki/ File:Head_Constantine_Musei_Capitolini_MC1072.jpg.)

While in Italy, Augustine became increasingly disappointed with Manichaeism and inclined instead to neoPlatonic authors such as Plotinus. This process led him into a deep personal crisis over beliefs that ultimately culminated—under the persistent influence of his mother and Ambrose, the bishop of Milan—in his conversion to Christianity. Following his baptism in 387, and the deaths of both his mother and his son, a reluctant Augustine was ordained a priest in Hippo, where he later became the local bishop and produced his truly monumental writings.

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Biblical Anima-Spirit The Key Is in the Words Concerned about education of the people, especially the young, Augustine developed his own theory and practice of teaching and started to write tirelessly, occasionally touching on medical subjects. He was not as clear about anatomical matters as the slightly older Nemesius, but knew that “the medical writers” had pointed out the existence of three ventriculi within the brain, which he summarizes:

Figure 3.4: Aurelius Augustinus, bishop of Hippo Regius in Northern Africa (354– 430), later known as Saint Augustine, hammered out the foundations of Western Christian theology as it survives largely intact still today. He urged followers to focus attention on the everlasting soul, rather than on the corruptible body, thus helping to discourage continued biological research. (Line engraving by P. Isselburg after an imaginary portrait by G. Gortzius, in which the bishop is depicted as arguing with an unseen interlocutor; Wellcome Library, London, cat. V0031644.)

One of these, which is in the front near the face, is the one from which all sensation comes; the second, which is in the back of the brain near the neck, is the one from which all motion comes; the third, which is between the (p.53) first two, is where the medical writers place the seat of memory.51 Augustine’s medical sources were apparently different from those consulted by Nemesius, for no cerebral ventricle in charge of reasoning or thought occurs in the Hipponian bishop’s model. At any rate, how the mental faculties are distributed among the various cavities within the head seems to be of secondary importance to him, since a few lines below he adds: The soul, however, acts on these parts of the brain as on its organs. It is not the same thing as they are, but it vivifies and rules all parts, and through them it provides for the body and for this life in virtue of which man was made a living thing. Significantly, therefore, it would appear that for Augustine reasoning is a faculty of the ruling soul itself, having little to do with the brain, which nevertheless is as it were, the heaven of the body. From this source come the rays which go forth out of the eyes, and from this center slender ducts go out not only to the eyes but also to the other senses, namely, to the ears, the nose, and the palate, making the sensations of hearing, smelling, and tasting possible. Moreover, they say that the sense of touch, which is all over the body, is directed from the brain also through the medulla of the neck and that of the bones to which the backbone is connected, and that from there tiny channels [i.e., nerves] making sensation possible are spread throughout all parts of the body.52 Page 18 of 35

Biblical Anima-Spirit On the other hand, that Augustine was not too familiar or in agreement with Galen is evident, for example, from his asking about “the use of those veins wherein air [aeris], instead of blood, circulates, which they call the arteries.”53 The good Church Father was not aware, or did not accept, that two centuries earlier Galen had demonstrated that arteries contain blood, just like veins.54 And there were a number of other things about the body that “the soul” was quite ignorant of, such as from what part of the body that which they call the ήγεμονιkόν [hegemonikon] (the authoritative part of the soul, the reason) exercises its universal rule, whether from the heart or from the brain, or by a distribution, the motions from the heart and the sensations from the brain, —or from the brain, both the sensations and voluntary motions, but from the heart, the involuntary pulsations of the veins; and once more, if it does both of these from the brain, how is it that it has the sensations, even without willing, while it does not move the limbs except it wills?55 Accordingly, although every one of these operations is ultimately carried out by the soul, she does not necessarily know how such operations are in fact executed, just like birds fly even though they know nothing about aeronautics. Special training at a medical school is needed to understand the mechanisms of the body. But then, inquires Augustine, Why should only a very few know why all men do what they do? Perhaps you will tell me, because they have learnt the art of anatomy or experiment, which are both comprised in the physician’s education, which few obtain, while others have refused to acquire the information, although they might, of course, if they had liked.…But this is a very important question which I now ask,…how is it that we can count our external limbs, even in the dark and with closed eyes, by the bodily sense which is called “touch,” but we know nothing of our internal functions in the very central region of the soul itself, where that power is present which imparts life and animation to all else, —a mystery this which, I apprehend, no medical men of any kind, whether empirics, or anatomists, or dogmatists, or methodists, or any man living, have any knowledge of?56 Advice follows immediately: “And whosoever shall have attempted to fathom such knowledge may not improperly have addressed to him the words we have before quoted, ‘Seek not out the things that are too high for thee, neither search the things that are above thy strength.’”57

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Biblical Anima-Spirit True to his own counsel, Augustine did not care much about lacking information or details concerning the corruptible body. His attention was focused on understanding the everlasting soul. Still, proper comprehension of the latter implied, of course—again—a careful interpretation of Apostle Paul’s words about man being composed of spirit, soul, and body.58 And this was no easy task. When arguing the point with a junior theologian, the old master at first dismisses the problem as “much more a question of names than of things,”59 because though there is certainly something in the soul (i.e., that “by which we reason and understand”) since Paul also appears to refer to this part as “mind,”60 the complete entity “is also designated with equal propriety ‘soul.’” A few lines later Augustine grants, however, that elsewhere Paul distinguished clearly between spirit and mind, as when preaching about the difficulties of praying in different languages: “For if I pray in a tongue [i.e., a language unknown to me], my spirit prayeth, but my understanding is unfruitful.”61 Evidently Augustine, always an accomplished rhetorician though one who admittedly did not read Greek, gave considerable thought to the problem posed by semantics and translations of terms he deemed to be of capital importance for (p.54) his evangelizing mission. “Spirit” was possibly his major trouble, for the situation then was no different than it is today if we are asked to distinguish between soul and spirit. Augustine’s confusion becomes obvious when reading his lengthy discussion of that passage in the book of Genesis (2:7) that originated the complication, in which he goes into a bewildering analysis. For our present purpose it is worth quoting here just the following excerpt, where our author explains that

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Biblical Anima-Spirit in this passage where it is said, ‘And the Lord formed man dust of the earth, and breathed, or inspired, into his face the breath of life;’ the Greek has not πνευμα [pneuma], the usual word for the Holy Spirit, but πνοή [pnoé], a word more frequently used of the creature than of the Creator; and for this reason some Latin interpreters have preferred to render it by ‘breath’ rather than ‘spirit.’ For this word occurs also in the Greek in Isaiah chapter vii, verse 16 where God says, ‘I have made all breath,’ meaning, doubtless, all souls. Accordingly, this word πνοή [pnoé] is sometimes rendered ‘breath,’ sometimes ‘spirit,’ sometimes ‘inspiration,’ sometimes ‘aspiration,’ sometimes ‘soul,’ even when it is used of God. Πνευμα [Pneuma], on the other hand, is uniformly rendered ‘spirit,’ whether of man, [quote and reference] or of beast, [quote and reference] or of that physical spirit which is called wind, [quote and reference] or of the uncreated Creator Spirit [quote and reference]. In all these quotations from Scripture we do not find in the Greek the word πνοή [pnoé] used, but πνευμα [pneuma], and in the Latin, not flatus, but spiritus. Wherefore, referring again to that place where it is written, “He inspired,” or to speak more properly, “breathed into his face the breath of life,” even though the Greek had not used πνοή [pnoé] (as it has) but πνευμα [pneuma], it would not on that account necessarily follow that the Creator Spirit, who in the Trinity is distinctively called the Holy Ghost, was meant, since, as has been said, it is plain that πνευμα [pneuma] is used not only of the Creator, but also of the creature.62 When at last the Church Father comes to conclusions, just on this point, the answer is not theological or anthropological but referred to relativism in the usage of language (i.e., rhetorical). He maintains that we understand that Scripture used these expressions in its ordinary style so long as it speaks of animals, that is, animated bodies, in which the soul serves as the residence of sensation; but when man is spoken of, we forget the ordinary and established usage of Scripture, whereby it signifies that man received a rational soul, which was not produced out of the waters and the earth like the other living creatures, but was created by the breath of God. Yet this creation was ordered that the human soul should live in an animal body, like those other animals of which the Scripture said, “Let the earth produce every living soul,” and regarding which it again says that in them is the breath of life, where the word πνοή [pnoé] and not πνευμα [pneuma] is used in the Greek, and where certainly not the Holy Spirit, but their spirit, is signified under that name.63

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Biblical Anima-Spirit Playing with words became handy, too, when dealing with the explanations of certain strange biological facts. On a certain occasion while Augustine was with a group of young students in Italy, it happened that one of them, upon watching a centipede or millipede that crawled nearby, cut the small creature in half with a stylus. Immediately, to general amazement, “both parts of the body moved away from the cut in opposite directions with a swift movement of the feet and with as much energy as if they had been two distinct animals of the same kind.”64 Severing each of these halves into more fragments produced again a similar result, as if all those animal parts “had been separately born, and that each was living an independent life.” This phenomenon touched on the difficult problems of the actual extension of the soul within the body and of its divisibility. Augustine’s teaching on this subject was categorical: the soul, being incorporeal, has no physical dimensions as material bodies do. Hence, having no extension in space, the soul is not divisible in separate portions either. On the other hand, it was inconceivable that those animal fragments, like Augustine had observed with severed tails of lizards, would continue to move by themselves in the absence of soul. At that embarrassing juncture the puzzled master theologian offered an undisclosed tricky answer to satisfy the understandable curiosity of the youngsters, probably a sleight-of-hand reply he was later hesitant to tell about. He could have resorted, at least provisionally, to Aristotle’s conclusion that any of such animals “is constructed like a continuous body of many separate living beings.”65 Nevertheless, the proposition of a series of souls acting coordinately together in a single body would have been too risky for Augustine even to mention. Still, years later he had at last found a satisfactory explanation for the abstruse prodigy of the multi-severed centipede, and the best way of making it understood was with a verbal example—an abbreviation: For instance, just as that worm as a whole occupied more space than any part of it, so a greater span of time is taken up in saying “Lucifer” than if one were to say only “Luci.” Hence, if this latter “lives” in virtue of its meaning, in the diminution of time brought about by the division of that sound, while the meaning itself was not divided —for not the meaning, but the sound, was extended in time— then we should judge in the same way of the worm with its body cut to pieces: that, although a part, by the simple fact that it is a part, lives in a smaller space, still the soul is not at all divided, nor has it been reduced in a reduced space, notwithstanding that it simultaneously dominated all the members of the whole living body, when they were extended over a larger space. The soul, you see, occupied not space, but the body which it controlled.66

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Biblical Anima-Spirit (p.55) How is this control executed? Earlier in the same book, when considering animal movements after an introductory explanation of how inert stones respond to forces applied to them, we learn that “the soul’s impulse uses sinews [nervis] like so many thongs to move the weight of the body,” so that “what is called strength is made up of an impulse from the soul and a sort of mechanism of the nerve sinews [nervorum quodam machinamento] and the weight of the body.”67 The following eight chapters deal with subjects related to sensory input, including a discussion of the definition of sensation and how vision operates, where we read that “Sight extends itself outward and through the eyes darts forth far in every possible direction to light up what we see.”68 No doubt Augustine was an astute, hard-to-beat debater, and he put this gift to good use in order to face his immense task. Like other Christian writers at the time, he applied all of his best efforts to consolidate canonical doctrine in response to twisted interpretations or to criticism from pagan intellectuals, with Galen being among them.69 This objective required conciliating the huge body of Scriptures written by widely different authors in many diverse historical settings, an undertaking that involved everything from harmonizing the Gospels with each other, up to explaining the apparent contradictions between the Old and the New Testaments. The outcome of these intricate compromises had in turn to hold firm, as best as possible, in front of current scientific views as the Fathers of the Church often amateurishly tried to understand them. In addition, all of this had to be done while watching carefully to make sure that no fissures were left vulnerable to what the clerics regarded as heresies (i.e., deviations from the allegedly true Christian tenets), either past, present, or foreseeable in the future. These guardians of the faith all shared the same goals, though they did not necessarily agree with each other on every point, nor contributed to the common objective with equal loads of work. Indeed, none of them came even close to matching the massive and exquisitely crafted output of Augustine, a feat considered since antiquity as nearly miraculous in itself, for it was believed that nobody could possibly read, let alone compose, so many books in a lifespan— even using all days and nights.70

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Biblical Anima-Spirit Understandably, once the impressive and painstakingly balanced construction seemed finished, no one wanted to touch it anymore. Preserving the edifice intact became a necessity, if the faith was to survive the attacks continuously received on multiple fronts. Nevertheless, unavoidably this was still a building made of words, for words were seen as the key to understand everything, and with good reason. Starting from the narration of the very origins of the world and of humankind as contained in the book of Genesis—and hence obviously revealed by none other than Jehovah himself—and all the way up to Christ’s teachings, transcendental truth was set in the words of God. No wonder that the Gospel of the Apostle John opens up by saying: “In the beginning was the Word, and the Word was with God, and the Word was God.” In this view it is indeed language—inner to oneself, spoken, or written for others—that more than anything else distinguishes man from animals, the divine attribute granted exclusively to humans among all mortals on Earth. The study of language itself is, therefore, the second most exact route to true knowledge; the first one being, of course, direct illumination by the Interior Teacher (i.e., God). With this in mind, let us now conclude this chapter by reviewing the work of another significant prelate who, 200 years after Augustine, looked hard into the origins and meanings of words.

Truth Is in the Words Concern about what “is written” was not only religious in origin, however. The accelerating decline of the once-mighty Western Roman Empire, which concluded with its official demise half a century after Augustine’s death, had a deleterious effect on the Latin language too. The better-educated citizens of the day, among whom the Christian churchmen were certainly outstanding, felt a growing need to fix the exact meaning of terms. This was perceived as a cultural exigency if the Holy Scriptures and the exegetical treatises by Augustine and other founding fathers, as well as the best legacy of selected pagan sages, were to be saved from utter confusion as the years and centuries continued to go by. Most of those scholars shared an honest belief that rescuing the actual significance of words would recover the deep truth of the writings where they were used. Thus many authors, with many different perspectives, produced a number of compilations and philological treatises, equivalent to what today we call dictionaries and encyclopedias. Consequently, in attempting to defend and preserve the true religion, learned Christian clerics in the sixth and seventh centuries helped to transmit ancient knowledge to the future generations.

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Biblical Anima-Spirit A pertinent example of such philologists is Isidore, Archbishop of Seville (c. 560– 636; Fig. 3.5) and eventually promoted also to sainthood, albeit long after his death. He was born at a time when the Western Roman Empire had crumbled to the point that barbarians of various denominations had invaded its territories and lived freely within them. As part of this process, Germanic tribes called Visigoths came from the north and swarmed the Iberian Peninsula, where Isidore’s family lived in a southern province. These were Hispano-Romans and thus Catholic, prominent enough for the elder brother to become the bishop of Seville, a post that Isidore later inherited. Apparently a reserved man with few friends, Isidore read and wrote through most of his episcopate. His huge erudition has impressed historians enough to prompt them to dub him variously as “the Pliny of his age” and “the last sage of the ancient world.” Undoubtedly he was well acquainted with both Christian scriptura and pagan litteratura. While many Christian authorities believed that much of the stormy social and political climate was largely due to pollution of feeble minds by what still remained of heathen writings, the Sevillian Archbishop, like Augustine, approached and appreciated ancient knowledge on its own terms. He found in it valuable information worth being rescued, preserved, and (p.56) presented in a Christian perspective for the wide, heterogeneous public at large.

Isidore was quite prolific and versatile as an author, with a veritable encyclopedic profile. Apart from the usual theological commentaries upon the Scriptures, plus some historical studies, and in the line of a common literary genre, Isidore also composed several large compendia of words, discussing their origins, differences, and proper meanings. The most representative of those is the 20-volume Etymologies covering virtually every field of knowledge in his day, a trove that we will use as a reference here.

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Biblical Anima-Spirit Many of the explanations given in this work sound incredible and even ridiculous, in a way that can hardly be justified by simple naïveté in an age of rapid cultural dissolution. This lack of uniformity in the quality or exactness of the Isidorian etymologies has been a matter of much discussion among experts. It is likely that, when at a loss to find the true derivation of a particular term, Isidore looked instead at its current understanding by the people, rather than inserting the “origin unknown” cliché of modern

Figure 3.5: Isidore of Seville (c. 560– 636), like many authors who lived at the time when the Roman Empire was crumbling, attempted to preserve classical culture and knowledge in systematic catalogs and other written compendia. His approach was to provide the origins and meanings of words, thus creating encyclopedic works like his Etymologies, in which a number of glimpses of concepts current in his age about the body and the soul–spirit are found. (Detail of line engraving by an unknown artist, in which an imaginary portrait of the bishop shows him while listening to a dove that represents the allwise Holy Spirit, the Christian version of

dictionaries. Additionally, it is the World Pneuma in Stoic philosophy; possible that he sometimes just Wellcome Library, London, cat. fantasized about the most V0032212.) probable of the imaginable possibilities. Whatever its reliability, the Etymologies remained for centuries a popular and widely used source for quickly obtaining encapsulated information about almost everything. Books IV and XI of the Etymologies, in particular, are of interest to us here. They include sections with detailed descriptions of medical practices and of human anatomical parts and their functions, as they were generally understood at beginning of the seventh century. In this comprehensive treatise Isidore states that: The most important part of the body is the head, caput; it has been given this name because all sensation and nerves [nervi] take their beginning thence, and because every principle of life springs therefrom. All the senses are centered there and, in a certain manner, it plays the part of the soul itself which takes thought for the body.71 Thus, for example, vision, which “is more vigorous than the other senses and is superior, or faster…is closer to the brain, whence all things proceed.” Indeed, “Some people affirm that seeing takes place either by an external ethereal light or an internal lucid spirit which come through delicate passages from the brain and after they have penetrated the coats of the eyes, come out into the air where they then give sight, being mixed with other similar matter.”72

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Biblical Anima-Spirit As for the anatomy relevant for us here, we may note that from the head and through the nape “the cerebrum is directed in a straight line to the spinal cord as through a channel for the brain;” part of the latter is in effect “carried through them [the vertebrae] by a long passageway to other parts of the body.”73 The reader is informed too that “Epilepsy, epilemsia, is named because hanging over the mind, it equally also possesses the body…[and] arises whenever the black bile happens to develop in excess and is turned in its course to the brain.”74 Basic neurology is therefore reasonably well covered for a broad source of general information about nearly everything. Here Isidore seems to endorse the Platonist/Galenic conclusion that the soul is located somewhere in the head. Nevertheless, now in a peripatetic or Aristotelian vein, elsewhere we are told that “life, that is, the soul, is centered” in the heart; accordingly “the praecordia [anterior parts of the chest] are the places near the heart by which sensation is perceived, and are called the praecordia because there is located the source, principium, of the heart and of cogitation.”75 Furthermore, Isidore reports, it is said “that the human heart is the first part of the body to be formed, because in it is all life and wisdom.”76 Accordingly, neither the readers nor apparently the author himself could tell where, whether in the head or in the breast, one can find the (p.57) center of the soul and therefore the source of life, sensation, cogitation, and even wisdom. Further, Isidore, like Augustine or Tertullian and others, could not evade getting entangled in the soul–spirit conundrum. Thus we read that “the soul [anima] is so named because it lives; [whereas] the spirit [spiritum] is named either because of its spiritual nature, or because it imparts breath in the body.”77 Yet both terms can be taken to express different aspects of a poly-functional faculty that “When it gives life to the body, it is the soul [anima]; when it wills, it is the mind [animus, i.e., courage]; when it knows it is the intellect [mens]; when it remembers it is the memory [memoria]; when it judges correctly, it is the reason [ratio]; when it breathes, it is the vital spirit [spiritus]; when it perceives anything, it is called sensation [sensus].”78 In a separate work where the precise meanings of apparently synonymous terms are discussed, Isidore comments approvingly about “learned men” who have distinguished between “soul” and “spirit.” Reportedly they saw anima as “life, presiding over the body’s sensation and motion,” whereas according to them spiritus is “whatever energy and rational potency” the soul has, making man an animal that excels over other animals, and stirring up “mortal man for the goal of an immortal life.”79

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Biblical Anima-Spirit It is this last interpretation that prevailed in the long term; the soul (anima) being considered as a vivifying factor present in humans as well as in beasts, hence the latter may be properly called “animals.” Spiritus, on the other hand, is exclusive to God, humans, and other creatures (angels, demons, and the like). That is, except when—following the straight translation from the Greek pneuma —one was referring to tenuous and invisible physiological fluids in charge of specific functions in animal bodies, including those of humans. These agents were also “spirits,” though of a different sort, not to be confused with “Spirit.” Despite their commendable intentions, therefore, the Church Fathers and other contemporary compilers ultimately muddled the allegedly univocal understanding of the very words of most importance for their quest. The soul, neither Platonic nor Aristotelian, with its main residence alternating now in the head and next in the heart, and being identified with, as well as differentiated from, spirit, became a wizard of metamorphosis, perpetually wandering up and down within its inhabited body, as best suited for the subject at hand. In turn spirit, a unique conscious and rational effluence from God, but also the motive power driving animal respiration (among other chores, like carrying sensory and motor information throughout the body), remained a handy multitasking device. Nevertheless, apparently nobody was troubled at the time by the total ambiguity and lack of semantic congruence of those terms, just as no one is now when “spirit” is happily entered into play to mean either the essence of a person or document, someone’s mood, an attitude shared by a team or by a whole epoch, as well as a distilled liquor or other volatile liquids. Nor probably were those people who lived at the entrance of the so-called Dark Ages much concerned that memory, instead of being safely kept always within the posterior cavity of the brain as Nemesius had postulated, and necessary as it evidently is for experienced reasoning, could sometimes be diffused in an ill-defined thoracic region near the heart where wisdom was often said to be seated. Now this is no different either from when in our own day a neurology professor insists that his or her students should know all the anatomical structures of the encephalon “by heart,” or a rejected lover complains about having a “heart broken with sadness,” to mention just some well-known modern examples.

Into Darkness and Later

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Biblical Anima-Spirit True or false, merely supposed or even imaginary, the definitions contained in Isidore’s bulky assemblages constituted, as mentioned above, handy reference sources for quick consultation of data on innumerable things. Consequently they were widely read throughout the Middle Ages, contributing greatly to secular general culture and worldviews for nearly a thousand years. Still, the huge and delicately balanced cathedral of words sheltering Christian education remained as flimsy and unsteady as ever before. Disagreements among Scriptural statements should be mandatorily accommodated as the Church Fathers had already indicated, rather than questioned or, worse still, disputed. Unconditional acceptance of what “was written,” especially in texts by Augustine, grew to become a necessity if the flock was to stay manageable. Deliberately or inevitably, dogmatism froze independent reasoning to the point that free thinking was nearly extinguished in the Western world. In fact, none of the available literature adequately addressed the fundamental conflict between Christian teaching and the scientific outlook of man—that is, that the human soul or spirit must be intrinsically different from, even though complementary to, the material body in the total person. No other living thing could possess a similar animating principle, as many pagans, even if otherwise reasonable and well educated, believed. And it was quite clear that those two components making up a human individual were also very different from each other in a pragmatic futurist perspective, because while the body becomes disintegrated and turns to dust soon after death, the spiritual soul, being an image and effluvium of its divine artificer, is everlasting. Studying and understanding the soul was therefore of paramount priority for anyone’s longterm interests. Even for the sake of the ultimate destination of the body, once it rises again to the call of the trumpet at the end of time, the soul came first. Thus, caring for the soul, rather than the body, was life’s main business in every sense. At the individual level the goal was of course salvation, and from the collective point of view not human knowledge but human behavior is what counts. The balanced conception of human nature inherited from the Greeks was thus gradually eroded as Christianization of the ancient world advanced, with most of the attention being now focused only on the soul. Introspection, rather than dissection, is what was called for. As a result, (p.58) all anatomical and physiological research gradually slowed down almost to a halt. Indeed it virtually stopped, except for a few contributions from some Christian physicians active in the Middle East, and from a lineage of Arab thinkers in the great Islamic empire that developed from about Isidore’s death up to about the middle of the 12th century.80

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Biblical Anima-Spirit By Galileo’s and Descartes’ time the Church was no longer a marginal, peaceful but beleaguered brotherhood trying to survive under the boot of Rome, but a colossal multinational organization attempting to maintain its rule over the world from its impressive headquarters at Rome itself. Having already grown and rooted deeply for over 1,200 years after Augustine, and managing now the will, trust, and fear regarding the afterlife of a large majority of citizens in all European countries, plus those in their vast new possessions abroad, the Roman Catholic Church had become a formidable political and economical power with as many terrestrial as celestial interests. Yet, congealed in uncompromising rigidity, its internal theoretical consistency had not improved, being as vulnerable to independent critical reading as in its remote beginnings. The Vatican, still shaken by the large recent wounds inflicted by the Lutheran, Calvinist, and Anglican secessions, only increased its defensive authoritarian stance. Thus, after having been persecuted, the Church had become a persecutor. Its freshly reinforced ideological police, the Inquisition, permanently screened communities in search of any development that was potentially threatening. Every new finding or proposition for a better understanding of the world was immediately suspicious. Those that might imply some correction of what “was written” were definitely guilty of heresy, for changing a word was sure to lead to a large-scale revision with unpredictable consequences for established doctrine. In this intellectual and political climate, to suggest that the Earth—God’s children’s home—is not at the center of the cosmic scenario, or that animals have no anima, was clearly asking for serious trouble. Galileo decided to take the risk, with consequences, and Descartes preferred better not to. But before we turn to Galileo, Descartes, and the Early Modern period, let us consider first what the Islamic culture and later Christian philosophers had to say about animal spirits and equivalent or related concepts. Notes:

(1) See Chapter 6. (2) Descartes, 1633, Letter to Marin Mersenne (see Gaukroger, 1995, p. 291). (3) A rare and important exception to this practice is Michael Frampton’s study (2008) on theories of voluntary motion in the ancient and medieval periods of Western science, in which part of the story covered in this chapter is presented, albeit with a different focus and interpretation. (4) The most authoritative examination of how the Greek scientific notion of pneuma evolved to become the Christian religious doctrine about spiritus in late antiquity continues to be that of Verbeke, 1945. (5) Genesis 2:7; see this Chapter’s epigraph.

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Biblical Anima-Spirit (6) Philo, On the Account of the World’s Creation Given by Moses, §46 (trans., Colson and Whitaker, 1991, pp. 106–107). For a more complete analysis of Philo’s interpretation of pneuma see Bréhier, 1950, pp. 133–135. (7) See for example Eusebius, Evangelical preparation 15:20, 6 (trans., Long and Sedley, 1987, p. 318). For a brief discussion about Stoic views in this connection see Chapter 1. (8) Acts of the Apostles 9:1–6. (9) Paul, Corinthians 1, 15:51–54. (10) Paul, Romans, 8:11. (11) Ezekiel 37:5–6. (12) Ibid., 7–8. (13) Ibid., 9–10. (14) Athenagoras, On the Resurrection of the Dead, 3 (trans. Pratten, in Roberts and Donaldson, 2001, p. 150). (15) Irenaeus, Against Heresies V, 3: 2 (trans. Roberts and Donaldson, 1995, p. 529). (16) Lactantius, Divine Institutes, II, 13 (trans. Fletcher, in Roberts and Donaldson, 1995, p. 62). (17) Genesis 1:20–25. (18) Paul, Thessalonians 1, 5:23. (19) See Chapter 1. (20) See Chapter 1; also the second–third-centuries Church Father Tertullian (see below), A Treatise on the Soul, 14 (trans. Holmes, in Roberts and Donaldson, 1995a, p. 193), and Aetius 4.21.1–4 (trans. Long and Sedley, 1987, pp. 315–316). (21) See Lucretius, On the Nature of Things, III: 136–144 (trans. Rouse/Smith, 1992, pp. 198–199). (22) Paul, Corinthians 1, 12:13. A formal analysis of Paul’s conception of pneuma in relation to Stoic views can be found in Engberg-Pedersen, 2000, pp. 157–166. (23) Tatian, Address to the Greeks, 12 (trans. Ryland, in Roberts and Donaldson, 2001, p. 70). (24) Ibid. Page 31 of 35

Biblical Anima-Spirit (25) Irenaeus, Against Heresies V, 6: 1 (trans., Roberts and Donaldson, 1995, p. 531). (26) Ibid., p. 534. (27) Tertullian, A Treatise on the Soul, 10 (trans. Holmes, in Roberts and Donaldson, 1995a, p. 190). (28) Ibid., 11 (Ibid., p. 191) (29) Tertullian, Five Books Against Marcion, II, 9 (trans. Holmes, in Roberts and Donaldson, 1995b, p. 304). (30) Tertullian, A Treatise on the Soul, 6 (trans. Holmes, in Roberts and Donaldson, 1995a, pp. 185–186). (31) Tertullian, ibid., 10 (Ibid., p. 189); for Herophilus see Chapter 2. (32) Ibid., 6 (Ibid., 186). (33) Chalcidius, Commentary upon Plato’s Timaeus 246 (trans. Longrigg, 1998, p. 169; see also Lloyd, 1975). (34) Nemesius, On the Nature of Man 6, p. 56 (trans. Sharples and van der Eijk, 2008, pp. 101–102). (35) Ibid., 8, p. 64 (Ibid., pp. 111–112). (36) Ibid., 12, p. 68 (Ibid., p. 118). (37) Ibid., 13, p. 69 (Ibid., p. 121). (38) Ibid. (ibid.) See also Chapter 5; for a discussion of theories on the brain ventricles see Manzoni, 1998. (39) For compact reviews of this subject see Finger, 2000, pp. 53–54, and Rocca, 2003, pp. 245–247. (40) Nemesius, Nature of Man 13, pp. 69–70 (trans. Sharples and van der Eijk, 2008, p. 122). (41) Aëtius of Amida’s Medical Books 6.2 (vol. 2, p. 125 Olivieri; quoted in Nemesius, Nature of Man [trans. Sharples and van der Eijk, 2008, n. 607, p. 121]). (42) See Chapter 2, and Rocca, 2003, pp. 196–199. (43) Galen, On the Use of Breathing 5, 7 (see Furley and Wilkie, 1984, p. 131).

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Biblical Anima-Spirit (44) Nemesius, Nature of Man 2, pp. 16–38 (trans. Sharples and van der Eijk, 2008, pp. 51–77). (45) Ibid., p. 19, 2 (Ibid., p. 55). (46) Ibid., 28, p. 90, 21 (Ibid., p. 163). (47) Ibid., 3, pp. 40–41 (Ibid., pp. 81–82). (48) Ibid., p. 41, 6–9 (Ibid., p. 82). Italics as in the source. (49) See note 27 above. (50) See Chapters 6 and following. (51) Augustine, The Literal Meaning of Genesis, Book VII, 18, §24 (trans. Taylor, 1982, vol. 2, p. 18). (52) Ibid., 13, §20 (Ibid., p. 15). (53) Augustine, A Treatise on the Soul and its Origin, Book IV, 6 (trans. Holmes and Wallis, 1995, p. 356). The translation’s rendering that the blood “circulates,” instead of simply “flows,” is of course a gross anachronistic oversight in the English version, for circulation of the blood was discovered by William Harvey only in the 17th century (see Chapter 7). (54) See Galen, Whether Blood is Naturally Contained in the Arteries (in Furley and Wilkie, 1984). (55) Augustine, A Treatise on the Soul and its Origin, Book IV, 6 (trans. Holmes, 1995, p. 357). (56) Ibid., 7 (Ibid.). (57) Ibid., 8 (Ibid.). (58) See note 18 above. (59) Augustine, A Treatise on the Soul and its Origin, Book IV, 36 (ibid., p. 369). (60) Paul, Romans 7:25. (61) Paul, Corinthians 1, 14:14. (62) Augustine, The City of God, Book XIII, 24 (trans. Dods, 1995, pp. 259–260). (63) Ibid. (Ibid., p. 260). (64) Augustine, The Greatness of the Soul, Chapter 31, §62 (trans. Colleran, 1978, p. 90). Page 33 of 35

Biblical Anima-Spirit (65) Aristotle, Progression of Animals, 7, 707b2–3 (trans. Farquharson, in Barnes, 1995, vol. 1, p. 1101). (66) Augustine, The Greatness of the Soul, Chapter 32, §68 (trans. Colleran, 1978, pp. 96–97). (67) Ibid., Chapter 22, §38 (Ibid., p. 59). Original Latin terms within brackets not included in the source quoted here. (68) Ibid., Chapter 23, §43 (Ibid., p. 66). Original Latin terms within brackets not included in the source quoted here. (69) For examples see Walzer, 1949. (70) Isidoro de Sevilla, Etymologiae Book VI (On Books and Ecclesiastical Crafts), 8: 3 (trans. Oroz Reta, 2004, pp. 572–573). (71) Ibid. Book XI (On Man and Monsters), 1: 25 (trans. Sharpe, 1964, p. 40). Original Latin term within brackets not included in the source quoted here. (72) Ibid., 20, 21 (Ibid., p. 39). (73) Ibid., 61, 95 (Ibid., pp. 42, 44–45). Explanatory brackets not included in the translation quoted here. (74) Ibid. Book IV (On Medicine), 7: 5 (Ibid., p. 58). “Epilemsia,” probably a corrupted term in wide use at the time since the correct one is also given immediately before in this passage, is only one of several synonyms used by Isidore for this disease. (75) Ibid. Book XI (On Man and Monsters), 1: 116, 119 (Ibid., p. 46). Explanatory brackets not included in the translation quoted here. (76) Ibid., 143 (Ibid., p. 48). (77) Ibid., 1: 10 (Ibid., p. 38). Original Latin terms within brackets not included in the source quoted here. (78) Ibid., 1: 13 (Ibid., p. 39). Note that the adjective “vital” qualifying “spirit” in the English translation of this paragraph is not found in the original Latin text, being thus a debatable interpretation of the translator. Original Latin terms within brackets not included in the source quoted here. (79) Isidore, Libri duo differentiarum II, 98 (Ibid. p. 28). (80) See Chapter 4.

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The Islamic Ascendancy

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

The Islamic Ascendancy C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0004

Abstract and Keywords This chapter studies the emergence of Islam, a civilization that found value in previous works and teachings on nature, medicine, and science. It shows that Arab physicians referred to the works of Aristotle and Galen to help improve their science and guide them through medical knowledge and practice. This chapter shows a renewal in anatomical investigation and studies Islamic medicine and science. Keywords:   Islam, Arab physicians, Aristotle, Galen, science, medical knowledge, medical practice, anatomical investigation, Islamic medicine

Seek knowledge, even if you have to go all the way to China. The Prophet Muhammed It grieves me to oppose and criticize the man, Galen, from whose sea of knowledge I have drawn so much…Although this reverence and appreciation will and should not prevent me from doubting, as I did, what is erroneous in his theories. al-Rāzi (Rhazes) (quoted in Masood, 2009, p. 100)

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The Islamic Ascendancy Rome was sacked many times, but never more completely than in 410 CE by Alaric and the Gothic horde. The Western Empire struggled on for a few more years until the last emperor, Romulus Augustulus, was deposed by his own mutinous troops in 476 CE. The Eastern Empire, centered on Byzantium (Constantinople, Istanbul) persisted, however, for nearly another millennium before finally falling to the Islamic army of the Ottoman Turks in 1453. The city, however, retained its central importance as the capital of the Ottoman Empire until that empire itself fell in the early 20th century. It was then replaced as the capital of Turkey by Ankara. Although Galen, as we saw in Chapter 2, was the last great medical figure in classical antiquity, medicine and medical inquiry did not, of course, totally cease after his death early in the third century CE. The Eastern Empire, as noted above, persisted for a thousand years after the fall of Rome. Yet conditions were not conducive to much further scientific development. The intellectual life turned inward, away from the unsatisfying things of this world, to the hope of a better world to come. The fathers of the Byzantine church showed the same conviction as those of their Roman brothers: scientific work was of secondary importance compared with theology and the religious life. Indeed, it has been suggested that Romulus Augustus himself, after being deposed as emperor, founded a long-lasting monastery. The vital impulse of science having been diverted into the bitter arguments of theology or the quietude of monastic life, all that remained was to preserve the writings of antiquity. Commentaries and analyses of the works of Aristotle, Plato, and others were written by many Byzantine scholars and philosophers. Furthermore, knowledge of Greek science and philosophy spread eastwards from Byzantium into the lands of the Middle East, as far as what is now Pakistan. This eastward diffusion had, of course, started many centuries before the fall of the Western Empire. Alexander the Great, Aristotle’s star pupil, had carried Greek culture eastwards in the fourth century BCE. This diffusion of Greek thought had never really ceased. At his death in 323 BCE Alexander had left upwards of 10 Alexandrias scattered across the Middle East. It was, moreover, not just warfare that seeded Greek ideas into the eastern world. A variety of religious movements—Christianity, Zoroastrianism, Manicheism—spread across that world. Many, if not most, of these movements were supported to a greater or lesser degree by Greek philosophical ideas. All three were underpinned by sacred books and thus induced a certain literacy. The major language was Syriac, which was itself a dialect of Aramaic. Many translations were made in the fifth century CE from Greek into Syriac. The major translation centers at this time were in Mesopotamia and the western borders of what is now Iran.

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The Islamic Ascendancy Then, late in the sixth century CE, a momentous event occurred. The Arabian peninsula had long been inhospitable to human settlement. Its burning sands had deterred the armies of the Mediterranean lands and it had been little influenced by the great civilizations of antiquity. Only a few permanent settlements had developed among its largely nomadic people. One of these, an ancient pilgrimage site some 70 km from the Red Sea, Mecca, saw the birth in 570 CE of one who was to change world history—the Prophet, Muhammed.

Islam Ascendant This is not the place, nor is there any need, to review the life and teachings of Muhammed. His message was compiled into the Muslim holy book, the Koran, shortly after his death in 632. In addition to the Koran the core Muslim literature contains many sayings attributed to the Prophet or to his followers and immediate successors, and these sayings are collectively known as Hadith. Muhammed’s message was so compelling that even before his death his followers (p.60) had overrun the Arabian peninsula and had begun to make incursions northwards. Very soon after his death the hugely energized adherents of the new religion had conquered the whole of North Africa and the Middle East. In 636 the Byzantine army was defeated in Jordan. In 638, in a victory of great symbolic importance, Jerusalem fell, and by 640 most of Syria was under Muslim control. Egypt followed and the Persians were defeated in Iran at the battle of Qadisiyyah. Finally, in 711, a small force from North Africa landed at Gibraltar, and after a decisive victory over the Visigoths at the Guadelete River, the whole of the Iberian peninsula fell under Muslim control. Not content with conquering Iberia, known to the Muslims as al-Andalus, the Muhammedan army crossed the Pyrenees into France and were only stopped and turned back by Charles Martel at the battle of Tours (or Poitiers) in 732. The Muslim conquerors did not require all their subject people to convert to Islam, although non-Muslims were not allowed to stand for the highest offices in government. Soon great centers of power and culture developed throughout the Muslim world. The Umayyads moved the Caliphate from Mecca to Damascus after the decisive split between the Sunni and the Shia Muslims in 661; in 750 the second Abbasid caliph, al-Mansur, abandoned Damascus and set up a new capital nearer the Muslim heartland, which became the splendid city of Baghdad. An alternative center of power was developed at Cairo by Shia Muslims under the Fatimid caliphs from the early 10th century. Finally, some of the most glorious and magnificent centers of Muslim power and culture were developed in Islam’s last conquest, al-Andalus, at Cordoba, Toledo, and Granada. The full extent of the Muslim empire and its major cultural centers at the close of the first millennium CE is shown in Figure 4.1.

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The Islamic Ascendancy Governing such vast territories led to many important consequences, one of which was that it soon became apparent that a common language was necessary. Unsurprisingly, in 690, the caliph Sulayman bin Abd al-Malik (c. 674–717) ruled that this should be Arabic. Thus every bureaucrat, everyone working for the Caliphate, everyone wishing to rise in society, had to speak and, even more importantly, write Arabic. Just as in medieval Europe Latin was the indispensable lingua franca, and in our times, at least for science and popular culture, English plays this role, so, throughout the vast tract of the Muslim world, from al-Andalus in the West to Afghanistan in the East, Arabic was the language used by the educated and the elite. This, as we shall see in the next section, had vastly important consequences.

Translation If Arabic were to be the language used throughout the Muslim world, it immediately became important that Arabic readers should be able to access the vast repositories of knowledge left behind after the decay of classical civilization. The great works of the ancients had, of course, already been widely copied and translated into the languages of the Levant—principally Syriac. In particular Jundishapur, in present-day Iran at the head of the Persian Gulf, had for over 500 years been a center where state-sponsored translation occurred. To translate, it has been said, is to traduce. It might be better to say that to translate is to transform. Montgomery, in his valuable book on the translation of science, shows how the writings of Aristotle, from the first probably an assemblage of notes taken by his students over a period of years, passed through a whole series of editors and copyists, often being adapted to different cultural settings or pedagogical practices, for several centuries after his death.1 If this happened to the greatest of the philosophers of antiquity we must assume that it also happened to a greater or lesser extent for other, less important, writers. If Jundishapur was the first great center of translation, predating the emergence of Islam by almost half a millennium, it was not long before the focus moved westwards to Baghdad. The first Abbasid caliph, al-Mansūr (714–775), started the process, but it only became highly organized under his grandson, Hārūn alRashīd (c. 766–c. 809). al-Rashīd sent emissaries to centers of scholarship and, in particular, Byzantium, in search of manuscripts. The translation of ancient manuscripts became yet more highly developed under al-Rashīd’s son, alMa’mūn (786–833), who during his caliphate (813–833) founded a research center, the Bayt al-Hikma or House of Wisdom, with the specific aim of translating the ancient wisdom into Arabic.

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The Islamic Ascendancy al-Ma’mūn’s House of Wisdom was directed by one of the great scholars of the age, Hunayn ibn Ishāq. Hunayn (808–873) was a Nestorian Christian,2 was bilingual in Arabic and Syriac, and had been trained in medicine by ibn Māsawaih. As a youth he had visited “the land of the Greeks” and had achieved a thorough knowledge of their language. Hunayn was assisted in his labors by his son, Ishāq, by his nephew, Hubaysh, and many others. It was a collaborative endeavor. It is, moreover, important to recognize that the translations (p.61) were, in general, not word-for-word transliterations, partly because Arabic words did not exist for many of the concepts found in the ancient originals. In many cases new words were formed, or the Greek or other ancient words merely adapted into Arabic. But, especially in the House of Wisdom, under the direction of Hunayn, translators sought to grasp the meaning of an entire Greek or Syriac sentence and reformulate it in Arabic.

This brings out an important point. The linguist and critic George Steiner emphasizes that, as we have already noted, translation necessarily involves transformation: “a message from a source-language passes into a receptor-language via a

Figure 4.1: Map of the Islamic world in the 12th century CE showing the major cultural centers. A = Alexandria; Ba = Baghdad; Bu = Bukhara; By = Byzantium (Constantinople); Ca = Cairo; Co = Cordoba; D = Damascus; F = Fez; G = Granada; I = Isfahan; Je = Jerusalem; Ju = Jundishapur; M = Mecca; Me = Medina; N = Nishapur; Sa = Samarkand;

Se = Seville; Ta = Tashkent; To = Toledo. transformational process.”3 He also emphasizes that this applies not only to translation from one language to another but also from one historical period to another of the same language. In our tracing of the historical development of the animal spirit doctrine this must always be borne in mind. Sabra, in his valuable article on the transformation of Greek science into that of medieval Islam, makes the same point: What the Muslims of the eighth and ninth centuries did was to seek out, take hold of and finally make their own a legacy which appeared to them laden with a variety of practical and spiritual benefits. And in so doing they succeeded in initiating a new scientific tradition in a new language which was to dominate the intellectual culture of a large part of the world for a long period of time. Translation is, at best, a pale description of an enormously creative act.4 Page 5 of 25

The Islamic Ascendancy The translation of ancient documents continued at a high level for more than a century after Hunayn initiated the enterprise in the House of Wisdom in the late ninth century. By the year 1000 almost the whole of Greek medicine, which remained documented in the great libraries of the Levant and the Byzantine Empire, as well the other sciences and mathematics, had been translated into Arabic. This, moreover, was not motivated by mere antiquarian interest. Arabic science in the medieval period was far from being a mere preservation of that which had been developed in more ancient times. The documentation retrieved from centers all over the Middle East was interpreted and reinterpreted to fit the different cultural and spiritual contexts of time; excerpts and commentaries were written and endlessly discussed. Figure 4.2 shows a palimpsest of scribal hands working and reworking a page of Avicenna’s book of healing.

Figure 4.2: Opening page of an Arabic commentary on Avicenna’s book of healing. It shows how manuscripts could be altered and overwritten by many different scribal hands. Translation from one language/one culture to another is seldom a fixed one-to-one operation but more often a generational transformative process involving many different minds and understandings. (From Montgomery, 2000, courtesy of Wellcome Library, London)

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The Islamic Ascendancy These translations, commentaries and commentaries upon commentaries formed the springboard from which the great efflorescence of medieval Islamic science sprang. In the 12th century, in the Latin west, Bernard of Chartres’ student and younger colleague, John of Salisbury (c. 1120–1180), recalled how his master insisted that we are “mere dwarves carried on the shoulders of giants, so that we can see more than they, and things at a greater distance, not by virtue of any sharpness of sight on our part, or any physical distinction, but because we are carried high and raised up by their giant size.”5 The same sentiment informed the careful long-continued translation work at al-Ma’mūn’s House of Wisdom.

Islamic Science In addition to founding the great translation center known as the House of Wisdom, Abdallah al-Ma’mūn was a strong supporter of the rationalist strand in Muslim thought against the dogmatisms of religious faith. A famous story tells of how al-Ma’mūn was visited in a dream by Aristotle, who advised him to seek God’s truth by opening his mind to the power of reason rather than wait to be instructed by revelation.6 Another story tells of how on gaining a victory over the Byzantines he asked for reparation not in gold and jewels but with a copy of Ptolemy’s Almagest. The House of (p.62) Wisdom was thus not only a translation center but also a research center. It seeded the growth of nearly 500 years of science and philosophy. Some of the key achievements of this efflorescence, while the West struggled through what are now termed the “Dark Ages,” are shown in Table 4.1. Table 4.1 necessarily omits many of the advances made in the 500 years of the Islamic ascendancy, from the foundation of Baghdad in 762 to its sack by the Mongols in 1258—a period of time greater than that which separates us from the publication of Copernicus’ De revolutionibus and Vesalius’ De fabrica in 1543. It should be noted, of course, that not all of the great advances listed in the table were achieved in Baghdad or its House of Wisdom. Many were made in the other great centers of the medieval Muslim world. Table 4.1 focuses on medical developments. It also lists salient advances in astronomy and engineering. Astronomy was, of course, of particular interest to the peoples exposed to the star-studded nights of the Middle East. It was also of great importance to the religious observances of Islam. Most mosques had their resident astronomer. Its study was also not distinguished from what we now know as astrology. The greatness of Islamic astronomy is recorded in many of the star names we use today and in the names of lunar craters. It also plausibly influenced the development of the heliocentric astronomy with which Copernicus broke the mold of European thought in the 16th century. The historian of science Otto Neugeberger noticed a similarity between Copernicus’ early study, the Commentariolus (1514), and

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The Islamic Ascendancy

Table 4.1: Islamic Chronology Science and Technology

Cultural Context 570 Birth of the Prophet Muhammed 622 Migration from Mecca to Medina (year 1 of Muslim calendar) 632 Death of the Prophet 634 Completion of the Koran 638 Conquest of Jerusalem 661–750 Umayyad caliphs rule in Damascus c. 690 Caliph Abd al-Malik decrees that Arabic should be used in all government documents 711 Expansion of Islam into Spain 732 Battle of Tours (or Poitiers) 762 al-Mansūr founds Baghdad

c. 763 First hospital opened in Baghdad c. 780 Jābir ibn Hayyān, “the father of chemistry” c. 800 Birth of al-Kindi, chemist and physician 813–833 Bait al-Hikma (House of Wisdom) developed by Caliph AlMa’mūn and directed by ibn Ishāq c. 820 al-Khwārizmī invents algebra c. 830 Banū Mūsā brothers invent many water-powered marvels and record them in the Kitāb al-Hiyal (Book of Artifices) c. 850 Hunayn ibn Ishāq (Johannitius) translates Galen’s Art of Medicine c. 850 al-Khwārizimi invents quadrant

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756–929 Umayyads rule in Spain

The Islamic Ascendancy

Science and Technology

Cultural Context

c. 850 Establishment of madrasahs (the first universities?) c. 870 Hunayn ibn Ishāq (Johannitius) publishes Ten Treatises of the Eye c. 852 ibn Firnas (Amen Firman) pioneers a hang glider c. 880 al-Dinawari founds Arabic botany with The Book of Plants c. 900 al-Rāzi (Rhazes): Kitāb al-shukuk ‘alā Jālinūs…(Doubts about Galen) c. 900 al-Rāzi (Rhazes): Kitab al-kabir (Great Medical Compendium) c. 900 al-Batani (Albategni) invents “the observation tube” and compiles astronomical tables c. 964 al-Rahman al-Sufi (Azophi) publishes star catalog 901–1000 Fatimids rule in Egypt 945–1045 Buyids rule in Baghdad c. 980 al-Majusi (Haly Abbas) publishes Kitab al-Maliki (Complete Book of the Medical Art) c. 996 al-Birūnī invents mechanical astrolabe c. 1000 al-Zahrawi (Albucasis) publishes a 30-volume medical encylopedia, the Al Tasrif c. 1000 Weight-driven mechanical clock and other mechanical devices invented c. 1020 ibn Sina (Avicenna) at work on alchemy c. 1027 al-Haytham (Alhazen) completes the Kitāb al Manāzdir (Optics) and publishes widely in mathematics, physics, and philosophy

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The Islamic Ascendancy

Science and Technology

Cultural Context

c. 1025 ibn Sina (Avicenna) publishes a 14-volume encyclopedia al-Qânûn fī’ltibb (The Canon of Medicine) c. 1027 Avicenna publishes a scientific encyclopedia c. 1030 al-Birūnī publishes astronomical encyclopedia, the Canon Mas’udicus, using a geocentric hypothesis 1037–1307 Seljuq empire c. 1077–98 Constantinus Africanus at Monte Casino publishes Latin versions of numerous Islamic texts, including Haly Abbas’ as the Pantegni c. 1090 Omar Khayyám publishes on mathematics 1116 al-Khazini publishes the Sinjaric astronomical tables giving the position of 46 stars in that year ? 1125 al-Ghazali publishes The Incoherence of the Philosophers c. 1150 al-Idrisi constructs world map and terrestrial globe ? 1150 ibn Rushd (Averroes) publishes The Incoherence of the Incoherence c. 1150 al-Baghdaadi critiques Aristotelian physics in his Kitab al Mu’tabar c. 1180 Gerard of Cremona translates Avicenna’s Canon into Latin 1206 al-Jazari publishes The Book of Knowledge of Ingenious Mechanical Devices describing some 50 mechanisms 1242 al-Nafis publishes critique of Avicenna’s Canon 1258 Sack of Baghdad by Mongols Page 10 of 25

The Islamic Ascendancy

Science and Technology

Cultural Context

c. 1263 Albertus Magnus publishes De animalibus 1230–88 al-Nafis publishes the first 80 volumes of a projected 300-volume Comprehensive Book on Medicine 1232–1492 Nasrid rule in Granada 1260 al-Tusi publishes Tadhkira, a critique of Ptolemy’s Almagest 1350 al-Shātir revises Ptolemaic astronomy 1453 Ottomans under Mehmed II capture Constantinople 1492 Muhammad XII expelled from Spain (p.63) al-Shātir’s account of the Moon’s motion. Investigating this intriguing similarity further, he found that one of Copernicus’ figures in the Commentarius matched one in al-Tusi’s Tadhkira, even to the extent of copying an apparent mistake in the lettering in al-Tusi’s illustration.7

Similar influences can be traced between other areas of Muslim thought and the European Renaissance. We shall consider these in more detail in the next section of this chapter. It is, however, worth noting here the line of influence stretching from Muslim hydraulic engineering to Descartes’ 17th-century neurophysiology. We shall see in Chapter 6 that a major inspiration of that neurophysiology took the form of visits to the Royal Gardens at St. Germain-en-Laye, where the young philosopher was greatly impressed by the water-driven statues the Francini brothers had installed in underground grottoes. The construction and enjoyment of water-driven automata may plausibly be said to have originated with the Banū Mūsā brothers in Baghdad’s House of Wisdom in the ninth century.8 The brothers published a volume detailing over 100 ingenious devices, translated as (p.64)

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The Islamic Ascendancy The Book of Artifices, in 830. It contained details of all manner of fountains and water-powered toys, including flutes that appeared to play by themselves and even a mechanical servant that poured the tea (Fig. 4.3). This and similar work led to numerous commentaries and translations, and the gardens of 15th- and 16thcentury Italian nobles were, in consequence, frequently enhanced by intricate fountains and waterpowered automata.9 It is thus no coincidence that the Francini brothers were 16th-century Florentine hydraulics engineers who, before Henri IV of France invited them to St. Germain-enLaye, had worked for Francesco de Medici, the Grand Duke of Tuscany, in his gardens at the Villa Pratolino. Returning, however, to the Islamic world, we cannot end Figure 4.3: (A) Elephant clock (Al-Jazari). without reference to the famous (B) Reciprocating pump for raising water, elephant clock that al-Jazari driven by animal or water power (Alconstructed at the beginning of Jazari). (C) Mechanical device for raising the thirteenth century (Fig. 4.3A). water (Al-Jazari). This famous elephant-shaped artifact was also water-powered and employed the striking of a cymbal and the chirping of a bird to mark the passage of time. The mechanism involved sophisticated devices such as flow regulators and closed-loop feedback mechanisms.

Another of the ingenious devices recorded in the Musa brothers’ book is a trick jug that used an intricate system of (p.65) internal tubes to control the flow of water or wine. This cannot but remind a modern reader of the intricate hydrodynamics of the vascular system. There is, however, no suggestion that the fascination of the medieval Islamic technologists with water in the ninth century led them to speculate about the cardiovascular system. Such speculation came much later, when al-Nafis, in the 13th century, undertook postmortem autopsies, and his dissections are said to have revealed the pulmonary and coronary circulation.10

Islamic Medicine

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The Islamic Ascendancy One of the Hadiths reports Muhammad as saying that “the best gift from Allah is good health” and another exhorts the faithful to “make use of medical treatment, for Allah has not made a disease without appointing a remedy for it, with the exception of one disease—old age.” Medicine was thus highly regarded in medieval Islam and many volumes and treatises were devoted to it. Although translations of Dioscorides’ first century CE Materia Medica formed the basis of Islamic pharmacy, translations of Galen formed the bedrock of Islamic medicine. The curriculum that medical students followed in medieval Islam appears to have been closely modeled on that constructed in late-classical Alexandria.11 Both Hunayn ibn Ishāq, known in medieval Europe as Johannitius, and, later, ibn Ridwān al-Misrī (d. 1061) give detailed accounts. The education appears to have focused on three major authorities: Galen (15/16 books), Hippocrates (4 books), and Aristotle (2/3 books). It also accepted Galen’s advice, who, as noted in Chapter 2, maintained in the title of one of his books that “the best physician must also be a philosopher.” Thus the thoroughly educated physician during the Islamic ascendancy had also studied logic, mathematics, physics, and metaphysics. As the Arabic translations of Galen and the other prescribed authors were always expensive, summaries and commentaries abounded. Because of an initial embargo on, or at the least discouragement of, human dissection (disregarded later, as noted above), much medical training was entirely theoretical, consisting in the mastery of the “set books” and commentaries.12 Galen’s book On Anatomical Procedures, although translated by Hunayn, is not in the early curriculum. In many cases students seem to have merely learned to recite the texts without having to show any understanding of their content. In other cases physicians seem to have been largely self-taught. This appears to have been the case with arguably the greatest of all Islamic physicians, ibn Sina (Avicenna).13 It is important also to note that, as in other areas of Islamic science, the translations from Greco-Roman originals were not always accepted uncritically. al-Rāzi (Rhazes), for instance, published quite early, at the beginning of the 10th century, an influential text challenging Galen: “It grieves me to oppose and criticize the man, Galen, from whose sea of knowledge I have drawn so much…Although this reverence and appreciation will and should not prevent me from doubting, as I did, what is erroneous in his theories.”14 Despite this growth of a healthy skepticism, Galen and, to a lesser extent, Aristotle remained the major theoretical forces behind medieval Islamic medicine, and it is to that medicine’s teaching about the nerves and animal spirit that we turn in the next section of this chapter.

Animal Spirit in Islamic Medicine

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The Islamic Ascendancy In this section we shall focus on the Islamic “neurophysiology” that most influenced subsequent European thought. This influence was due to the translation into Latin during the 11th and 12th centuries of Arabic medical compendia. Three of these compendia were particularly influential: Hunayn ibn Ishāq’s Art of Medicine (c. 850), al-Majusi’s Complete Book of Medical Art (c. 980), and ibn Sina’s Canon of Medicine (c. 1025). Hunayn (809–873) was known in the West as Johannitius, al-Majusi as Haly Abbas (d. 994), and ibn Sina as Avicenna (980–1037). In addition to these three great compendia, al-Haytham (Alhazen)’s Optics, published in about 1025, was highly influential in the early history of ophthalmology and physiological optics. Hunayn ibn Ishāq (Johaninitius)’s treatises were the first Islamic treatises to be translated into Latin. It was through these works that medieval scholars first became acquainted with Galen’s medicine. In the late 11th century Constantine the African (c. 1020–1098), with the help of his younger colleague Joannes Afflicius, translated among many other Islamic works both Hunayn’s Art of Medicine and Haly Abbas’s Complete Book of the Medical Art.15 Hunayn, as noted above, became known in the West as Johannitius, and Constantine’s Latin translation of the Art of Medicine came to be known as the Tegni.16 The Tegni was widely used as the basis of the medical curriculum being established in medieval European medical schools, in particular at the earliest of them all, that at Salerno in Italy. What did Hunayn have to say about physiology and animal spirit? He follows the account found in Galen, although not entirely uncritically. He believed, like Galen and the Alexandrian school, that the optic nerve was hollow. He was, however, more skeptical about the tubular nature of the other nerves. Indeed, he writes that such cannot be true of “very fine nerves” as their walls would not be strong enough to contain animal spirit.17 He follows Galen and other anatomists of classical antiquity in classifying sensory nerves as “soft” and motor nerves as “hard.” This accords with his theory that animal spirit in the sensory nerves, in (p.66)

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The Islamic Ascendancy particular the hollow optic nerve, carries imprints of sensations to the brain. The “hard” motor nerves, however, carry force, resembling a percussive force, via the animal spirit within.

Hunayn’s Ten Treatises on the Structures of the Eye is recognized as the earliest existing systematic textbook of ophthalmology and includes the earliest known figure of the eye (Fig. 4.4). After a comprehensive account of the eye and its muscles, seemingly derived from first-hand dissection, Hunayn outlines his theory of how vision occurs. First, however, he provides an account, largely from Galen’s De usu partium, of the brain and its function.

Figure 4.4: Hunayn’s anatomy of the eye. (From Meyerhof, 1928)

The brain, he writes, is the source of perception, voluntary movement and the will. It contains four cavities (ventricles): two anterior, one middle, and one posterior. Vital spirit arising from the heart is carried by two arteries (our carotids) to the brain and it is there refined to form animal spirit, which is secreted into the two anterior ventricles, where it remains while it is further refined. Coarse particles are removed via the nostrils and mouth. The refined animal spirit then passes into the middle ventricle (our second ventricle) for further refinement and finally into the posterior ventricle. The passage from the middle to the posterior ventricle is, Hunayn writes in one of the most interesting passages, via a narrow canal (our iter or aqueduct of Sylvius), but this passage can be blocked by “something resembling a worm.”18 The canal, he explains, is blocked until “Nature intends to admit animal spirit from the middle to the posterior cavity.”19 The posterior ventricle, he continues, is responsible for movement (presumably voluntary movement) and for recollection: in other words, for conscious activity. The spirit in the anterior ventricles is concerned with perception and imagination while that in the middle ventricle is occupied with “reflection.”

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The Islamic Ascendancy There are, writes Hunayn, two possible ways in which animal spirit can cause perception and movement. Either its power enters the nerves, much as the sun illuminates the air, without its substance moving,20 or the spirit itself enters the nerves. There are two possibilities here also: either the spirit “runs along the nerve until it reaches the sensitive or moveable organ” or it flows into the nerve a certain distance so that the latter’s substance is altered, and this then continues along the nerve to the appropriate organs.21 It can be seen that Hunayn’s theory prefigures, in principle, modern ideas of neuromuscular physiology. An influence from the brain does, indeed, travel out from the brain to the muscles and initiate movement. It is, however, more difficult for moderns to understand his neurosensory physiology, for Hunayn wants this centrifugal spirit to do the same thing for perception. The most difficult case is provided by the visual sense. How can an outwardly flowing animal spirit account for vision? To explain how it is that we see distant objects, Hunayn makes use of a version of visual physiology that can be recognized as Platonic in origin.22 Animal spirit refined in the anterior ventricle flows down the optic nerves to the eyes and is concentrated in what he calls “the ice-like humor” (the lens).23 Then, in a discussion that moderns find difficult to accept, he argues that the visual spirit in the lens alters the surrounding air so that it “extends itself” until it reaches the object of vision. He makes the analogy of a blind man feeling objects with a stick. Vision is like that. A column of altered air, a searchlight beam, searches the visual space. When the visual spirit (which must necessarily flow from the brain in large volumes) emerging from the lens “meets the surrounding air, it strikes it as it were with a shock of a collision, transforms it and renders it similar to itself.”24 This account of sensory physiology is clearly very different from that which we nowadays accept. For Hunayn and his students, animal spirit, in its sensory capacity, runs out to the extremities of the body, or even, as in the case of vision, to the extremities of sight, to “feel” the sensory object. (p.67) The fundamental sense, as with Aristotle, is that of touch. The spirit feels the sensory object and reports back to the appropriate region of the brain: “the contact is perceived where it occurs,” he writes, “but only when the perception reaches…the brain… and is perceived by the allotted part of the soul” is the process complete and the distant object consciously recognized.25 This Platonic extromission theory of vision, common in the early years of the Islamic ascendancy, was controverted and put to rest by the brilliant researches of al-Haytham (964–c. 1040). These researches were published around 1027 in his Kitāb al Manāzdir (Optics). He established that sight was not due to any projection from the eye but to the reception of an influence from the outside world.26Alhazen’s Optics, in its late-12th-century Latin translation (De aspectibus), became, as Russell remarks, “the most influential text on visual optics in the West.”27 Page 16 of 25

The Islamic Ascendancy The second highly influential medical writer considered in this section, al-Majusi (Haly Abbas), published his Complete Book of the Medical Art at the end of the 10th century and it, too, was translated by Constantine Africanus.28 He gave it the Latin title Pantegni, the Complete Art.29 The translation is also sometimes known as Liber Regius or Royal Book (Fig. 4.5). It is sometimes regarded as the first comprehensive medical text in Latin.30 Haly Abbas’ compendium is almost completely Galenical in character. The brain, he writes, is the most important organ of the body because it is here that the power of the rational soul is manifest. It contains anterior, middle, and posterior cavities: the ventricles. The anterior ventricle is, in fact, a double cavity (our lateral ventricles). He followed Galen in writing that the carotid arteries carrying vital spirit (spiritus vitalis) from the heart deliver that spirit to a rete or net-like complex at the base of the brain where it is secreted into the substance of the brain. It percolates through the cerebral substance to be eventually released into the anterior ventricles in a highly filtered and refined form as animal spirit (spiritus animalis). From the anterior ventricle it passes back to the middle and posterior ventricles. Once again the passage from the anterior to the posterior ventricles is controlled by a worm-like body or vermis, which acts as a valve. The animal spirit in the anterior ventricles is involved with sensation and imagination, that in the middle ventricle with intellect or reason, and that in the posterior ventricle with motion and memory. We can recognize in this account the same ideas that Hunayn was propagating in his Art of Medicine and Ten Treatises a century or so earlier. In both cases the major source is, of course, Galen’s work in the second century and, in particular, his text De usu partium corporis (On the Usefulness of the Parts of the Body). It is also important to note that in both cases animal spirit is not the rational soul itself, but its instrument. Furthermore, as in Galen’s work, the cranial and spinal nerves were divided into hard and soft types.

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The Islamic Ascendancy The soft nerves were, in general, sensory while the hard nerves were motor.

The third highly influential, indeed the most influential of all, Islamic medical writing was that published some 50 years after Haly Abbas’ Book of Medical Art: ibn Sina (Avicenna)’s 14-volume alQânûn fī’l-tibb (Canon of Medicine) (Fig. 4.6). Avicenna’s interests extended far beyond medicine and its practice. Like many of the great Islamic thinkers he was every inch a polymath. He published important works on theology and metaphysics, on physics and history, as well as on medicine.31 But it is his work on medicine and his neurophysiological ideas that Figure 4.5: Haly Abbas: Liber totius concern us in this section. The medicinae (The Complete Book of al-Qânûn fī’l-tibb was translated Medical Art), J. Myt, Lyons, 1523. into Latin by Gerard of (Courtesy of Wellcome Library, London) Cremona (c. 1114–1187) as the Liber Canonis Medicinae (Fig. 4.6). It differs from the compendia published by Hunayn and Haly Abbas in showing a strong Aristotelian influence in addition to that of Galen. In particular, and importantly, Avicenna argues that the heart, (p.68)

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The Islamic Ascendancy not the brain, is the physiological center of sensation and voluntary motion.

Figure 4.6: Avicenna: Canon of Medicine, title page. Rome, 1593. (Courtesy of Wellcome Library)

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The Islamic Ascendancy He follows Galen and his Islamic predecessors in accepting that the animal spirit in the brain is confined in three chambers, the first concerned with the sensus communis (common sensorium, often confusingly labeled “common sense”) and imagination, the second with cogitation and reason, and the last (most posterior) with memory.32 He also accepts that the nerves controlling bodily movement and involved in sensation take their origin from the brain and spinal cord. Like all his predecessors he only recognized seven (not twelve) pairs of cranial nerves. For these early anatomists the vagus nerve (our tenth) was a branch of the sixth, and Avicenna gives it a careful description. It is not for nothing that it obtains its name from the Latin for “wanderer” or “vagrant”: it has many convolutions and branches. The cardiac branch was destined to play an important role in Avicenna’s neuropsychology. Figure 4.7, from the Canon of Medicine, shows Avicenna’s sketchy understanding of the rest of the nervous system.

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Figure 4.7: Avicenna: Canon of Medicine, nervous system. (Courtesy of Wellcome Library, London.) See also the very similar figure in the medieval “five-figure series” (Fig. 5.6).

The Islamic Ascendancy Avicenna seeks to reconcile Galenic and Aristotelian neuropsychological ideas by arguing that the heart is the center or “ultimate root” of all the powers of the body, including those by which it perceives and undertakes voluntary movement.33 He points out that this is the opinion of the “Philosopher” (Aristotle) who, he writes, proved this to be the case with arguments of great subtlety and rigor. (p.69) The brain, in contrast, is no more than a servant of the heart. The impulse for voluntary movement, for instance, starts in the heart and is transmitted to the brain, which then sends out animal spirit down appropriate nerves to the body’s musculature. The transmission between the heart and the brain is made via the cardiac branch of the vagus nerve. Similarly, when sensory nerves deliver messages from the periphery to the brain, these messages are transmitted, should they need attention, via the vagus nerve to the heart. Thus Avicenna brings together his philosophical learning and his medical knowledge. He is careful, however, in this passage in the Canon to assure physicians that they can carry out their art perfectly well without puzzling over this unification of cardiocentric and cerebrocentric neurophysiologies. As physicians, he writes, it is perfectly acceptable to continue with the time-honored Galenic cerebrocentric scheme.34

Concluding Remarks This very rapid résumé of the 500 years when the cutting-edge of science and medicine shifted from the Latin West to the Islamic East has shown how the great medical synthesis associated with the name of Claudius Galen was taken over and slowly developed. This development was partly by renewed anatomical investigation, although dissection was frowned upon and not frequently practiced, and partly by theoretical argument. We have just seen how Avicenna, perhaps the greatest of Islamic physicians, sought to combine his knowledge of Aristotelian metaphysical theory with his understanding of Galen’s biomedicine. This concern with theory surfaces throughout medieval Islam, especially in the most highly trained and educated physicians. They took very seriously Galen’s advice that “the best physician should also be a philosopher.”

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The Islamic Ascendancy It has been argued that not only philosophical speculation but also the very practical interests of the engineer, in particular the hydraulic engineer, influenced medieval Islamic neurophysiology. Fascination with water and the devices it could be made to power is not surprising in the sun-drenched lands of the Middle East, where irrigation and water management are essential for civilized life. We noted how the Book of Artifices published by the Banū Mūsā brothers in c. 830 described large numbers of water-powered artifacts. The cerebrocentric neurophysiology taught by the majority of Islamic physicians marches well with this interest in hydraulic engineering. The cerebral ventricles act as reservoirs of a “fluid” animal spirit, which exerts its effects either by flowing down the nerve fibers or by pressure changes in a column of spirit within the nerves. This, of course, is not an entirely new concept with the Muslim physicians: tripartite ventricular neurophysiology is to be found in St. Augustine and Nemesius at the close of classical civilization in the Latin West.35 It seems to have been taken over by Islamic scholars along with so much other classical learning. Finally, as we shall see in Chapter 5, late in the 11th century and on into the 12th century, the Arabic writings began to be translated into Latin. The most important early translator was, as we noted, a Muslim native of Tunisia, Constantine the African, who, driven out of his native land, arrived in Salerno laden with Arabic texts in 1077.36 The translation activity initiated by Constantine, who converted to Christianity and took on religious orders at the great Benedictine monastery at Monte Casino, was soon taken up by others and formed the background syllabus, the Articella, of the medical school at Salerno. The Salernitan Articella soon spread to other early European medical schools and was supplemented by translations of Avicenna’s Canon.37 Foci of Arabic-toLatin translation developed in several other centers of the Latin West, especially in Cordoba and Toledo. Islamic medicine, and within it neurophysiology, continued its development after the great works of the 10th and 11th centuries. In the middle of the 13th century al-Nafis began work on a great 300-volume Comprehensive Book on Medicine but died before he could publish more than the first 80. But from the point of view of the history related in our book, the growth points in scientific medicine and neurophysiology had by this time shifted back to Europe. In 1258 Baghdad and its great library resources were destroyed by the Mongols, and in 1492 the Muslims were forced to withdraw from their last stronghold in Europe, the Spanish city of Granada with its red fort, the Alhambra. The last Sultan, Muhammad XII, known to the West as Boabdil, is said to have looked back in tears at the Alhambra as he retreated to the coast, only to be upbraided by his mother: “What you could not hold as a man you should not regret as a woman.” (p.70) Notes: Page 22 of 25

The Islamic Ascendancy (1) Montgomery, 2000, pp. 6–10. (2) Nestorians believed that Christ had two loosely intertwined natures: human and divine. In contrast, Monophytists believed that he had but one nature, the human absorbed into the Divine. Nestorianism was condemned as heretical in 431 and 452, and its adherents consequently migrated eastwards and found refuge in centers such as Jundishapur. (3) Steiner, 1975, p. 28. (4) Sabra, 1987, pp. 225–226. (5) John of Salisbury, 1159, Metalogicon, 3, 4 (McGarry, 1955). (6) Lyons, 2009, Chapter 3. (7) Neugeberger, 1957. See also Masood, 2009, pp. 134–137. (8) Purists will argue that the line of influence should be traced back yet further, through the translators to Hero of Alexandria and others in Greco-Roman antiquity. (9) For discussion see Bedini, 1964; Adams, 1979. (10) Nagami, 2003. (11) Iskander, 1976, gives a valuable summary; see also Leiser, 1983. Medical education in Alexandria continued until the 720s CE. (12) An extensive account of the position of postmortem dissection during this period of Islamic culture may be found in Savage-Smith, 1995. Dissection of animals (including primates) seems, however, to have caused no particular disapprobation. In his Ten Treatises of the Eye (c. 850 CE) Hunayn describes how the brain should be dissected in order to see the origins of the optic nerves (Meyerhof, 1928, pp. 21–22). (13) Leiser, 1983, p. 51. (14) Quoted in Masood, 2009, p. 100. (15) See Frampton, 2008, Chapter 5. Constantine was a Tunisian Muslim driven from his homeland in 1077 first to Salerno and then, after converting to Christianity, settling in the great monastery of Monte Casino, where he set about translating into Latin the large number of Arabic books he had brought with him. (16) “Tegni” is the shortened version of the full Latin title: Isagoge Johannitii ad Tegni Galeni primus liber medicine. Page 23 of 25

The Islamic Ascendancy (17) Meyerhof, 1928, p. 30. (18) Ibid., p. 18. See also Chapter 2, where the source of Hunayn’s statement in Galen’s De usu partium is cited. It has been pointed out that it is, in fact, unlikely that Galen located the “worm” in the aqueduct of Sylvius but rather in spaces between the medulla and the overlying cerebellum (trans. May, 1968, p. 420). (19) Can we see here a misty forerunner of Descartes’ 17th-century pineal neuropsychology, which we shall describe in Chapter 6? (20) Again we feel Galen’s influence. We saw in Chapter 2 how Galen makes a similar comparison in De locis affectis. (21) Meyerhof, ibid., p.28. (22) We read in the Timaeus (45B–46A) of how “the pure fire that is within us… flows forth through the eyes in a stream smooth and dense. Consequently whenever there is daylight round about the visual current, this latter flows forth…and coalesces with it and forms into a single homogeneous body in direct line with the eyes wheresoever the current issuing forth from within collides with some external body. Thus the whole, because of its homogeneity, is likewise affected and transmits throughout the body to the soul the motions of anything it encounters or that encounters it and thereby produces the sensation we call ‘seeing’”. Plato’s Pythagorean theory was taken up by the Stoics and can be found in Nemesius’ early-fifth-century Nature of Man (Nemesius, p. 324). (23) Anyone who has dissected an ox eye will recognize Hunayn’s description of the lens. (24) Meyerhof, ibid., p. 37. (25) Ibid., p. 29. (26) See Russell, 1996. (27) Russell, 2010, p. 71. (28) For more detail on Haly Abbas see Fisher, 1883. (29) More precisely: Pantechni decem libri theorices and Pantechni decem practices. (30) Frampton, 2008, p. 334. (31) The great range and importance of Avicenna’s thought is brought out in the publications of the Yale University Avicenna Study Group conferences (2001, 2004).

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The Islamic Ascendancy (32) Detail of Avicenna’s ventricular neuropsychology may be found in Rahman, 1952. (33) Avicenna, Canon, I, 1: quoted in Frampton, 2008, p. 370. Avicenna, following Aristotle, makes a philosophical argument for the primacy of the heart in the Kitāb al Najāt, Book II, Chapter XV (see Rahman, 1952, p. 66). (34) Ibid., p. 370. Nevertheless, Avicenna’s hybrid views were taken up by significant figures in the medieval Latin West, including Albertus Magnus (see Chapter 5). (35) The three-ventricle (or three-cell) schematic first appears in the work of the fourth-century physician Posidonius and then (better known) in Nemesius’ De natura hominis (On the Nature of Man) and in St. Augustine of Hippo’s earlyfifth-century De genesi ad litteram libri duodecim (the Literal meaning of Genesis in Twelve Books). (36) See Frampton, 2008, p. 323. (37) Interested readers can find the complete contents of the Articella as studied in the early 16th century in Giunta, 1534.

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Animal Spirit in an Age of Faith

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Animal Spirit in an Age of Faith C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0005

Abstract and Keywords This chapter centers on the development of the animal spirit and Christian thought in relation to both the spirit and knowledge of the material world. It reveals that the enduring doctrine of the animal spirit only came under suspicion towards the end of the 16th and start of the 17th centuries. The discussion first studies the functional divisions of the brain. Here, it refers to the three cavities or ventricles where—based on the accepted medical theory at the time—pneuma was collected before being distributed to the body via the nerves. Next, it studies the impact of Aristotle and the Thomist synthesis, which blended Aristotelian philosophy with Christian doctrine. This chapter also discusses neuroanatomy during the Renaissance and some thinkers who felt the tensions between the newer and older ways of thinking. Keywords:   animal spirit, Christian thought, functional divisions, pneuma, Thomist synthesis, Renaissance, neuroanatomy

The brain, being the most important of the animal members…has also subservient members, namely, the nerves; for the animal spirits are carried by the nerves to all the members, endowing them with sensation, motion, and what not.…It has much of spirit and much of marrow.…It is divided into three cells, the cellula phantastica in the anterior part of the head, the cellula logistica in the middle, the cellula memorialis in the posterior part.

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Animal Spirit in an Age of Faith The Anatomy of Nicolai the Physician (12th century, trans. Corner, 1927, pp. 69–71) Who (in God’s immortal name I ask it!) can fail to marvel at the crowd of philosophers (and, I might add, theologians) of our time who so ludicrously demean that divine and most wonderful device, the human brain, on the basis of dreams of their own which show a startling lack of piety toward the founder of the human fabric? Vesalius, 1543, De humani corporis fabrica, Book VII, Chapter 1, p. 623 (trans. Richardson and Carman, 2002–2009, p. 163) We noted in Chapter 3 how theologians like Augustine of Hippo and Isidore of Seville became absorbed in definitions, etymologies, and the meanings of words. We saw how the notion of “spirit” acquired a transcendental Christian connotation and how it assumed the semantic ambiguities that it retains to this day—the human “spirit,” yet also the “spirits” that one finds being sold in public houses and bars. The men and women of those embattled times lived in a world built of a very different system of meanings from those with which we are familiar today. It was a world focused on the world to come, a world centered on ecclesiastical interpretation, a world full of symbols—mysterious, unfathomable, dangerous. Yet, as historian Lynn White has so eloquently shown in an article on technological progress during the Middle Ages, also a world in which a stop– start development of technology, of military hardware, and of labor-saving agricultural devices was also occurring.1 In this chapter we shall explore the evolution of our subject along both of these lines: Christian thought in relation to both spirit and knowledge of the material world, and in particular as regards the actual organization of the human body. It will be convenient to start with the functional divisions of the brain, with particular reference to the three cavities or ventricles where, according to accepted medical theory at the time, pneuma was collected for distribution to the body through the nerves.

“Cellular” Psychology

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Animal Spirit in an Age of Faith We have seen in previous chapters how the brain’s ventricles had intrigued philosophers and physicians since the Alexandrian anatomists of the fourth century BCE. In Chapter 2 we noted that Herophilus had concluded that the third (our fourth) ventricle was the likely seat of the soul. In the same chapter we noted that 500 year later, in the second century CE, Galen had come to much the same conclusion, regarding the third ventricle as the most important. Next, in Chapter 3, we reviewed how some 150 years later Posidonius of Byzantium had developed these ideas further, reporting that damage to the anterior region of the brain affects imagination, damage to the middle ventricle impairs reasoning, and damage to the posterior part is detrimental to memory.2 This was followed in that same chapter by an account of how finally at the end of the fourth century Nemesius, Bishop of Emesa, in his De natura hominis—a thoroughgoing treatise on the philosophical and theological understanding of humankind—assigned the faculties of sensation and imagination to the frontal cavities of the brain, (p.72) thought to the middle cavity, and memory to the posterior one. This attribution of psychological faculties (i.e., belonging to the psyche or soul) to the three major reservoirs of pneuma in human anatomy, being presented by an erudite member of the ecclesiastical hierarchy, was translated into several languages and became an accepted fact in Christian teaching. The Nemesian schematic remained standard theory for at least eight centuries, since a variant of it can be found in an Anathomia written by “Master Nicolai the Physician” in about 1200. Using the Latin term cellula, diminutive of cella—that is, a small room or space—to denominate each of the cerebral ventricles, he provides the following description of the general structure of the brain: “It is divided into three cells, the cellula phantastica in the anterior part of the head, the cellula logistica in the middle, the cellula memorialis in the posterior part.”3 Such functional differentiation between the three cerebral “cells” is related to their individual amount of heat and moisture, for “The first cell is hot and dry,… the second is hot and moist,…the third is cold and dry.” Of equal importance, Nicolai continues, is the relative proportion of spirit and marrow,4 since the role of spirit is “to provide sensation and motion in the members and to carry on the various activities of the mind,” whereas that of the marrow is “to permit the free perception of diverse forms and shapes.” Accordingly, the “cellula phantastica…has much of spirits, to provide for the carrying on of its functions, and it has little marrow, in order not to impede the flow of spirits in apprehending the nature of things.” Similarly, the second one, or “cellula logistica…has much of spirits, in order that there may be full discrimination of ideas received,” though also “it has much marrow, in order that the spirits depleted by these subtle operations may be replenished.” Finally, the “cellula memorialis…has much marrow, that it may be easily stamped with the impressions of diverse ideas, but not much spirits, which might flow about and remove the impressions of ideas.” These features led Nicolai to provide the following interpretation: Page 3 of 49

Animal Spirit in an Age of Faith On account of the three divisions of the brain the ancient philosophers called it the temple of the spirit, for the ancients had three chambers in their temples: first the vestibulum, then the consistorium and finally the apotheca. In the first, declarations were made in law cases, in the second, the statements were sifted, in the third the final sentence was laid down. The ancients said that the same process occurs in the temple of the spirit that is the brain. First, we gather ideas into the cellula phantastica, in the second cell we think them over, in the third we lay down our thought; that is, or commit to memory.5 We are also told “the brain has also subservient members, namely, the nerves; for the animal spirit is carried by the nerves to all the members, endowing them with sensation, motion, and what not.”6 These spirit-distributing connections are in turn linked to the cerebral “cells”; furthermore, “according to some authorities, all the sensory nerves originate from the cellula phantastica, the motor [ones] from the cellula memorialis.”7 The absence of genuine anatomical advance in the medieval period virtually ensured that ventricular psychology would quickly lose touch with neuroanatomical reality. Although Galen and his Islamic followers were fully aware that the anterior ventricle is, in fact, a paired structure, most medieval diagrams showed there to be not four but only three cavities. These, moreover, came to be represented as circles, most probably following the classical idea that the circle and the sphere are the most “perfect” geometrical figures, and therefore well suited for containing the animal spirit. Galen’s dissections had necessarily found the ventricles in a collapsed state, but even he, arguing for the many advantages of rounded shapes, stated that they were spherical cavities in life.8 The three rounded cavities became known simply as “cells” (cellae), in correspondence with the three main “internal senses” or “faculties of the mind” in the Nemesian model—thus imagination and fantasy would be associated with the anterior cell, rational thought with the middle one, and memory and reminiscence with the posterior cell (Fig. 5.1). Not all the medieval writers followed this three-cell schematic. Thus Avicenna (981–1037), in a non-Christian tradition, favored a quintuplet series.9 In this model the five

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Animal Spirit in an Age of Faith (p.73)

Figure 5.1: One of the earliest known representations of the cerebral ventricles or “cells” (cellae), illustrating the medieval “cell theory” of psychological faculties, from an 11th-century manuscript. The skull faces diagonally downwards and shows the coronal, sagittal, and lambdoid sutures. The three internal cavities are labeled (from front to back) “fantasia,” “intellectus,” and “memoria” (from Clarke and Dewhurst, 1972, p. 10).

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Animal Spirit in an Age of Faith senses deliver their inputs to the first cell (i.e., the common sensorium or sensus communis) and this is followed by four more cells in series devoted respectively to fantasia, imaginatio, cogitatio, and memoria (Fig. 5.2). Later Roger Bacon (1219–1292), a Franciscan friar, would present the five interconnecting cells envisioned by Avicenna, with much the same functions.

And there were many more variants. In an exhaustive paper on the ventricles,10 Manzoni lists over 60 different accounts of the medieval cell theory, ranging from the fourth to the sixteenth century, and from Byzantine, through Arabian and Hebrew, to Latin interpretations.

Figure 5.2: Medieval diagram showing a five-cell schematic from Avicenna’s De generatione embryonis copied in about 1347 (from Clarke and Dewhurst, 1972,

But we are getting ahead of our narrative. Let us retrace our p. 30). steps to the beginning of the 11th century. Simply copying, citing, and quoting “established” knowledge coming from a literally immemorial origin would not continue much longer. In the 11th century CE the Western Christian world was swayed at its foundations by the appearance of Latin translations from Arabic editions of the writings of Greek antiquity, and then by direct translations from the Greek itself.

Rediscovery of Antiquity At the conclusion of Chapter 4, we saw how the great era of Muslim ascendancy began to wane at the turn of the first millennium CE, and that by the end of the 15th century, in the same year that Columbus discovered what he believed to be a short passage to China, the last sultan was finally forced to retreat from mainland Europe. But well before 1492, the cutting edge of intellectual advance had shifted from Baghdad and the other intellectual centers of the Arabic Middle East to the formerly benighted lands of Western Europe. Complex forces were undoubtedly at work, but chief among these was the development of centers for the translation of important documents from Arabic and, later, from Greek, into Latin, in Sicily, southern Italy, and Spain.11

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Animal Spirit in an Age of Faith The earliest of these translations, as noted in Chapter 4, were from Arabic works brought by Constantine the African to Salerno (c. 1020–1087). The medical school at Salerno had become a renowned medical center by the late 10th century, and its faculty was intensely interested in acquiring the sophisticated knowledge enshrined in Arabic medical texts. Constantine Africanus arrived in Salerno from Tunisia in 1077, carrying many Arabic books.12 The Archbishop of Salerno at the time was the Benedictine monk Alfanus (c. 1015–1085). As a young man, Alfanus had traveled widely in the Eastern Mediterranean, living for a time in Constantinople, and was fluent in Greek. Together they ensured that the medical school was supplied with translations of medical treatises, both from the Arabic and from the original. This intensive translation activity, initiated by Alfanus and Constantine (who later converted to Christianity and entered the great Benedictine monastery at Monte Casino), was taken up by others and formed the syllabus, the Articella, of the medical school. Maurus of Salerno (c. 1130–1214) put together the earliest known version of the Articella at the end of the 12th century. It consisted of five or six short texts derived principally from Constantine’s translations from the Arabic.13 Versions of the Salernitan Articella soon spread to other European medical schools and were supplemented by further translations from the Arabic and Greek, especially Aristotle and Avicenna’s Canon of Medicine. This great translation activity at Salerno continued into the next century. The focus then shifted from southern Italy to Moorish Spain, where Toledo and Cordoba became the most important centers, although there were also translation hubs elsewhere in Southern Europe. Two important names stand out from this time: Gerard of Cremona (c. 1114–1187) and Willem or William of Moerbeke (c. 1215–1286). Gerard of Cremona spent most of his life in Toledo, where he translated a great number of Arabic works into Latin.14 Historian Charles Haskins writes that “more Arabic science in general passed into western Europe at the hands of Gerard of Cremona than in any other way…[and where they] have been tested, they have been found to be closely literal and reasonably accurate.”15 In addition to the usual physical and (p.74) philosophical texts, his translated works include 10 of Galen’s treatises, Rhazes’ Short Introduction to Medicine, and the whole of Avicenna’s Canon of Medicine. These books, as noted above, became an indispensable part of the medical curriculum. The great medical educationist William Osler (1849–1919) referred to the Canon as “the most famous medical textbook ever written,”16 for it was used in some Western medical schools until the middle of the 17th century.

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Animal Spirit in an Age of Faith The other important translator during the Middle Ages was Willem of Moerbeke. Like many of the other great intellects of the period, he was a Dominican monk. The Dominicans, founded by Dominic Guzman (1170–1221), were a teaching order devoted to expounding and explaining the Christian religion to the laity. Willem, although born in what is now Belgium, became Bishop of Corinth and thus well acquainted with the Greek language. He is best known for translating the works of Aristotle directly from Greek into Latin, as well as those of the third-century commentator on Aristotle, Alexander of Aphrodisias (fl. c. 200 CE), and the sixth-century Christian philosopher Joannes Philoponus (c. 490–570 CE). He was encouraged in these activities by his slightly younger and considerably more famous friend, Thomas Aquinas (1225–1274), who was destined to unify Aristotelian teaching with Christian dogma (see below). By the end of the 13th century most of the major surviving works of classical antiquity had been recovered and were available in Latin. This was a revelation. It is difficult to find a comparison, but it must have been similar to the shock that Asian civilizations, especially those of Japan and China, experienced when the scientific writings of the European West became more available to them during the 18th and 19th centuries.17

The Impact of Aristotle Although the greater part of Aristotle’s philosophy had been translated into Latin by the 12th century, it was not always popular with the Church’s authorities. In particular they disliked his view that the world had always existed, since this ran counter to the Church’s dogma that the Deity had created it in 7 days. Consequently, his teachings had a somewhat checkered history. They were condemned in 1210 when the Faculty of the University of Paris, Europe’s premier school of theology, was told by the ecclesiastical authorities that “Neither the books of Aristotle on natural philosophy, nor their commentaries, are to be read in Paris in public or in secret, and this we forbid under pain of excommunication.”18 Similar prohibitions were pronounced elsewhere during the later years of the 13th century. It seems, however, that these threats were more honored in the breach than the observance, and they were finally withdrawn altogether in 1325. Despite these doubts about Aristotle’s philosophy, two great 13th-century theologians ensured that Aristotle’s writings were studied: Albertus Magnus (Albert the Great, c. 1206–1280; Fig. 5.3A) and his junior colleague, Thomas Aquinas (1225–1274) (Fig. 5.3B). Their influences on the medieval intellectual world were immense.

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Animal Spirit in an Age of Faith Albertus was born at Lauingen in Swabia (southwest Germany) and received his university education in Padua, Italy. He was a great traveler and studied in many of the important intellectual institutions of medieval Europe, ultimately receiving his doctorate in theology at the most prestigious of them all, the University of Paris. It was there that he met and became friends with the 20-year-old Aquinas. Both were elected to the Dominican order of preachers. Despite constantly traveling throughout Western Europe, Albertus wrote on practically every subject, from logic and the physical sciences to psychology, politics, metaphysics, and, of course, theology and biblical exegesis.19 Most important for us here is that he became greatly interested on the whole of Aristotle’s extant writings, absorbing and interpreting them, even translating some of them into Latin, for use as a framework in his own philosophy, particularly natural philosophy. For Albertus was convinced that the material world, as the product of divine creation, was also worth studying in every detail. In addition to his insatiable book learning, Albertus possessed a rather empirical cast of mind for the time in which he lived. His frequently expressed motto was “Fui et vidi experiri” (“I have been [there] and seen it tested by experience”). When unable to see things with his own eyes, he turned to testimonies provided by witnesses he viewed as learned and reliable. With regard to the electric ray or torpedo fish, for example, he wrote in his De animalibus (Book XXIV) that “It numbs [stupefacit] anyone touching it, no matter how fast he might withdraw his hand. It does so with such power that one of our comrades, just poking at it with the tip of his finger, touched it and just barely regained sensation in his arm within half a year by means of warm baths and unguents.”20 Although Albertus’ books about nature contain many myths, as was common in the bestiaries of his day, he did much to draw fresh attention to the study of nature. His scholarly output was truly gigantic, and he fully deserved the title of Doctor Universalis bestowed on him by the Roman Church. Thomas was less interested than Albertus in natural philosophy but was destined to become a more influential theologian. It might be said that the pupil–master relationship was the reverse of that between Aristotle and Plato as depicted by the Renaissance artist Raphael (1483–1520) in his great painting, The School of Athens.21 Instead of the (p.75)

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Animal Spirit in an Age of Faith pupil—in this case Aquinas— pointing to earthly things, he would point heavenwards while his master, Albertus, would point down to things of this world.

When Albert left Paris for Cologne the young Aquinas accompanied his professor, and they both took up academic positions in that Rhineland city. This early and continuing connection between Albertus and Thomas is important, because through their friendship the latter came to recognize the relevance of Aristotle, and later on attempted a full integration of

Figure 5.3: (A) Albertus Magnus (c. 1206–1280) lecturing to students. (A 19th-century engraving) (B) Thomas Aquinas (1224–1274) by Fra Angelico. (Courtesy of the Wellcome Library, London)

Aristotelian philosophy and Christian theology. The result ensured that the intellectual threat posed to Christianity by the reappearance of classical Greek thought, as a consequence of the translations carried out during the 12th and 13th centuries, was largely defused. Thus, although the ecclesiastical authorities did not initially agree with all of Aristotle’s writings, these ultimately became, particularly in the hands of Albertus and Thomas, the foundations of Christian philosophical theology. Not surprisingly, Thomas greatly encouraged Willem of Moerbeke to translate the works of Aristotle, that ancient Greek pagan whom they came to call simply and respectfully the “Philosopher.” Aquinas’ wide-ranging theological approach, formulated for the most part in his massive Summa Theologica and usually denoted simply as “Thomism,” quickly became not only the philosophical arm of Christian theology but also the orthodox theology of the Roman Church. This invaluable achievement brought Thomas the title of Doctor Angelicus and was rewarded by canonization barely 50 years after his death, in contrast to the more terrestrial (or less celestial) Albertus, who had to linger over 650 years before being granted a similar honor. Yet it was the empirical stance of Albertus that ultimately triumphed, and it was the contest between this stance and Aquinas’ philosophical theology that came to underlie the intellectual turmoil of the Renaissance and the scientific revolution of the 17th century.

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Animal Spirit in an Age of Faith But again this is far in the future. In the 13th century, when so much ancient knowledge was retrieved either from Byzantine or, to a far larger extent, Islamic sources, the world into which it was introduced was already thoroughly permeated by Aristotelian ideas.22 Let us now briefly review what Albertus and Thomas, those two leading representatives of scholastic philosophy, had to say about the major theme of this book, animal spirit.

(p.76) Albertus Magnus’ “Psychophysiology” Like earlier scholars, Albertus Magnus presented a three-cell schematic of mental function, but he divided each cell (ventricle) into two compartments. In his major work De animalibus (On animals) he writes: “Further, the brain has three chambers [venter] lengthwise. Each of these has two longitudinal parts, namely right and left, along a line which divides them lengthwise.”23 This modified version of the traditional scheme allowed Albertus to distribute seven internal faculties in the cerebral ventricles: sensus communis, imaginatio, estimatio, fantasia, cogitatio, reminscentia, and memoria. It seems doubtful that Albertus made a schematic drawing of the ventricles for his Philosophia naturalis, but after he died, printed editions, such as the 1506 edition, included one showing split circles based on what he had written (Fig. 5.4). Still, Albertus displayed an awareness of the facts that the ventricles differ in size and also in shape, findings that can be traced back to Galen and others well before Albertus’ time. To quote: The anterior one is large and it is noticeably divided in two parts, namely a right and a left.…The rear ventricle, while smaller than the anterior one, is still large in its own right, for it fills the cavity of a large member there, namely the occiput.…This ventricle is not only smaller than the anterior one but is also smaller than each of the particular anterior ventricles.…The middle ventricle is not so much a ventricle as a sort of transitional passage from the anterior to the rear zone.24 The spirits contained in the cerebral ventricles are described as vaporous and also luminous, due to the very clear nature present in their substance, “just as other bodies,

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Animal Spirit in an Age of Faith outside the animal, are made clear and luminous.”25 Further, “This luminosity is weakened and obscured by unclear, earthy vapors.” A daily example of this darkening takes place after meals, when their vapors ascend to the brain, where they become condensed and thickened by the local coldness; eventually the earthy vapors “block the paths of the animal spirits that minister to sense and motion and prevent the animal power from reaching the exterior senses…Sleep then occurs….”26

The rear ventricle of the brain, in particular, contains at least two kinds of spirit—the motive spirit (spiritus motivus) that goes through the nerves and the nucha,27 and the spirit of the servativa operatio, the function of which is to remember and recall. Apparently these are specializations of the animal spirit, because elsewhere we are told that “after the nerve has been blocked through which the animal spirit passes [to the brain chamber devoted to

Figure 5.4: The “divided” three-cell schematic of the brain to accommodate seven mental faculties (see text), according to Albertus Magnus’ descriptions in his Philosophia naturalis. The drawing, taken from a printed edition published in 1506, is not by Albertus. (Courtesy of the Wellcome Library, London)

memory], memory ceases.”28 Accordingly, and contrary to the “Philosopher,” Albertus concedes that some mental functions are processed at least in part within the brain, even if “the intellect is immaterial and thus does not use an organ.”29 These processes, as summarized in the following paragraphs, are quite elaborate.

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Animal Spirit in an Age of Faith The animal spirit, he explains, flows out from the brain’s ventricles through nerves to the sense organs. Here it is impressed with sensory stimuli, much like wax can be imprinted with a seal, and this “species sensibilis” is carried back up to the first of the brain’s cells. The impression is thus delivered to the first faculty of the mind, the sensus communis, located in the wall of this anterior cell. This first faculty is able to integrate the contents delivered from the various senses, and it can synthesize a perception of a (p.77) unified object—its color, texture, shape, etc.—a process that remains mysterious to this day, and which we know in our times as the “binding problem.” Furthermore, the sensus communis has the ability to control the flow of animal spirit (or in Albertus’ terms, spiritus sensibilis) to the sense organs, thus determining the attention given to various visual objects, sounds, smells and other percepts in the environment. Next in line after the sensus communis, but still in the anterior cell (Fig. 5.4), comes imaginatio, and after that estimatio. Albertus places this last-mentioned faculty in the middle ventricle in animals but in the anterior one in humans. It is responsible for what we would call the instinctive response: the sheep’s flight from an image of a wolf (to use Albertus’ example), or the dog’s pursuit of a hare. In humans, the instinctive response may be tempered by forethought. The second cell in Albertus’ scheme is associated with the faculties of fantasia and cogitatio. The faculty of fantasia allows humans to envision mythological or unmet entities, such as unicorns, satyrs, basilisks, centaurs, sirens, and the like. Cogitatio is closely related to fantasia but involves the application of rational thought. Thus, the faculty of fantasia may toy with the idea of the three angles of a plane triangle adding up to more or less than 180 degrees; cogitatio, on the contrary, determines that the angles of a plane triangle cannot add up to anything other than 180 degrees, and develops from this premise the other axioms of Euclidean geometry. Albertus sees this transference from fantasy to rational thought as passing across the barrier from the material to the immaterial (spiritual) world, from the world of particulars to that of universals. This transference from the world of corporeal things to that of the intellect is controlled, according to Albertus, by Galen’s worm-like valve at the junction between the second and third ventricles (see Chapter 2). Finally, the third ventricle is associated with the faculties of memoria and reminiscientia. Memoria stores the outcome of the progressive work of the two anterior cells, while reminiscientia, an actively directed faculty, is that which recalls memories. It is important to note that, in what today might be called Albertus’ “psychophysiology,” these seven faculties are regarded as located in the solid walls of the cells, while transference of “information” from one cell to another is accomplished by the spiritus animalis. The intellectual activity itself occurs, still mysteriously, in the seemingly homogeneous substance of the brain.

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Animal Spirit in an Age of Faith Albertus’ reputation was so great that his ideas remained highly influential throughout the remainder of the Middle Ages and survived into the Renaissance. His system is, moreover, fairly representative of medieval understanding in the philosophy of nature. Nevertheless, as a convinced Aristotelian, he recognized a peculiar difficulty: how could Aristotle’s psychophysiology be reconciled with the system taught by Galen? To begin with, Albertus faced a problem in discussing the nature of the nerves themselves, for Aristotle and his contemporaries did not distinguish nerves from other whitish strands running between body parts. As it will be remembered from Chapter 1, they lumped sinews, aponeuroses (the whitish fibrous membranes that connects muscle to bone or fascia), and nerves all together under the general term “neura” (neύra). Furthermore, Aristotle was convinced that so far as the “the sinews [neura] of animals” are concerned, “the point of origin is the heart.”30 Reconciling this last statement with the fact, well established by Galen, that the origin of the nerves is from the brain/spinal-cord axis31 posed a major challenge that threatened to undermine the coherence of the Church’s natural philosophy. Aristotle would have to be declared mistaken on this, thus opening the way for doubt throughout the complete system. Albertus solved the riddle with a fudge. “It ought to be known, then, that beyond doubt the nerves branch off from the brain,” he wrote, but added “that the first origin of all of them is the heart via a nerve-filled substance which comes from the heart to the brain….”32 When pressed, Albertus, like Avicenna before him, attempted to circumvent the fudge by addressing it on two levels. “One must reply,” he writes, “as was done earlier regarding the veins, that origin is spoken of in two ways: one is virtual and radical, and this is how the nerves and all the official parts of an animal arise from the heart; another is corporeal and immediate, and this is how the nerves arise from the web of the brain itself and from its nucha.”33 He tries to have it both ways. He wants to eat his cake and have it too. He wants to agree with Aristotle’s philosophical system in which the heart is the center of the body’s physiology and at the same time agree with the anatomists who, following Galen, showed that the nerves, as seen in dissection, arise from the brain and spinal cord. This Avicennan/Albertian ambiguity has resonated down the ages.34 William Shakespeare, in the English Renaissance, was still unsure of where emotion, at the least, is located and sustained, and asks in the Merchant of Venice: Tell me where is fancy bred, Or in the heart or in the head?

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Animal Spirit in an Age of Faith How begot, how nourished?

The Thomist Synthesis While Albertus legitimized Aristotle’s natural philosophy and largely reconciled him with Galen on physiological matters, his pupil Thomas launched a wideranging endeavor to blend Aristotelian philosophy with Christian doctrine. His basic proposition was that all of Aristotle’s conceptions about the world were essentially correct, except that, having lived more than three centuries before Christ, he was obviously unable to include in his system the superior reality that the Savior revealed to humanity. In Aquinas’ Christianized Aristotelianism, humans are uniquely placed at the frontier of two vastly different domains: the corporeal world, mostly consistent with Aristotelian physics, and the spiritual (p.78) realm, as conceived by the Church. Accordingly, “it was fitting that the human body should be made of the four elements, that man might have something in common with the inferior bodies, as being something between spiritual and corporeal substances.”35 The main problem was to show how the spiritual and the corporeal parts interact to form a functional entity, capable of behaving as required in order to pass St. Peter’s portal and at the same time being able to cope with the myriad details of everyday life. Fortunately the key to this issue, like countless others, had been given centuries ago and in a most convincing way by Aristotle himself. In Aquinas’ words: “It is true that it [the soul] moves the grosser parts of the body by the more subtle parts. And the first instrument of the moving power is the breath, as the Philosopher says.”36 Aquinas refers here to Aristotle’s De motu animalium, where pneuma acts as the link between the soul, centered on the heart, and the body at large.37 Yet Aquinas, as would be expected, focused mostly on theological interpretations of the soul, rather than on its anatomical location. He states that “there is no need to assign more than four interior powers of the sensitive part [of the soul]— namely, the common sensorium [sensus communis], the imagination, and the estimative and memorative powers”38—but he does not enter into details about the brain, its ventricles, or any other location for these powers. He probably relied on Albertus’ works to cover such ground since, despite all of his veneration for the “Philosopher,” Aquinas was not primarily interested in the philosophy of nature. Thus, for example, perhaps because he was concerned with a transcendental reality totally unknown to Aristotle, the Doctor Angelicus appropriately devoted more of his time to analyzing the movements of angels than to those of animals.39

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Animal Spirit in an Age of Faith Still, in a rare exception and like Alfred of Sareshel before him,40 Aquinas examined the enigmatic, apparently autonomous movement of the heart, the seat of the soul from which in turn, as the “Philosopher” taught, the rest of the motions of the animal body proceed. He concludes, in standard Aristotelian fashion, that “the movement of the heart is natural because it results from the soul, inasmuch as it [the soul] is the form [i.e., the structure] of one particular body and primarily of the heart.”41 In other words, the heart moves by itself because it is built to do that, or, more simply, because it is the heart! This takes us to the second line of intellectual evolution mentioned at the beginning of this chapter—that is, to a growing passion for learning not only from old books copied many times throughout the centuries but also from the things themselves, from the book of nature. And one of the most remarkable developments in this direction was undoubtedly the direct inquiry into how the human body is really organized internally. But before we turn to the rebirth of human anatomy in the late Middle Ages and Renaissance, it is important to emphasize that, in addition to Albertus’ Aristotleflavored natural philosophy and Thomist theology, the medieval intellectual world was also awash with religious concepts derived from the Holy Scripture.42 These concepts made no reference to the nerve physiologies of the Greek, Roman, and Islamic medical writers. In particular, Christians assumed that the human spirit had none of the material connotations of the physiologists, since it was literally “God’s breath” (Genesis 2:7), immaterial and immortal. This religious meaning was strongly present throughout the Age of Faith. Augustine, it will be remembered from Chapter 3, flatly denied any physical characteristics to the human soul. Thus, when perception, cognition, and memory were becoming firmly associated with the various ventricles of the brain in the Western medical tradition, the ontological status of “spirit” tended to remain uncertain. James Bono, a modern historian of ideas, writes that during the Middle Ages and later, in the Renaissance, the term “spiritus” was transmitted along a whole spectrum of frequencies, from “a material entity—a sort of medium, and an instrument of life located somewhere just above elemental matter, yet far short of the dignity and immateriality of the soul” to, at the other extreme, a “quasi-divine substance, the unique intermediary and sole repository of the life-giving activity of the body.”43

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Animal Spirit in an Age of Faith It is, of course, the first of these connotations of “spiritus” that medieval authors writing on medical matters had in mind when they described the psychological functions of the cerebral ventricles. The notion was very much alive as the medieval period drew to a close, giving way to the Renaissance. It appears illustrated, among many other delightful woodcuts, in the 1503 edition of the Margarita philosophica (The Pearl of Wisdom), a widely read compendium of contemporary knowledge by the Carthusian monk Gregor Reisch (c. 1467–1525; Fig. 5.5). Reisch’s text proved so popular that it was republished many times during the 16th century. By then, however, previous knowledge was under a comprehensive process of revision on many fronts and with different methodologies. Students were not quite so willing to accept the traditional teachings of authorities of the past, a trend that would become even more significant during the Renaissance. Indeed, as we shall see below, Leonardo da Vinci (1471–1511) outlined the shapes of the cerebral ventricles in far more a realistic way than his predecessors in drawings made at about the same time as Reisch published the first edition of The Pearl of Wisdom.

(p.79) The Rebirth of Human Anatomy After Galen’s death at the beginning of the third century CE, the practice of dissection, especially human dissection,

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Animal Spirit in an Age of Faith fell from favor in the West.44 There is some evidence, as noted in Chapter 4, that it was practiced to a small degree in medieval Islam, but it was frowned upon by religious authorities in the Latin West, not only as a deeply unpleasant practice but also as a desecration of the human body, God’s final and most excellent handiwork. It seems that, for centuries, anatomy was taught to aspiring physicians by means of five traditional figures illustrating the skeletal, muscular, nervous, arterial, and venous systems. There is evidence to suggest that these manikins originated in late antiquity and were hardly altered through successive centuries until the tentative rebirth of dissection in the 12th century.

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Animal Spirit in an Age of Faith Figure 5.6 shows the depiction of the nervous system in the fivefigure series. Note how similar it is to (though not identical with) the nervous system depicted in Avicenna’s Canon (Fig. 4.7).

Figure 5.5: Roles of the 3 “cells” or ventricles of the brain in handling the classic powers of the sensitive soul, as illustrated by Gregor Reisch in his Margarita philosophica (Freiburg: Johann Schott, 1503). The lines drawn from eye, nose, tongue, and ear show that information from all these sense organs is delivered to the first cell, the seat of the sensus communis. Reisch also inserted “fantasia” and “imaginatio” into this cell. The choroid plexus (vermis) connects this anterior compartment with the middle cell, which is devoted to cogitatio and estimatio (judgment). The third and most posterior cell is in turn concerned with memoria.

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Animal Spirit in an Age of Faith Then, some time at the beginning of the 12th century, anatomy began to be practiced in the nascent medical school at Salerno. At first this practice was limited to animals, (p.80) especially the pig. Indeed, the earliest medieval “dissection manual” that has come down to us dates from the early 12th century and describes the anatomy of that animal.45 The manual, wrongly attributed to an unknown person named Cophus, and hence commonly known as the Anatomia Cophonis, describes how to

Figure 5.6: The nervous system as depicted in a “five-figure series” of ancient and medieval anatomy teaching. The head is shown in two orientations, Cubist-like fashion. The face is seen in the upper part of the figure, with the two eyes staring out of the picture. The cranial cavity is shown in the lower part of the “head.” It appears to contain four circles (ventricles?), the two on the left connected to the two on the right by a rectangle. This is labeled as the center of the brain. The other writing identifies the cranial nerves recognized at that time (from Garrison, 1926, p. 34).

dissect the animal and gives names for the various parts revealed. Its author does not have much to say about the brain, confining himself to a description of the meninges and the brain’s surface, and going on to a brief anatomy of the eye and optic nerve. The next anatomical text known to exist in the Latin West, also deriving from the Salernitan medical school, is the Anathomia by Master Nicolai the Physician in about 1200 already mentioned at the beginning of this chapter.46 We noted that although it purports to be a first-hand dissection of the human body, it is still largely a repetition of what Galen had taught nearly a thousand years earlier. It is, nevertheless, carefully organized with its various terms defined, showing the influence of Nicolai’s scholastic education. It is not difficult to realize that, with lack of adequate preservation methods and scant or no first-hand experience of dissection, little understanding of the intricacies of human anatomy was available to physicians, let alone philosophers, during most of the medieval period. This was probably no great drawback for the general practitioners of the period. For, as historian David Lindberg points out, medieval physicians had little need to know detailed anatomy, as their work consisted mainly of adjusting diets and prescribing and mixing herbal remedies.47 On the other hand, such ignorance was a fertile ground for the proliferation of entirely fanciful ideas about human anatomy, including misguided speculations concerning the nerves and the central nervous system, and their relations to behavior or psychological faculties. The practice of actually trying to find what is there began in earnest a little later, stimulated by Frederick II (1194–1250), who viewed himself as a direct successor of the Page 20 of 49

Animal Spirit in an Age of Faith ancient Roman emperors, and who controlled the medical school at Salerno. Deeply interested in natural philosophy and learning, he decreed that no surgeon could practice his craft before studying anatomy for at least 1 year. He also seems to have broken with the past by ordering a public dissection of a human cadaver every 5 years, although this claim has not been easy to validate.48 Still, like so much else in those times, Frederick’s advanced thoughts about medical education spread rapidly across what is now Italy, from Salerno in the south to Bologna and then Padua in the north.

Figure 5.7: A prosector (usually a barbersurgeon) instructed by a physician (in the chair) during an anatomical demonstration. Although this woodcut is taken from Mondino’s Anathomia corporis humani, republished in Ketham’s Fasciculus medicinae in 1493, Mondino is known to have practiced dissections himself in the early fourth century. This sound custom was not to last for long, however, as inferred from Vesalius’ testimony. By the time this figure was made, the highly educated, Latinate anatomy professors disdained to do their own anatomical demonstrations, often leaving that obnoxious business to barber-surgeons.

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Animal Spirit in an Age of Faith According to the great historian of science George Sarton, the Bolognese anatomist Mondino de Luzzi (c. 1270–1326) was the first to use the dissection of human cadavers to illustrate his anatomical lectures at Padua.49 Mondino’s teachings were published in the first example of a human dissection manual to come down to us, the Anathomia corporis humani. This guide was written in 1316 and first printed in Padua in 1478.50 Although this first printing contained no illustrations, many of the subsequent editions included one or more woodcuts (Fig. 5.7). This landmark text was widely used throughout the succeeding centuries, and over 40 editions are known to exist. Both Leonardo51 and Berengario da Carpi (c. 1460–c. 1530) consulted it at the beginning of the 16th century (see below), before it eventually fell into desuetude later in the Renaissance. (p.81) Interestingly, Mondino took the human body to consist of three major regions, each containing its characteristic “members.”52 These three regions are the skull, which contains the “animal members” (membra animata, or belonging to the anima [i.e., the sense organs and those constituting the encephalon]); the thorax, which contains the “vital members” (membra vitalia, like the heart and lungs, etc.); and the abdomen, which contains the “natural members” (membra naturalia [i.e., the liver, stomach, intestines, etc.]). Can we see here the influence of Plato’s Timaeus, which we discussed in Chapter 1, with its similar tripartite physiology?53 Despite this original and courageous effort to examine human anatomy directly, the special difficulties of dissecting the head are probably responsible for Mondino’s account of the brain, which he sees, once again, as divided into three ventricles or cells. Following tradition, he assigns the sensus communis to the anterior ventricle, imagination to the middle, and memory to the posterior. Mental operations are controlled by the motions of the Galenical “membranous worm” between the middle and posterior ventricles. But while Galen’s influence is recognizable in this psychology, Mondino was also open to Aristotle’s thoughts. The brain, he writes following the “Philosopher,” also has the function of cooling the blood.

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Animal Spirit in an Age of Faith Indeed, he tried very hard to accommodate Aristotle’s cardiocentric psychology into his teaching. He argued that, because the two recurrent laryngeal nerves pass very close the heart,54 they are well suited to pick up the heart’s commands and carry them to the brain. This theory carried some conviction for, since Galen’s time, it had been known that the cutting of these nerves destroyed not only the ability of pigs to grunt and squeal, but also that most definitive of human abilities, the power of speech.55 In this popular variant of Avicenna’s scheme, the heart remains the true source of willed activity and central for nerve and muscle functions.56 Thus, we can see in Mondino’s writings a continuation of the centuries-long wrestling between the evidence found on the dissection table, on one hand, and the theoretical convictions derived from reading the classical texts. Although there is little doubt that Mondino’s Anathomia is based largely on his own dissections, it was not until the middle of the 14th century that the practice received a broader official sanction. Public dissections by Gentile da Foligna (c. 1285–1348) commenced formally in Padua in 1341,57 and north of the Alps a statute initiating a biennial dissection of a human cadaver was published at Montpellier in 1377.58 Even so, the possibility of a medical student seeing an anatomy in the 14th and 15th centuries, even from far back behind a crowd of society notables, was initially restricted to no more than once a year. Nevertheless, the trend to find out anew how the natural world really works was under way, and quite a few surprises were in store for those interested in how the human body is built and how this related to function.

Neuroanatomy in the Renaissance Leonardo’s anatomical drawings are all fascinating, and among the most fascinating—especially for historians of biology, the behavioral sciences, and medicine—are those depicting the brain’s ventricles. In a large sketch dated about 1490 (Fig. 5.8), he showed the conventional view of the ventricles in both vertical (sagittal) and horizontal section. The optic nerves run from the eyes to the anterior ventricle, with the middle and posterior ventricles following as a connected series behind. All three ventricles are sketched in the traditional way as globular vesicles.

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Animal Spirit in an Age of Faith In the following few years he started to produce a totally different image of the cerebral ventricles, until between approximately 1504 and 1507 he used a sculptor’s technique that enabled him to obtain a far more accurate representation of their true morphology (Fig. 5.9). He injected the ventricles with molten wax, while draining the existing contents through an outlet; then, after allowing time for solidification, he removed the surrounding brain tissue. Although he is reported to have dissected over 30 human bodies,59 it is not always clear which brains—human or animal(s)—he injected and examined. Hence, he writes of having injected the brain of an ox, but the structure of the ventricles in his drawings are those of a human brain, not those of a quadruped. It has been suggested that he dissected the brains of both humans and oxen, and then drew a composite sketch amalgamating the best of both.60 However it was done, Leonardo produced the first realistic images of what the ventricles really look like in the mammalian brain, his drawings even showing how the cavities are connected. In this respect, his artwork represented a major break with the cartoons of past, which did not reflect the anatomical reality. But two additional things are worth noting in this context. The first is that Leonardo was not able to make a clean break with the idea that the three ventricles serve different functions of mind. It is interesting to note, however, that he labels the ventricles in an unorthodox manner. The first he labels “imprensiva” (perception), the middle “sensus communis,” and the third “memoria.” Leonardo’s location of the sensus communis in the middle ventricle is partly due to its central position61 and partly to his extensive dissections (p. 82)

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Animal Spirit in an Age of Faith revealing that most cranial nerves are associated with that part of the brain.

Unfortunately, Leonardo’s anatomical drawings disappeared from public view soon after his death at Amboise, France, in 1519. The original works passed through various hands, including those of his nephew, Orazio Melzi, the sculptor Pompeo Leoni, the Earl of Arundel, and the English Royal Collection, until the Scottish anatomist William Hunter (1718–1783) saw them and arranged for their publication in the 18th century. Hunter died before this was achieved and Leonardo’s anatomical drawings did not enter the public domain until the 19th century.

Figure 5.8: Leonardo’s early drawings (c. 1490) of vertical and horizontal sections through head and eyes. The three

Although the disappearance of traditional cerebral ventricles are clearly Leonardo’s anatomical shown as a series of vesicles (Clark drawings prevented them from 12603r; from O’Malley and Saunders, exerting any significant 1983, plate 142, p. 330). influence on anatomy in the 16th century, their rediscovery allows a glimpse of the ideas circulating at that time. In particular, they open a window on the theory of neuromuscular physiology prevalent in those years, seen through the eyes of an experimentalist with an inexhaustible curiosity and thirst for novel knowledge. Let us briefly look, then, at some of his more interesting remarks.62 Since one of the main reasons for Leonardo’s initial attraction to anatomy was to present a true and exact depiction of human and animal bodies in his art, he must have (p.83)

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Animal Spirit in an Age of Faith been particularly interested in how muscles function. Apparently he did not see any difficulty in accepting the standard theory, for on a page with extensive text and a few small anatomical drawings, he writes of “the wind [vento] which thickens the muscles to shorten them and which arises from the lung that drives the vital spirits that command the nerves.”63 On another sheet, accompanying a large drawing of the vertebral column and spinal nerves, Leonardo writes presciently of the neuromuscular system using concepts that only became orthodoxy in the 17th century:

The substance of the medulla enters for some distance into the origins of the nerves and then follows the hollow nerve as far as its terminal ramifications. Through this perforation [i.e., the duct within the nerve] sensibility is carried into each muscle. The muscle is composed of as many other minute muscles as there are fibers into which this muscle can be resolved, and each of the smallest of these muscles [i.e., fibers] is covered by an almost imperceptible membrane into

Figure 5.9: Leonardo’s later drawings (c. 1504–1507) of the cerebral ventricles, as deduced from wax injection. The lefthand drawing shows a vertical crosssection of the brain, whereas in the righthand part of the plate the brain is seen after being vertically cross-sectioned from the top and then opened like a book. The bottom figure presents the inferior surface of an intact brain, in which a multi-branched structure is depicted, this being the rete mirabile. It is here, according to Galen, that the vital spirit coming from the heart is distilled into animal spirit. This suggests that at least this brain was in fact that of an ox, since the rete mirabile does not exist in the human brain (Clark 19127r; from O’Malley and Saunders, 1983, plate 147, p. 340).

which the terminal ramifications of the aforementioned nerves are converted. These obey in order to shorten the muscle with their withdrawal and to expand it again at each demand of the sensibility which passes through the hollow cavity of the nerve.64

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Animal Spirit in an Age of Faith Leonardo believed that two tubes running parallel to each other on each side of the vertebral column are the conduits for the sense of touch and also “the cause of motion, the (p.84) origin of the nerves,” and “the passage for the animal powers.”65 These tubes, which we now recognize to be entirely hypothetical, became the focus of his attention until he realized that it was the spinal cord where the center of vertebrate life seemed situated. He repeatedly tested this idea by means of experiments: The frog retains life for some hours when deprived of its head, heart and all its intestines. And if you prick the said nerve [i.e., the spinal medulla] it suddenly twitches and dies. All the nerves of animals derive from here [i.e., the spinal medulla]. When this is pricked, it [the frog] immediately dies.66 And again, here is his quite reasonable conclusion: The frog immediately dies when its spinal medulla [midolla della sciena] is perforated. And previously it lived without head, without heart or any entrails or intestines, or skin. It thus seems that here lies the foundation of motion and life.67 Is Leonardo here, as elsewhere, far ahead of his time? Or is he simply rehearsing ideas that were circulating among the savants of his era? Whichever proves to be the case, it is regrettable that his anatomical drawings and physiological thoughts disappeared from view for so many years. Indeed, the two paragraphs quoted above altogether escaped the notice of an otherwise excellent 20thcentury study of the role that frogs have had in the history experimental physiology.68 Nevertheless, it has to be remembered that Leonardo was a polymath and not a professional anatomist. Others,

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Animal Spirit in an Age of Faith who were, also began to move the subject out of the medieval gloaming into the light of day. Foremost among the dissectors at the beginning of the 16th century was Jacopo Berengario da Carpi (c. 1460–c. 1530; Fig. 5.10), a member of the faculty of the highly regarded University of Bologna, where he performed many dissections of human bodies.69 Berengario’s first publication was a treatise on head wounds (1518), and he followed this with an important commentary on Mondino’s Anathomia, including the original text, which he published in Bologna in 1521. A year later he published A Short Introduction to Anatomy,70 designed to be used by medical students. Both texts show evidence of first-hand observation and, even more importantly, included a number of first-hand

Figure 5.10: Berengario da Carpi (1460– 1530), by an Emilian painter of the 17th century.

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illustrations of his dissections. They are often regarded as the first modern textbooks of anatomy.

Berengario’s turning away from book learning towards personal observation led him to question the existence of a structure that played an important role in animal spirit theory from the time of Galen onwards: the rete mirabile discussed in Chapter 2. He writes, “I have never seen this net…I have given many…reasons [for the non-existence of this net] in my Commentary on Mundinus [sic].”72 He also failed to find other structures mentioned by Galen and his Islamic followers, thus opening a door that had been closed for over 1,300 years. Hence his attitude to the ancient texts was far from mere dutiful acceptance. He trusted his own eyes more than the books of the past: “sense perception,” he writes, “is the judge in these matters.” The following quotations further serve to show his cast of mind: “And let sense perception agree with this text and thus let those who write books on anatomy also not trust in the authorities but in their sense perception as I do and shall do.”73 And even more to the point, he writes of “Galen with his followers whose opinion I always maintain, except when sense-perception disagrees with him.”74

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Animal Spirit in an Age of Faith Although sentiments such as these had been expressed by some of the Islamic physicians we discussed in Chapter 4, it is clear that by the beginning of the 16th century Western physicians and natural philosophers were at last turning (p.85) from ancient medical books and commentaries on those books to the book of nature itself. Nevertheless, exactly what the scalpel revealed beneath the human skin remained difficult to understand. Preservatives were in their infancy and cadavers were difficult to obtain. And as is so often the case, anatomy, or what could be seen, was preceding physiology, or knowledge of how things work. By all accounts, Berengario was not a pleasant man; indeed, rumor had it that he had practiced vivisection on two Spaniards suffering from syphilis.75 Still, in his attitudes toward book learning versus direct observation, and in his rather crude attempts to illustrate what he saw in his dissections with figures in his anatomy texts, he might be said to have played John the Baptist’s role to an even greater anatomist. That greater anatomist was the bold Flemish genius Andreas Vesalius, the “great instaurator” of human anatomy in its modern phase.

Vesalius: The Human Body Revealed Andreas Vesalius (1514–1564; Fig. 5.11) was born in 1514 in Brussels, then a part of the Netherlands, into a family that for generations had been involved in science and medicine. He began his medical education near home at the University of Louvain, then studied in Paris, and afterwards, when war threatened, returned to Louvain to continue his training. His curriculum, especially in Paris, was a conservative one. Galen’s authority was considered absolute. Moreover, although animal dissections were performed, most notably under the direction of Jacobus Sylvius (1477–1555), human dissection was proscribed. It seems, however, that some st

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Animal Spirit in an Age of Faith udents, including Vesalius, eager for first-hand experience, took to pilfering human bones from the gallows and cemeteries for their own clandestine studies.

In 1537, Vesalius moved to Padua, where he passed his final medical examinations and accepted the chair of surgery. This was, at that time, the foremost medical school in Europe and it attracted students from all over the continent. Vesalius’ duties included giving surgical lectures and anatomical demonstrations, for which purpose the authorities provided him with bodies of executed criminals. Literally taking matters into his own hands, he cut open these Figure 5.11: Andreas Vesalius (1514– bodies, studied them carefully 1564), from the frontispiece of De humani and took notes, and in 1538 corporis fabrica, 1543. published his Tabulae anatomicae sex, a set of six large plates showing the vascular system and skeleton. On one of these plates he dutifully included the rete mirabile, which he continued to associate with the transformation of the vital spirit to the animal spirit in accordance with Galenic tradition. Five years later, in 1543, he published his masterwork, De humani corporis fabrica. This magnificent volume is regarded, with reason, as the foundation work of modern anatomy. It is based on his personal experience with probably hundreds of human dissections and similar numbers of animal vivisections. It is also replete with anatomical illustrations drawn directly from his dissections, some probably done by his countryman, artist Jan Stephen van Calcar (1499– 1546).76 With the Fabrica we have finally broken through from the medieval world of copyists and flights of anatomical fancy to the “light of common day.” One of the best examples of this clarification can be found in his account of brain structure. In Chapter 1 of Book VII of the Fabrica, Vesalius reflects, in a regretful mood, on how he was taught the doctrine of the cerebral ventricles by his early-16th-century teachers:

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Animal Spirit in an Age of Faith I well remember how when I was following the philosophical course at the Castle School, easily the leading and most distinguished school of the University of Louvain…the brain was said to have three ventricles. The first of these was the anterior, the second the middle and the third posterior, thus taking their names from their sites; they also had names according to their function. Indeed those men believed that the first or anterior, which was said to look outwards towards the forehead, was called the ventricle of the sensus communis because the nerves (p.86) of the five senses are carried to it from their instruments, and odors, colors, tastes, sounds and tactile qualities are brought into this ventricle by the aid of those nerves. Therefore, the chief use of this ventricle was considered to be that of receiving the objects of the five senses, which we usually call the common senses, and transmitting them to the second ventricle, joined by a passage to the first so that the second might be able to reason and cogitate about those objects; hence cogitation and reasoning were assigned to the latter ventricle. The third ventricle was consecrated to memory, into which the second desired that all things sufficiently reasoned about those objects should be sent to be suitably deposited. The third ventricle, as it were moist or dry, either more swiftly or more slowly, engraved them as into wax or harder stone…Furthermore, that we might more aptly consider each thing that was taught, an illustration was shown us, taken from some Philosophic Pearl [i.e., Gregor Reisch’s The Pearl of Wisdom], presenting to our eyes the aforesaid ventricles, which each of us studied very carefully as an exercise and added a drawing of it to our notes.77 In stark contrast to Reisch’s picture, the illustrations of the cerebral ventricles shown in the Fabrica (Fig. 5.12) are evidently drawn from first-hand observation. The medieval and early Renaissance three-cell circular schematic, which for so long had been a teaching tool, is nowhere to be seen! Moreover, this breakthrough in anatomy is accompanied by a change in attitude towards knowledge. For Vesalius openly declares that, once having examined the brain minutely both by dissection and vivisection (of animals), he is unable even to suggest what might give rise to “imagining, reasoning, thinking and remembering (or however else you like to subdivide and enumerate the powers of the soul-in-chief, in conformity with someone else’s teachings).”78 All he could guess from comparative studies is that, because the cerebral ventricles in infrahuman mammals are similar in number and distribution to those in humans, such cavities could hardly be the source of human intellectual superiority. In his well-chosen words, “we clearly see in dissecting that men do not excel those animals by any special cavity.”79

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Animal Spirit in an Age of Faith Vesalius is in no doubt that the ventricles contain an “aqueous fluid” (although whether he identifies this with animal spirit he does not say) and not some mysterious spiritual “wind.” He writes that animal spirit is distributed through the nerves to the sense organs and the muscles.80 He describes the nerves as “long rounded organs that have no perceptible cavity at their center…[which] convey animal spirit from the brain, fomenter of the animal faculty, to parts of the body.”81 He does not spend time theorizing about how this conveyance is achieved, “whether through minute channels in the nerve, or along the sides of the nerve like light against a column.” But he is quite clear that all nerves originate from the encephalon and “spinal marrow” and in no case arise from the heart. Vesalius was uncertain about the nature of the animal spirit. As we noted above, he had found the ventricles to be filled with a watery fluid hardly different from other such fluids.82 Further, and like Berengario before him, he could find no evidence that the marvelous “net-like plexus” (rete mirabile), which Galen and his followers placed at the base of the brain, and which played such an important role in their physiology, could be found in humans.83 His dramatic confession of this failure provides us with some feel for Vesalius’ anguished struggle with the contradictions between timehonored tradition and the revelations of the dissection table.

Figure 5.12: Ventricles of the human brain, from Vesalius’ Fabrica, 1543.

His embarrassment was acute, since as mentioned above he had depicted the rete mirabile in a drawing in his earlier Tabulae anatomica. At the beginning of Chapter XII in book VII of the Fabrica, however, he feels compelled to agree with Berengario that no such structure is present in human brains. He mentally kicks himself for having been stupid enough in his younger days to have believed it existed. “I was so besotted by Galen,” he writes, “that I had never undertaken to demonstrate a human head without the head of a lamb or ox at my public dissections…I imposed upon my audience by demonstrating from a sheep’s head something I had never found in a human one.”84 Despite the (p.87) strong terms of this disclosure, however, Vesalius did include a sketch of the rete mirabile in the Fabrica, writing that he is presenting it in agreement with what Galen had described, so as to illustrate that he is aware “of the difference between these animals [sheep and oxen] and man in this respect.”85 Page 32 of 49

Animal Spirit in an Age of Faith In the Preface to the Fabrica Vesalius blames theoretical book learning and second-hand teaching methods for the prevailing general ignorance about human anatomy. He writes of that detestable procedure by which usually some conduct the dissection of the human body and others present the account of its parts, the latter like jackdaws aloft in their high chairs, with egregious arrogance croaking things they have never investigated but merely committed to memory from the books of others…The former so ignorant of languages that they are unable to explain their dissections…so that in such confusion less is presented to the spectators than a butcher in his stall could teach a physician.86 It cannot be said that anatomical teaching changed abruptly throughout Europe after the publication of the Fabrica. In fact, the text was treated harshly in some places, including Paris, where his conservative teacher Sylvius looked upon it as blasphemy and Vesalius as a madman. Nevertheless, it was praised by many and the winds of change began to blow. New attitudes and new approaches to the functioning of the body, to its physiology, were beginning to

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Animal Spirit in an Age of Faith appear. The time-honored ventricular or “cellular” psychology began to wither away. The equally time-honored notion of animal spirit, however, persisted far longer, although it was freshened up with a more elaborate theory.87

The Beginning of a New Era in Physiology: Jean Fernel Jean François Fernel (c. 1497– 1558; Fig. 5.13) was born at Montdidier in France in about 1497, the son of an innkeeper. The family moved to Clermont, just outside Paris, when Jean was 12 and it was there he spent his school years. From Clermont he went to Paris for his university education, graduating in 1519 with an MA degree. He seems to have felt dissatisfied with his university work, for he left the academic world to spend the next 5 years almost as a recluse, studying and attempting to master a wide range of subjects, especially philosophy, Figure 5.13: Jean François Fernel (1497– astronomy and mathematics. It 1558), from his Medicina, 1554. was only in 1524, when his father lost patience with him and withdrew his financial support, that he began to earn his keep by lecturing in Paris, and it was then that he began to study medicine. His main interest during these early years was, however, still strongly biased toward the occult, and his first publications were in astrology. But it was at this time, when lecturing on philosophy and investigating astrology and magic, popular subjects at the time, that an important event occurred in his private life: he married. His father-in-law, a Parisian senator, insisted that the young man would become more serious about his medical studies and apply his abilities to support his wife and family.

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Animal Spirit in an Age of Faith This Jean did to remarkable effect. He obtained his medical qualifications in 1530 and within 6 years was one of the most influential physicians in France.88 Students flocked to hear his discourses and he made his name at court by saving the life of the Dauphin’s mistress, Diane de Poitiers (1499–1566). He was appointed to the chair of medicine in Paris in 1534, and after a further brilliant and tumultuous career died in 1558, leaving his biographer Guillaume Plancy (c. 1514–1568) to edit and see through the press the full text of his Universa medicina (which included the Physiologia). The book was finally published 9 years later in 1567. Fernel began writing the De naturali parte medicinae in 1536, addressing a large number of medical topics, including anatomy, the temperaments, the spirits, the faculties of the soul, the bodily humors, procreation and embryology. This great work was first published in 1542 and later, renamed Physiologia, formed the third part of the Universa medicina, which Guillaume Plancy published in 1567.89 It was (p.88) with this publication that the term “physiology” largely assumed its modern meaning and entered the scientific language. Fernel’s text was studied by medical students until William Harvey’s discovery of the circulation of the blood in 1628 rendered it obsolete. Although still thoroughly immersed in the time-honored writings and ideas of Aristotle and Galen, it set out the medicine of his era.90 Among other things, he took the animal spirit doctrine for granted. Indeed, he devoted the entire fourth book of his text to the topic, where he writes: “The ventricles and inner chambers of the brain abound with a great quantity of this [animal spirit], and from them it flows forth, as from a running spring, through the nervous channels, then into the sensory instruments, then into the motor muscles.”91 Yet some things have changed. Fernel no longer discusses the ventricles as the anatomical bases of psychological faculties. No longer do we read that the first ventricle has to do with the sensus communis, the second with cogitation, and the third with memory. Instead they are regarded as part of a hydraulic system involved in pumping the animal spirit through the nervous system:

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Animal Spirit in an Age of Faith the body of the brain is in unending movement, like the heart, of itself and its own volition, now expanding and now contracting. Nature has therefore left empty space between the meninges, the amount required for cerebral expansion. While the brain contracts in the course of this movement, and narrows its internal cavities by squeezing their sides, spirit pours out from the anterior ventricles, both into the posterior ones and into the instruments of the senses. But when it enlarges and opens itself out, from the arteries of the structures it entices and pulls vital spirit, and from the nasal cavities, air. At that very moment, the pathway that leads from the third ventricle to the posterior one closes down completely, and is blocked by the descent of the process that is named after a worm [vermix of the cerebellum], settling and slipping down between the “buttocks” [corpora quadrigeminus superior of the cerebellum], so that no spirit can retrace its path from the posterior ventricle to the middle [third] one. The reverse occurs when the brain contracts: the process [vermix] is raised, and the “buttocks” themselves draw further apart, so that the way is more open for spirit to run from the third ventricle into the fourth. The “worm” and the “buttocks” contribute as much to the brain as the valves do to the heart.92 It can be seen from this passage that Fernel is still immersed in Scholastic book learning. He is profoundly aware of Aristotle’s philosophy. But, despite his devotion to the “Philosopher,” he, like Vesalius, is quite clear that the nerves originate in the brain and not in the heart. He had to argue against what he called “a mob of sophists” (i.e., Aristotelians), who still held to the theory propounded by Avicenna and then Albertus several centuries earlier, which held that it can be demonstrated by philosophical reasoning that all powers emanate from the heart. “Unbelievably crazy!” he writes.93 The Aristotelian philosophy, at least the part pertaining to nature as taught by Albertus and other Scholastics, was, however, already living through the last decades of its lengthy reign. A powerful new wave of thought, vigorously led by independently minded intellectuals, was about to alter forever the whole intellectual scene. Fernel can be seen as a harbinger of this wave of new thinking. Although he started as a thoroughgoing Galenist interested, moreover, in the occult and magic, he became more skeptical as he grew older. As his first biographer, Guillaume Plancy, remarks, he came to value ever more highly the findings of practice and observation.94 He started as an occultist and ended by condemning astrology and similar speculations, and we can, perhaps, see in his life trajectory the onset of the kind of new thinking that characterized the scientific Renaissance.

Telesio: “The First of the Moderns”

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Animal Spirit in an Age of Faith Fernel was not the only thinker during the 16th century who felt the tensions between old and newer ways of thinking, tensions with important social and scientific ramifications. The old worldview formed a coherent whole: remove one element and the whole structure might come crashing down. Galileo famously found this out in the early part of the next century, being confined to perpetual house arrest for his pains. But the campaign against the old ways of thought was already at work, as we have seen, well before Galileo. It is represented not only by Fernel and similar thinkers, but even more prominently by the English essayist and statesman Francis Bacon (1561–1626). Bacon went so far as to charge the “Philosopher” with having “corrupted natural philosophy by logic.”95 Bacon himself, however, followed the lead started by the Italian natural philosopher Bernardino Telesio (1509–1588; Fig. 5.14), whom he called “the first of the moderns.” This iconoclast naturalist, a well-read nobleman from Calabria in southern Italy, became increasingly uncomfortable with the clouds of Aristotelian wordiness suffusing Scholastic philosophy. Instead, he left the university to become an independent scholar advocating the study of the world directly, through observation, without preconceived notions about how it might be shoehorned into Aristotelian natural philosophy. The result of this fresh approach was published in 1565 with the title De rerum natura juxta propria principia (“On the Nature of Things According to Their Own Principles”). When considering the living world, Telesio found Aristotle’s concept of the soul as the form of the body untenable, and kept only the idea that spirit, or pneuma, was the (p.89) general instrument that produces all changes collectively known as “life.” Yet the Telesian spirit is considerably more independent than the Aristotelian one—which is always subordinate to the soul—as well as definitely corporeal,

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Animal Spirit in an Age of Faith since it is derived from semen and is nourished by air and vapors from the food.96 Nor is it divisible into separate varieties, as in the traditional Galenic physiology. Instead, Telesio argues that a strict continuity of one and the same spirit is required for overall coordination of different bodily functions. This unitary spirit causes all body parts to move in such a way that they act in unison, as a whole. Impulse transmission along the nerves follows the principles of fluid mechanics. Thus, for example, a particular motion of the comparatively large amount of spirit contained in the cerebral ventricles is communicated to the peripheral body parts, just like motion is transferred from water to water, or air to air.97

Similarly, Telesio maintains that spirit is responsible for bringing information from the various senses to the brain. It is, however, spirit located in the brain that experiences and judges this “information” as sensation. That which benefits the organism energizes this spirit and is felt to be good, while that which is harmful is

Figure 5.15: Francis Bacon (1561–1626). (Courtesy of the Wellcome Library, London)

Figure 5.14: Bernardino Telesio (1509– 1588). Statue in the Piazza XV Marzo, Cosenza, Southern Italy, where he was born in 1509. (From ‹www.cittadeibruzi.it/ bernardino_telesio.html›)

sensed to be unpleasant.98 Thus the cerebral spirit, balancing pleasant and unpleasant sensations in a sort of felicific calculus, guides the living body along paths leading to self-preservation and away from destruction. This was also Fernel’s view, where the ultimately Aristotelian origin of the idea is more discernible. He argued that every creature seeks the pleasant and avoids the unpleasant and, he continues, “An animal sets about moving along to seek something that presents a form of a good and pleasant sort, or it turns away from something judged grim and injurious.”99

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Animal Spirit in an Age of Faith Francis Bacon (Fig. 5.15), although fully recognizing Telesio’s fresh start, would refute much of the latter’s physiological theory.100 The vast Baconian opus includes many passages on the “spirits,” so that to review them all would not be practical in the present book. Nevertheless, he often provides glimpses of educated opinion current in his time. It will be sufficient to illustrate his thoughts with just a few passages from one of his major works, the Novum organum, published in 1620. In the first passage selected, he argues that, although animate and inanimate bodies might seem quite different, their differences derive from a single factor. To quote: “the only distinction between sensitive and inanimate bodies, in those points in which they agree and sympathize, is this: in the former, animal spirit is added to the arrangement of the body, in the latter it is wanting.”101 The animal spirits, however, are easily affected by a number of inanimate agents, which are sometimes manipulated for medical purposes. This is shown in the second passage: There are two modes of condensing the spirits by soporifics or provocatives to sleep; the one by calming the motion, (p.90) the other by expelling the spirit. The violet, dried roses, lettuces, and other benign or mild remedies, by their friendly and gently cooling vapors, invite the spirits to unite, and restrain their violent and perturbed motion. Rosewater, for instance, applied to the nostrils in fainting fits, causes the resolved and relaxed spirits to recover themselves, and, as it were, cherishes them. But opiates, and the like, banish the spirits by their malignant and hostile quality. If they be applied, therefore, externally, the spirits immediately quit the part and no longer readily flow into it; but if they be taken internally, their vapor, mounting to the head, expels, in all directions, the spirits contained in the ventricles of the brain, and since these spirits retreat, but cannot escape, they consequently meet and are condensed, and are sometimes completely extinguished and suffocated; although the same opiates, when taken in moderation, by a secondary accident (the condensation which succeeds their union) strengthen the spirits, render them more robust, and check their useless and inflammatory motion, by which means they contribute not a little to the cure to diseases, and the prolongation of life.102

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Animal Spirit in an Age of Faith Both passages show that by the early 17th century the “spiritual” nature of the animal spirit was rapidly vanishing. It was well on the way to becoming just another body fluid, or humor, like blood, phlegm, or bile. Its relation with the soul, so intimate in the Scholastic thought of the medieval period, is becoming more and more questionable. We shall return to Francis Bacon in Chapter 7 but we can see here that the stage was set and the actors already learning their parts for the great revolution in natural philosophy that would usher in the early Modern period.

Concluding Remarks It was only toward the end of the 16th and beginning of the 17th centuries that serious doubt began to be cast on the age-old doctrine of animal spirit. We shall see in the next section of this book how experiments and observations in the latter part of the 17th century began to shake the theoretical foundations of the old neurophysiology. In the present chapter we have noted how difficult it was for the scholars of the Middle Ages, and even the Renaissance, to break free from the age-old theories that first emerged in Alexandria a few centuries BCE. This was largely due to the primitive state of anatomy prior to the appearance of Vesalius, in particular, in the mid-16th century. With preservative methods other than cold temperatures hardly existing,103 and with strict limitations on the number of cadavers—especially with regard to the far less frequently studied female body—available for proper inspection for most of this period throughout the Christian West, this is hardly surprising. But, in addition to these technical and legal difficulties, there were also, and equally importantly, significant cultural difficulties. One was that Galen’s doctrines had become almost like Church dogmas, with the accompanying belief that all that was important had already been established. Another was that the eyes of philosophers and natural philosophers were directed toward the things of the next world rather than those of this. Importantly, also, they had a lack of confidence in their ability to interpret this world, as compared with the interpretations provided by the great names of antiquity. The writings that had come down from classical times were read, and pondered, and commented upon, but if observation disagreed with them, then, for the most part, it was concluded that the observer must be at fault. In addition, the medieval world was understood through the largely Aristotelian philosophical theology of the great Fathers of the Roman Church, especially Albertus Magnus and Thomas Aquinas. This great system of thought governed the human understanding and determined what investigators “saw” or were prepared to “see.”

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Animal Spirit in an Age of Faith Nevertheless, as we have noted, things begin to change from the so-called “12thcentury Renaissance” onwards. As noted, historian Lynn White has documented that a slow development of the technical base of medieval civilization took place in northwestern Europe throughout this period. One does not have to be a Marxist to recognize that technology profoundly influences our understanding of how the world works. The writings of classical antiquity, often filtered through Islam, began to be questioned. Jacob Burkhardt drew attention to this change in a vivid and colorful way: In the Middle Ages both sides of human consciousness—that which was turned within us as that which was turned without—lay dreaming or half awake beneath a common veil. That veil was woven of faith, illusion, and childish presupposition, through which the world and its history were seen clad in strange hues.…In Italy this veil first melted into the air; an objective treatment of the State and all the things of this world became possible.104 Vesalius, in the mid-16th century, was one of the first anatomists to fully recognize and appreciate this momentous change. His vision of the brain is startlingly modern, even though he still pays lip service to the ancient animal spirit doctrine. Physiology, as noted above, is bound to lag behind and depend on anatomy. But in his anatomy of the brain, Vesalius is quite clear that he finds nothing mysterious in what he calls a “divine and most wonderful device.” Furthermore, in his anatomizing he observed no crucial differences (other than in size) between the ventricles or the brains of humans and those of sheep, goats, oxen, cats, apes, dogs, and even (he writes) those of certain birds.105 What is he to make of this? Perhaps surprised by observing so many anatomical similarities between thinking and non-thinking organisms, he merely writes that “whatever likelihood should arise in my mind could not be set down without damaging our most holy faith.” (p.91) This is no place to attempt an analysis of the complex of forces that lay behind the profound intellectual transformations that accompanied the rebirth of learning in the Renaissance. In 1548 Fernel writes of “The globe sailed round, the printing press replacing ten thousand scribes, paper replacing vellum, the world of letters open to all to read…The recovery of the true texts of the masterpieces of Greek wisdom; learning and the fine arts blossoming afresh after a frost of thirteen centuries.”106 Nor is it a place to examine the effects that these changes had on the “most holy faith” or the response of the Roman Church. Suffice it to say that the year 1543 witnessed the publication not only of the Fabrica but also of Nicholaus Copernicus’ De revolutionibus, two of the foundation works of the modern world. These publications, along with the turn towards observation recommended in Telesio’s 1565 De rerum natura and later in Bacon’s 1620 Novum organum, thus form appropriate landmarks with which to end this chapter, and with it this section of our book. Page 41 of 49

Animal Spirit in an Age of Faith Notes:

(1) White, 1963, gives a number of reasons for the development of labor-saving technologies in the medieval West in contrast to the dearth of such technologies in the Byzantine empire and medieval Islam. His final reason is, interestingly, that rather than machinery having satanic overtones, as Blake and the Romantics often averred, it is profoundly humane in intent. The water-powered machines of early medieval times were, he writes, “produced in part by a spiritual repugnance for subjecting anyone to drudgery” (p. 291). (2) Gross, 1998, p. 253. Posidonius’ contribution is deduced from an extant fragment by the sixth-century physician Aetius of Amida (see Frampton, 2008, p. 257). (3) Anatomia Magistri Nicolai Physici (see Corner, 1927, pp. 71–72). Latin words printed here in italics appear as normal type in the quoted source. For more about this author see below at the section in this chapter labeled “The Rebirth of Anatomy”; also Grant, 1974, pp. 727–729. (4) Nicolai uses the term “marrow” to refer to the soft matter surrounding the ventricles. (5) Ibid., p. 72. Italics ours. (6) Ibid., p. 69. (7) Ibid., p. 72. Italics ours. (8) Galen, De usu partium, Book VIII, Chapter 11 (trans. May, 1968, vol. 1, pp. 415–416). (9) Clarke and Dewhurst, 1972, p. 140. (10) Manzoni, 1998. (11) For a valuable account of this translation activity and of the major centers in which it occurred, see Haskins, 1924. (12) For accounts of Constantinus Africanus see Corner, 1927, pp. 12–14; Burnett and Jacquart, 1994. (13) Frampton, 2008, p. 329. (14) Some Spanish writers believe that Gerard was not born in Cremona but in the Spanish town of Carmona near Seville. The consensus, however, is currently against this belief. A list of Gerard’s translations is given in Grant, 1974, pp. 36– 38. (15) Haskins, 1924, p. 15. Page 42 of 49

Animal Spirit in an Age of Faith (16) Osler, 1913/2004, p. 71. (17) Ernest Renan, 1866 (p. 200), writes: “The introduction of Arabic texts divides the history of science and philosophy in the Middle Ages into two perfectly distinct periods. In the first, the human mind has to satisfy its curiosity with only the meager debris of the Roman schools.…In the second period, the science of the ancients comes back once more to the West, but this time more fully, in Arabic commentaries or the original works of Greek science for which the Romans had substituted abridgements.” (18) Grant, 1974, p. 42. (19) Albert the Great’s significance in establishing natural philosophy in medieval Europe was recognized in 1941 by Pope Pius XII, when he named him as patron saint of science. Pope Benedict XVI, in a 2010 Address to the Faithful in St. Peter’s Square, emphasized that Albert’s great achievement was (and is) to show that natural philosophy (science) and theology are not irreconcilable but are different approaches to the world we experience. (20) Albertus Magnus, On Animals, Bk. 24, Chapter I, p. 58, No. 127 (trans. Kitchell and Resnick, 1999, p. 1704). See also Finger and Piccolino, 2011. (21) See Figure 1.8. (22) The outcome of this great movement of ideas has been termed the “12thcentury Renaissance.” See Haskins, 1927. (23) Albertus Magnus, On Animals, Book 1, Tract 3, Chapter I, p. 526; also Book 12, Tract 3, Chapter 3, p. 131 (trans. Kitchell and Resnick, 1999, p. 247; p. 942). For more information on Albertian psychophysiology, see Theiss, 1997. (24) Ibid., pp. 526–527. (25) Ibid., Book 20, tr. 1, Chapter 7, p. 37 (Ibid., p. 1379). (26) Albertus Magnus, Questions, IV, 9 (trans. Resnick and Kitchell, 2008, p. 163). (27) The often-used term nucha, according to the translators here cited, refers either to “the marrowy matter of the brain itself or, more likely, the spinal cord” (Ibid., p. 126, n. 44). (28) Albertus Magnus, Questions, IV, 19 (Ibid., p. 183). Albert is probably not referring to anything we would nowadays regard as a nerve but to the narrow passage (our iter or aqueduct of Sylvius) that connects our third and fourth ventricles. (29) Ibid., 5 (Ibid., p. 157).

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Animal Spirit in an Age of Faith (30) Aristotle, History of Animals, III, 5, 515a28-33 (Barnes, vol. 1, p. 818, see also Chapter 1). (31) Albertus’ older English contemporary Alfred of Sareshel (Alfredi Anglici) (c. 820–c. 912) was well aware of Galen’s cerebrocentric neurophysiology. In De motu cordis (ed. Barach, 1878) he writes (p. 100): “cerebro virtus spiritus animali replet nervos, quorum ortus a cerebro” (freely translated here as “animal spirit within the brain also fills the nerves, which are born at the brain”). (32) Albertus, On Animals, Book 1, Tr. 2, Chapter XVIII, p. 356 (trans. Kitchell and Resnick, 1999, p. 178). (33) Albertus, Questions concerning Aristotle’s On animals, III, 7 (trans. Resnick and Kitchell, 2008, pp. 125–126). (34) See Smith, in press. (35) Thomas Aquinas, Summa Theologica, Part I, Treatise on Man, Question 91, Art. 1, Reply to Obj. 1 (trans. Shapcote/Sullivan, 1990, p. 484). (36) Ibid., Question 76, Art. 7, Reply to Obj. 1 (Ibid., p. 397). (37) Aristotle, Movement of Animals, 10, 703a4-28 (ed. Barnes, 1984, vol. 1, pp. 1094–1095). Also see Chapter 1. (38) Thomas Aquinas, Summa Theologica, Part I, Treatise on Man, Question 79, Art.4, Obj.6 (trans. Shapcote/Sullivan, 1990, p. 413). (39) Ibid., Treatise on the Angels. Question 53 (Ibid., pp. 280–284). Thomas also produced a “disputation” that amounts to a veritable supernatural history—for the term “natural history” would be clearly inadequate here—where a number of properties of spiritual creatures is discussed. See Aquinas, On Spiritual Creatures (1268/1949). (40) See Alfredi Anglici’s De motu cordis: Note 31 above. (41) Aquinas’ De motu cordis, §17 (see Larkin, 1960). This work is a letter addressed apparently to a certain Master Philip, professor of medicine in Bologna. (42) See Chapter 3. (43) Bono, 1984. It worth noting that this indefiniteness continues still into modern times and ensures that the term “spirit” remains ambiguous in public speech, facing both ways—outward towards the material world and inwards towards the immaterial world.

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Animal Spirit in an Age of Faith (44) The Church’s belief in the resurrection of the dead (see Chapter 3) provided strong theological reasons for this embargo. (45) The Anatomy of the Pig, trans. in Corner, 1927, pp. 51–53. (46) See.note 3 (47) Lindberg, 1992, pp. 332–345. (48) See O’Malley, 1964, p. 11. (49) Sarton, 1947, v. 3, p. 842. (50) A modern translation into Italian and a facsimile of Mondino’s beautifully neat handwritten text has been published by Sighinolfi, 1930. (51) Bayon, 1938, p. 449, has argued that in all probability Leonardo used Mondino’s Anathomia, since the same expressions are used and the same mistakes occur. (52) A “member” had been defined by Master Nicolai the Physician in his early-13th-century anatomy as “a part of an animal which is firm and solid, composed of similar and dissimilar structures, and assigned to some special function.” That is, a structure roughly equivalent to what we now mean by “organ” or “part.” (53) See Chapter 1. (54) For good evolutionary reasons, one of the laryngeal nerves is hooked beneath the aortic arch and the other around the right subclavian artery. (55) See Chapter 2. (56) See Frampton, 2008, pp. 386–387. (57) Singer, 1957, p. 88. (58) Bayon, 1938, p. 445. (59) Reported by Antonio de’ Beatis, secretary to Cardinal Louis of Aragon. He was assisted in his labors by Marcantonio della Torre (1471–1511), who later became Professor of Anatomy at Pavia (1506–1512). See Clark, 1958, p. 157. (60) This solution to the provenance of Leonardo’s drawings of the ventricles is suggested by anatomist Ron Philo in Clayton, 1992.

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Animal Spirit in an Age of Faith (61) In 1489 Leonardo, true to his fascination with geometrical proportion, had superimposed a square grid on a drawing of the human skull and written in the accompanying notes that the center of the grid (where he later placed the third ventricle) is where the “sensus communis” and, consequently, “the soul” is located (see Keele, 1977, p. 46). It is, however, worth noting (as Vesalius did) that Galen stated in one of his numerous books that the middle ventricle was the most important (see his Doctrines of Hippocrates and Plato). (62) For a brief compendium of Leonardo’s achievements and failures as an anatomist, see Belt, 1956, especially pp. 30–35. (63) Leonardo, c. 1504–1509 (Clark 19076v; trans. O’Malley and Saunders, 1983, plate 146, p. 338). Leonardo obviously takes here “vital spirits” for “animal spirits.” (64) Leonardo, c. 1490, notes for a large diagram of the upper spinal cord and associated peripheral nerves (Clark 19040r; ibid., Plate 155, p. 356). (65) Leonardo, c. 1487, note on a page with drawings of upper and lower human limbs in exterior views and dissected to show bones and nerves (Clark 12613v; ibid., plate 153, p. 352). (66) Ibid. (67) Leonardo, c. 1487, note on a page with assorted anatomical drawings (Clark 12613r; ibid., Plate 152, p. 350). (68) Holmes, 1993. (69) An account of Berengario’s life and medicine may be found in Prioreschi, 2007. It appears that Berengario’s real name was Jacopo Barigazzi, of which Berengario might have been a corruption. (70) Berengario da Carpi, 1522/1959. (71) Singer, 1925, p. 95, states that Berengario’s treatises are the first instances of illustrated anatomy texts. It is interesting to note that his early treatise on head wounds (1518) includes an illustration of the traditional three-ventricle scheme, which seems to have been copied from an earlier treatise by Magnus Hunt (1501). See Clarke and Dewhurst, 1972, pp. 26–27. (72) Berengario da Carpi, 1522/1959 (Lind, 1959, pp. 146–147). (73) Berengario da Carpi, Commentaria, Folio 153v (trans. Lind, 1975, p. 10). (74) Ibid., Folio 412v (Ibid.). (75) Prioreschi, 2007, p. 153. Page 46 of 49

Animal Spirit in an Age of Faith (76) Jan Stephen van Calcar (or Kalkar) was a student in Titian’s painting studio and later became a well-known painter in his own right. There is some dispute whether he or another of Titian’s students, or perhaps even Titian himself, is responsible for the 11 great woodcuts in the Fabrica. The consensus however points to Calcar, and there is no doubt he was responsible for the six plates constituting the Tabulae anatomicae. (See O’Malley, 1964, pp. 124–128; Guerra, 1969; Mayor, 1984, pp. 97–115.) (77) Vesalius, 1543, Book VII, Chapter I, p. 623 (trans. Clarke and O’Malley, 1968, p. 468). (78) Ibid., p. 623 (trans. Richardson and Carman, 2002–2009, p. 163). (79) Ibid., p. 624 (Ibid., p. 165). (80) Ibid., Book VII, Chapter VI, p. 636 (Ibid, p.198). (81) Ibid, Book IV, Chapter 1, p. 315 (Ibid., p. 159). (82) Ibid., Book VII, Chapter VI, p. 635 (Ibid., p. 197). (83) See Chapter 2. (84) Vesalius, 1543, Book VII, Chapter XII, p. 642 (trans. Richardson and Carman, 2002–2009, p. 217). It is commonly assumed that Galen arrived at the conclusion that the rete mirabile should exist in man only because his dissections were limited to animals, for had he dissected humans too he would not have found this structure. Yet Galen also dissected Barbary apes, which he believed to be the most closely related of all animals to humans (because they stand upright), and they too lack a rete mirabile. Hence, even Galen, the greatest dissector of antiquity, might have been blinded by the demands of his theory. (85) Ibid., Book VII, Chapter XII, p. 621 (Ibid., p. 159). For additional information about Vesalius’ views concerning the rete mirabile, see Bataille et al., 2007. (86) Ibid., Preface, p. iii, (Ibid., p. li). (87) See Bono, 1995, pp. 97–103. (88) Further detail in Granit, 1971. (89) A modern translation of the final 1567 version into English has been made by Forrester, 2003. Sherrington’s famous biography, published in 1946, points out (p. 81) that the ambiguous half-psychological/half-physical nature of animal spirit played a crucial role in Fernel’s psychophysiology: “It was as though matter, poured out thin, lost some of its materiality…animal spirits became, in the [brain], a thought, and the transmutation asked no comment.”

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Animal Spirit in an Age of Faith (90) See Forrester, 2003, p. 8. (91) Fernel, 1567, Book 6, Chapter 10, p. 135 (trans. Forrester, 2003, p. 467). (92) Ibid., Chapter 13, p. 142 (Ibid., pp. 489–491). (93) Ibid., Book 5, Chapter 5, p. 108 (Ibid., p. 379). Vesalius was similarly scornful, as noted in the second of the opening quotes to this chapter. This persistence of book learning over the straightforward evidence of the eyes reminds the modern reader of the Aristotelians passing beneath Pisa’s leaning tower and refusing to accept that heavy and light bodies fall to the ground at the same rate! This story is probably apocryphal and more likely, if anything, a “thought experiment.” (94) Granit, 1971, p. 585. (95) Bacon, Novum organum, Book 1, §63 (ed. 1990, p. 113). (96) Telesio, De rerum natura, Book 1, pp. 26–27; Book 5, pp. 122–123; Book 8, pp. 178–179 (Deusen, 1932, pp. 38, 53–55). (97) Ibid., Book 5, pp. 139–141 (Ibid., pp. 56–57). (98) Ibid., Book 7, pp. 2–5 (Ibid., pp. 58–59). (99) Fernel, 1567, Book 5, Chapter 9, p. 99 (trans. Forrester, 2003, p. 347–349). Cf. Chapter 1. (100) For a review of Bacon’s view of Telesio, see Deusen, 1932, pp. 13–18. (101) Bacon, Novum organum, Book 2, §27 (1990 ed., p. 157). (102) Ibid., §49, III (Ibid., pp. 190–191). (103) Criminals would not be executed in some places until the winter, so their bodies would not decompose too rapidly for proper anatomical examinations, which could take many days to complete. (104) Burckhardt, 1945, p. 81. (105) Vesalius, 1543, Book VII, Chapter 1, p. 624 (trans. Richardson and Carman, 2002–2009, p. 165). Vesalius is referring here to “the conformation of the parts [of the brain].” He is clear that the human brain is far larger, in proportion to the size of the body, than that of “any other animal” and to this fact he attributes the far greater “rational force” displayed by humans. (106) Quoted in Sherrington, 1951, p. 17.

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Introduction

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.95) Introduction Shakespeare guyed his token schoolmaster, Holofernes, as “full of forms, figures, shapes, objects, ideas, apprehensions, motions, revolutions” and went on to affirm that “these are begot in the ventricle of memory, nourished in the womb of the pia mater, and delivered upon the mellowing of occasion.” All and everything was jumbled together in his semi-educated brain. What could be believed? In the late 16th and early 17th century the old order was beginning to fall apart. In England the old religion with its profound resonances, its feast days, Latin creed, reredos screens, saints and devils, was being torn asunder. In 1536 the king ordered the monasteries to be broken up, their images destroyed, their lands forfeited. On the continent the old faith had been attacked for its florid corruption. Popular revulsion found its expression in the works and words of Luther, Zwingli, Calvin, and many others. At the beginning of the next century John Donne famously remarked that “’Tis all in pieces, all coherence gone,” and that “new philosophie calls all in doubt.” The 17th century was an age of uncertainty. In England the civil war and its religious undertones wrenched society apart. In France the insurrection known as the Fronde tore at the established order. In Italy the trial and condemnation of Galileo questioned the freedom of scientific enquiry, and nascent scientific bodies such as the Lincei, Cimento, and the Neapolitan Investiganti were persecuted and/or disbanded.

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Introduction The breakup of the old dispensation was both generated by and reflected in science. The storm had been long in coming. It broke in 1543 when, as we noted in at the end of the previous chapter, two great books were published, Vesalius’ Fabrica and Copernicus’ De revolutionibus. Of the two, the latter was the most upsetting to the established order. Copernicus took the precaution of dying before it was published. He nevertheless did not see it as prejudicial to the Catholic religion; indeed, he dedicated the book to the Pope. He regarded his work simply as a more economical way of describing the movements of the heavenly bodies than the traditional Ptolemaic system.1 Others did not see it quite that way. Instead they saw it as depicting physical reality rather than merely an improved mathematical theory. The heliocentric theory opened a breach in a central part of the medieval world-picture. Gingerich2 has shown that De revolutionibus had wide circulation. It was a major item in that “new philosophie,” which, as we saw above, John Donne felt called all in doubt. When Galileo sought to make it the basis of a new science he was sent for by the Roman Inquisition. Another who felt the breakup of the old order and sought to put together a new science was René Descartes. It can be argued that both Galileo and Descartes, far from seeking to undermine the old religion, were in fact trying to reconcile the new knowledge with the old Faith.3 Unfortunately the ecclesiastical authorities did not see it that way. It was against this background that early modern science struggled to emerge. The old order faced challenges from a thousand different directions. Nothing, however, is inevitable. The great civilization of Middle Kingdom China persisted virtually unchanged for millennia; the Mexica in central America knew nothing of the wheel. The old order might have held firm. But it was not to be. In Europe new ideas gradually gained traction. New thinking took hold progressively in astronomy and physics and then spread to other fields. Nowhere, however, was this new thinking slower to take hold than in the physiology of the brain and the doctrine of animal spirits.

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Introduction In this section we start with the highly influential work of the French philosopher and mathematician René Descartes. He attempted to show how human neurophysiology and behavior could be explained in entirely mechanistic terms. In a way he set out a position so stark that subsequent 17th-century thinkers, especially thinkers raised in a more biological or medical milieu, reacted against it. In particular his neurophysiology imagined the body’s musculature to be activated by “animal spirits” coursing down tubular nerves. His ideas had more to do with his metaphysics than with anatomical and physiological reality. Indeed they are far less realistic than the neurophysiology developed by the great anatomists and physiologists of the preceding century (see Chapter 5). The two chapters following Chapter 6 show, first, how the 17thcentury turn towards experiment and observation cast profound doubt on this notion and, second, how scientists began to develop new theories consonant with the new evidence. But the notion of animal spirit lingered on and, as we shall see in the last chapter of this section, still saturated the late-17th-century psychophysiology of Thomas Willis, the great English neuroanatomist and physician who coined the term neurology. The story of the slow decline and fall of the doctrine is complex and many-sided; it is indeed an odyssey that needs a Homer to do it justice. (p.96)

(p.97) Chronology Science

Cultural Context

1600 Gilbert: De magnete 1604 First production of Hamlet 1604 Collège Royal founded at La Flèche 1605 Bacon: Advancement of Learning 1605 Cervantes: Don Quixote 1610: Galileo: The Starry Messenger 1619 Harvey announces discovery of the circulation 1620 Bacon: Novum organum 1621 Donne Dean of St. Paul’s 1627 Harvey: De motu locali animalium 1628 Harvey: De motu cordis et sanguinis

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Introduction

Science

Cultural Context

1629–33 Descartes at work on Le Monde including L’Homme 1632 Galileo: Two Great World Systems

1632 Rembrandt: The Anatomy Lesson 1633 Trial and condemnation of Galileo

1637 Descartes: Discourse on Method 1638 Galileo: Two New Sciences 1641 Descartes: Meditations on First Philosophy

1642–9 Revolution in England

1648 van Helmont: Ortus medicinae 1648 Peace of Westphalia: end of the Thirty Year’s War 1648–53 The Fronde in France 1649 Descartes: Passions of the Soul

1649 Execution of Charles I

1649 Gassendi: Animadversiones 1651 Hobbes: Leviathan 1657 Foundation of Accademia del Cimento 1660 Foundation of Royal Society

1660 Pascal: Pensées 1660 Restoration of British monarchy (Charles II) 1660–61 Vermeer: View of Delft

1661 Boyle: Sceptical Chymist 1662/1664 Descartes: L’Homme (published posthumously) 1664 Willis: Cerebri anatome 1664 Swammerdam: frog nerve–muscle preparation 1664 Croone: De ratione motus musculorum 1665 Hooke: Micrographia

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Introduction

Science

Cultural Context

1665 Malpighi: De cerebro 1666 Foundation of Académie Royale des Sciences 1667 Stensen: Elementorum myologiae specimen

1667 Milton: Paradise Lost

1669 Malpighi: De viscerum structura exercitatio anatomica 1669 Stensen: Discours sur l’anatomie du cerveau 1672 Glisson: Tractatus de natura substantiae energetica 1672 Willis: De anima brutorum 1674 Van Leeuwenhoek: microscopical sections of optic nerve 1674 Mayow: De motu musculari et spiritibus animalibus 1677 Glisson: Tractatus de ventriculo et 1677 Spinoza: Ethics intestinalis 1677 Racine: Phaedra 1678 Lorenzini: Observationi intorno alle torpedini 1680/81 Borelli: De motu animalium 1681 Croone: 2nd edition of De ratione motus musculorum 1687 Newton: Principia 1688 “Glorious Revolution” in England 1690 Locke: Essay concerning Human Understanding 1692 Bayle: Dictionaire historique et critique 1702 Baglivi: Specimen quatuor librorum de fibra motrice et morbosa 1704 Newton: Opticks (1st edition) Page 5 of 6

Introduction Notes:

(p.98) (1) The story of the publication of de Revolutionibus is, as always, more complicated and nuanced than a brief paragraph can tell. In fact it was a letter inserted by a Lutheran theologian, Osiander, in place of Copernicus’ own preface which asserted that the book did not pretend to tell the ‘truth’ but only a simpler way to calculate the movements of the heavenly bodies. These movements were of importance to the ecclesiastical authorities in determining the date of Easter and other Church festivals and also in more mundane matters such as nautical navigation. (2) Gingerich, 2004. (3) See Gaukroger, 1997; Santillana, 1958.

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René Descartes

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

René Descartes C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0006

Abstract and Keywords This chapter discusses René Descartes, who is an essential historical figure. It studies his highly influential work, where he tried to show how human neurophysiology and behavior could be entirely explained using mechanistic terms. It shows that Descartes' neurophysiology imagined that the body's musculature would be activated by “animal spirits” that course down tubular nerves. It determines that his ideas were more related to metaphysics than with physiological and anatomical reality. This chapter also states that Descartes was the first to make all nature inanimate. Keywords:   René Descartes, human neurophysiology, inanimate, mechanistic terms, behavior, musculature, tubular nerves, metaphysics, anatomical reality

I suppose the body to be nothing but a statue or machine made of earth. René Descartes, Treatise of Man René Descartes (Fig. 6.1) is a pivotal figure in our history. Coleridge believed that he was the first to make all nature inanimate.1 In this chapter we shall see that although his neurophysiology is based firmly on the concept of animal spirits, these spirits were, in his treatment, entirely inanimate.

Descartes’ Life

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René Descartes Who, then, was he? He was born in the heart of France, in the small town of La Haye, later La Haye-Descartes, and now known simply as Descartes, deep in the Touraine, midway between Poitiers and Tours. Records show that he was baptized in the church of Saint-Georges on April 3, 1597. He was a delicate child. His mother died a few days after his birth and he was carefully nurtured by female relatives. His father, however, did not neglect him and in recognition of his son’s insatiable curiosity took to calling him his “philosopher.” Although Descartes was born in La Haye he probably spent little time there. At the tender age of 9, he was sent away to school in La Flèche. Then, in 1607 his father, with a new wife and four stepchildren, moved the family home some 20 km further south to the larger town of Châtelerault. La Flèche, the town of René’s school days, is a little over 100 km northwest of Châtelerault. Nowadays the College is a military school, the Prytanée Militaire, offering secondary education for those wishing to enter the armed forces. Its massive buildings dominate the little town (Fig. 6.2). In Descartes’ day it had just been established. It was the greatest of the Jesuit colleges, which Henri IV founded after his reconciliation with the Holy See. It was opened in January 1604 under the title of “Collège Royal Henri-le-Grand” with the mission “to select and train the best minds of the time.” The 9-year-old René arrived in April 1606. Descartes’ arrival had been postponed from January due to the delicate state of his health. He was, nevertheless, one of its foundation scholars. His biographer reports that even at 8 years old he was marked out by his curiosity and love of learning. His father entrusted him to the special care of Père Charlet, the Rector of the College, and the young René formed a friendship with his mentor that was to last the rest of his life. Father Charlet was quick to recognize René’s genius and accorded him special privileges. One that, it may be imagined, his fellow pupils envied was permission to lie abed in the morning to meditate and think. This comfortable habit René continued for the rest of his life. It is said that we owe much of Descartes’ best work to these dreamy matudinal meditations.

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René Descartes La Flèche provided the young René with the best education available at the time. He took the full traditional 8-year program: the 5-year “trivium” of the verbal arts (grammar, rhetoric, and dialectic [logic]) followed by the 3-year “quadrivium” of the mathematical arts (arithmetic, music, geometry, and astronomy), although at La Flèche metaphysics, natural philosophy, and ethics were added.2 All that was permitted to be known, all that was permitted to be conjectured, was laid before him. He came to conclude, however, that there was little difference between the two. Always he was concerned to dig deep and to discover lasting bedrock. It was only when he came to the last years of the curriculum that he was allowed to study mathematics, and it was only then that he felt he was beginning to deal with certainty. Mathematics and theology are two very different subjects, but they do have one underlying feature in common: both have to do with the immutable, the unchanging. In the early 17th century, as we noted in the introduction, the old order was disintegrating, leaving behind a turmoil of new ideas, new conjectures. Mathematics and theology seemed sheet anchors in the storm. A philosophical temperament such as Descartes possessed demands some abiding place to settle and build. Descartes’ life work was to find certainty in the world, which could compare with the calm certainty of his mentors at La Flèche. (p. 100) In 1614, at the age of 18, René left the College and returned to his father’s home, which had then removed to Brittany. After a short period at Poitiers studying law and perhaps some medicine, he left to follow in the train of the armies of the time, visiting different countries, observing manners and customs, attending ceremonies and diplomatic gatherings. He had, he writes, grown tired of study and book learning. Eventually he found himself at Neuberg and Ulm in what is now Baden-Wurttenberg. The year was 1619. It was the winter of the stove-heated room and his famous dreams. It was the year of the cogito.3

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René Descartes This is not the place to discuss Figure 6.1: René Descartes in his study. the origin or significance of the (From Wikimedia Commons, ‹http:// cogito. Suffice it to say that in serendip.brynmawr.edu/Mind/ his quest for certainty, casting Descartes.html›) aside loose earth, as he says, in order to find bedrock on which to build his philosophy, he realized that, although he could doubt everything, including, he says, the “truths” of mathematics, he could not doubt, while doubting, that doubting was occurring: “cogito ergo sum, je pense donc je suis, I think therefore I am.” It is not, however, Descartes’ metaphysics that concerns us in this book but his physiology. One result of his metaphysics is, however, worth emphasizing. In cutting mind, res cogitans, sharply off from body, res extensa, Descartes opened the way for the new science of Galileo, a science that disdained mysterious vital forces, to be applied in the study of animal and human bodies. It became possible to study the human body mechanistically. This, of course, was a dangerous thing to do in the early 17th century. Seeking peace and tranquility Descartes had migrated from France, from Paris and its disputes, to the Netherlands. “I sleep here ten hours a night,” he wrote to a friend, “with not a care to awaken me.” He spent his days constructing his great work, Le Monde. No one bothered him. In the great city of Amsterdam, where he had settled, everyone was so busy with commerce that no one noticed him: “I could live here all my life,” he writes, “without being seen by anyone.” This suited him perfectly. It could not go on. In 1633 devastating news came from Italy. Galileo had been arraigned before the Inquisition at Rome, found guilty of heresy, shown the instruments of torture, forced to retract, and sentenced to perpetual house arrest. Descartes was not only devastated but also astonished. What had Galileo done? All he had done was to publish a treatise, Dialogue on the Two Great World Systems, in which he had clearly shown that the Copernican heliocentric astronomy was superior to the Ptolemaic system. Descartes had thought the heliocentric theory was acceptable to the Church so long as it was not preached from the pulpit, just as nowadays the Darwinian theory is acceptable so long as the Biblical story is preached every Sunday.

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René Descartes Descartes was a faithful Catholic. He would, he said, not publish anything that went against the teachings of the Church. He was always avid for a quiet life. Discretion was for him by far the better part of valor. He was content to live in obscurity if this were the only way to retain his peace of mind. It was unfortunate, however, that his own opus, Le Monde, also assumed Copernicus’ heliocentric theory. So be it. He would withhold his treatise from publication. He writes to his old friend and early colleague Marin Mersenne (1588–1648) in some agony of mind that he is so astonished at the news from Italy that “I am almost resolved to burn all my papers, or at least not show them to anyone.”4 Note the “almost.” He still had hopes!

Descartes’ Neurophysiology But it was not only astronomy and optics that Descartes was working on during those anonymous years in Amsterdam. He was also fascinated by anatomy. How was the body constructed? How did it work? He was not the only man in Amsterdam fascinated by anatomy. The Amsterdam guild of surgeons was flourishing. Famously the young Rembrandt van Rijn, just starting out as a portraitist in the early 1630s, was painting one of his greatest pieces, the 1632 “Anatomy Lesson of Dr. Nicolaes Tulp” (Fig. 6.3). Here we see Dr. Tulp demonstrating the anatomy of the arm to seven members of the guild. Tulp pulls the tendons of the cadaver’s forearm (p.101) with his forceps and shows the mechanism by which they flex the fingers, copying the movement with his own raised left hand.

Descartes was never a member of the surgeons’ guild and never a professional anatomist, yet he was fascinated. In the early 1630s when he lived in Amsterdam, he took lodgings on Kalverstraat—Cow street—a street lined with butchers’ shops. He was a frequent visitor. His earliest biographer, Adrien Baillet (1649–1706), writes that in the early 1630s “his eagerness for knowledge of

Figure 6.2: Collège Royale at La Flèche in 1655.(From Wikimedia Commons, ‹commons.wikimedia.org/wiki/ File:Collège_La_Flèche_(1655)›)

the subject made him visit, almost daily, a butcher’s shop to witness the slaughter; and that he caused to be brought thence to his dwelling whichever of the animal’s organs he desired to dissect at greater leisure.”5 Although not a professional, he was no armchair theorist. Indeed, found among his papers after his death was the manuscript of a dissection manual, Excerpta anatomica. Page 5 of 19

René Descartes Such was his eagerness for anatomical knowledge that, according to Baillet, he exposed himself to ridicule and malicious gossip among his Dutch neighbors. Descartes wrote to Mersenne in December 1632 saying that he is busy “dissecting the heads of different animals in order to explain what memory and imagination consist of,”6 and in another letter to Mersenne in February 1639, he writes of how he has not only consulted Vesalius and other writers on anatomy but has also been dissecting animals for over 11 years.7 Figure 6.4 shows one of his dissections of the sheep brain. But how did the body work? In his last treatise, the 1649 Passions de l’Ame, he gives pride of place to William Harvey’s 1628 discovery of the circulation of the blood and ends by describing the movements of the muscles. These, he writes, are opposed to each other so that when one shortens the other lengthens, and vice versa (Fig. 6.5b). He ends by declaring (p.102)

Figure 6.3: “The Anatomy Lesson of Dr. Nicolaes Tulp” (Rembrandt, 1632). (From Wikimedia Commons, ‹en.wikipedia.org/ wiki/File:The_Anatomy_Lesson.jpg›)

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René Descartes that “all these movements of the muscles…depend on the nerves which resemble small filaments, or little tubes, which proceed from the brain and thus contain, like it, a certain very subtle air or wind which is called animal spirits.”8

Thus we see that, in the mid-17th century, the notion of animal spirits lives on. Descartes’ neurophysiology is built on this time-honored notion. Nicolaes Tulp may have demonstrated the mechanical action of the tendons by pulling at them with forceps, but how the muscles pulled them in the living body remained a mystery. Descartes, like Timaeus two millennia before, constructed what seemed to him the most likely explanation using the concepts and knowledge available at the time.

Figure 6.4: Sheep brain, inferior aspect. From Descartes’ Excerpta anatomica.

This “likely explanation” is found in many places in Descartes’ opus but most fully in the treatise he suppressed on learning of Galileo’s trial and condemnation. This treatise, part of the suppressed Le Monde, he called simply L’Homme (Treatise on Man). Although it was written in 1632 it was not published until 1662, 12 years after its author’s death. The 1662 Latin edition was translated into French and published 2 years later, in 1664, by La Forge.

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René Descartes It had a somewhat checkered history; indeed, it almost disappeared altogether. At the end of his life, in 1649, René accepted an invitation to tutor the young Queen Christina of Sweden (1626–1689). After some hesitation, he bundled up his papers in a cabin trunk and set off for Stockholm. It is speculated that the purport of his physiology had become known by this time, for rumor had it that a mechanical puppet lay concealed in the trunk.9 Be this as it may, when Descartes arrived in the Swedish capital in the winter of 1649, the Queen asked him to retrieve his papers from the trunk and begin collating them into treatises. She also asked him to provide tutorials before dawn in the freezing winter weather. This, as we noted above, was very far from Descartes’ taste and it proved too much. He caught a chill and died in February 1650. His papers were collected, put back in the trunk, and returned to France. Unfortunately, the boat carrying them capsized in the Seine. The trunk lay at the bottom of the river. Fortunately steps were taken to recover them, and 3 days later they were brought ashore, soaking wet, and hung on a line in the French sunshine to dry. Do we have all the papers as Descartes would have wished them to be? We cannot tell. Certainly L’Homme starts abruptly, almost in mid-sentence, as if there are some pages missing. “These men,” the Treatise begins, “will be composed, as we are, of a soul and a body.” Did earlier pages describe “these men”?10 It seems probable. In the next paragraph he writes, “I suppose the body to be nothing but a statue or machine made of earth” and goes on to point out that “we see clocks, artificial fountains, mills and other such machines.” Descartes had been greatly impressed by the water-driven automata he had seen as a young man in the grottos at St. Germain-en-Laye, just outside Paris. These had been constructed, as we noted in Chapter 4, by two Florentine brothers: Tommaso and Allessandro Francini.11 If the Francinis could construct manikins that would seemingly leap into life at the touch of a hidden spring, then why should not an omnipotent deity have constructed the human body on the same principle? Descartes thus set about explaining how it might be done. We noted above that he fully accepts Harvey’s great discovery that the blood circulates, rather than ebbs and flows as the ancients had thought. But on one central issue he differed from the Englishman. He still believed that the heart (p.103)

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René Descartes was the center and source of the body’s heat. He believed that within it is to be found “a continual heat,…a species of fire which the blood of the veins there maintains”12 as fuel does a fire. This, as we have noted in earlier chapters, is an ancient idea, and one that finally fell into desuetude only with the rise of physiological chemistry in the 19th century.

He explained his theory in detail in L’Homme. Food is digested in the stomach and intestine, absorbed into the portal veins, and carried to the liver, where it is transformed into venous blood (a process he

Figure 6.5: (A) The complex system of nerve tubes and valves that Descartes imagined could cause the integrated movements of antagonistic eye muscles. (B) Simplified figure showing how the inflation of one extrinsic eye muscle and the deflation of the other turns the

eyeball. Both figures from L’Homme compares to winemaking). The (1664). blood then passes into the right auricle of the heart via the vena cava and thence into the right ventricle. From there it circulates, as Harvey saw, via the lungs, where it is “activated,” to the left ventricle of the heart, in whose wall lurks “one of those dark fires” (un de ces feux sans lumière).13 Instead of the heart’s work being done at systole (as Harvey had shown), Descartes argued that it was done at diastole. He argued, in line with ancient tradition, that “activated” blood is particularly flammable. It is volatilized by the dark fire in the ventricular wall and expands vigorously. It is this expansion that causes the diastole of the ventricles. The volatilized blood quickly fumes off up the pulmonary artery, and the aorta and the heart collapse back to their original size. This view, which seems to us so obviously wrong, was far from seeming so incredible in the early 17th century. Descartes presents much evidence in its favor. If the thorax of an animal is opened, he writes, the heart is evidently warm to the touch. He ascribes the hardening of the ventricular walls, which Harvey correctly saw as due to contraction of cardiac muscle, to the pressure of the volatilizing blood beating against those walls. Anyone who has watched a mammalian heart beating will recognize the difficulty a 17th-century observer would have in deciding between the Harvey and the Cartesian theory.

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René Descartes Harvey, however, in being the better comparative anatomist, had spent many hours observing the slower action of the hearts of cold-blooded vertebrates. It was largely on the basis of this experience that he had arrived at the correct interpretation of the heart’s action. Descartes had not taken this approach. Descartes’ theory, too, for all his protestations about being his own man in the fields of science and philosophy, was based on the time-honored physiology of the ancients (Fig. 6.6). In particular it was based on the ancient idea that the heart was the source of the body’s heat and that the blood on being heated immediately expands and volatilizes. “The blood,” he writes, “is of such a nature that when it is heated only a little more than usual it instantly expands.”14 The notion of the blood expanding and volatilizing is central to Descartes’ physiology. It causes the blood to flow round the circulation (Descartes, like Harvey, is quite familiar with the valves of the heart and the veins that direct its flow) and, in particular, via the carotid arteries to the (p.104) brain. When the carotids reach the brain, they divide into innumerable branches, which ramify through its substance. The blood fuming up from the left ventricle will, he argues, have its most “subtle” and rarefied moiety in the van. This fraction, alone, will penetrate the labyrinthine channels of the cerebral substance. The less rarefied moiety consisting of larger particles will find its way through less intricate and narrow channels to the head and face. But the first fraction, the subtlest and most rarefied moiety, consisting, as he writes, of “les plus vives, les plus fortes et les plus subtiles parties de ce sang” will penetrate the cerebral substance itself.15 This Figure 6.6: Diagram to show the subtlest portion of the blood has a Cartesian neurophysiology. (From Smith, crucial role to play: it is destined 2004) to form the animal spirits. It “serves not only to nourish and sustain its [i.e., the brain’s] substance but principally to produce a very subtle wind (un certain vent très subtil),” or, better, “une flame très vive et très pure,” which one calls animal spirits (les esprits animaux).16

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René Descartes Thus we see that for Descartes animal spirits are thoroughly material. They have no mental aspect. It is merely the most rarefied and “subtilized” moiety of the blood. It consists of the minutest particles that just because of their minuteness can move with extreme rapidity—“like the jets of flame issuing from a torch.”17 This rarefied filtrate ultimately finds its way through the meshwork of cerebral vessels to “gland H.” This gland, customarily identified as the pineal, hangs down, according to Descartes, into the third ventricle. The “smallest and most agitated” spirits arriving in it jet out into the surrounding ventricular cavity— like a “very full-flowing spring.” The ventricles thus come to be filled with animal spirits. Nowadays we call the watery content of the ventricles cerebrospinal fluid (CSF). Animal spirits have faded into water molecules and a few molecules of other materials. We now know that the CSF has a number of functions, including buffering against mechanical shock, transmission of neuroendocrine factors, prevention of brain ischemia, etc. It seems likely that Descartes had first-hand knowledge of it from dissecting the brains of sheep obtained from the butchers’ shops in the Kalverstraat where he lived. But for Descartes animal spirits had a far more important function to perform than today’s CSF. They were responsible for communicating the brain’s commands to the muscles. They were central to his neuromuscular physiology, central to his theory of how both voluntary and involuntary behavior is controlled by the brain. To understand his theory we have to recognize, once more, that Descartes lived in the early 17th century, before microscopy had made an impact. In consequence, he was still working with the age-old physiology of hollow nerves. In Passions of the Soul he describes his concept succinctly: “there are three things to consider in nerves. First, there is the marrow, or internal substance, which extends in the form of tiny fibers from the brain, where they originate, to the extremities of the parts of the body to which they are attached. Next, there are the membranes surrounding the fibers, which are continuous with those surrounding the brain and form little tubes in which the fibers are enclosed. Finally, there are the animal spirits which, being carried by these tubes to the muscles, cause the fibers to remain…completely free.”18 As shown diagrammatically in Figure 6.7, the filaments, which are destined to play an important role in the Cartesian neurophysiology, float freely in the animal spirits with which the tubular nerve is filled. How do animal spirits cause muscular movement? Descartes’ theory makes use of the organization of muscles into antagonistic groups (see Fig. 6.5). When at rest antagonistic muscles contain a balanced quantity of animal spirits. When, however, the tubular nerve innervating one muscle delivers an extra spurt of spirits, the balance is upset. A snowball or avalanche effect follows. The extra quantity of spirits in one muscle opens valves, which allow spirits to flow across from the other. Thus as one muscle balloons, which for Descartes implies contraction, the other deflates (i.e., relaxes and lengthens).19 Thus the joint is moved. Page 11 of 19

René Descartes But how does the brain determine which muscles to activate? There are two cases: involuntary (reflex) movement and voluntary (willed) movement. (p.105) Descartes was one of the first to provide a neurophysiological scheme for reflex movement. It is in this scheme that the significance of the central thread floating in neuronal animal spirits becomes clear. These threads are required to transmit information from the body’s surface to the brain. They play a fundamental role in Cartesian sensory

Figure 6.7: Descartes’ concept of a tubular nerve fiber. The fiber is filled with animal spirits in which floats a slender filament. When the filament is pulled (b) it opens a valve in the spirit-filled ventricle and these, being under some

physiology.20 Descartes maintains that when a sense organ or any part of the body is stimulated, these intra-neuronal filaments are pulled like the bell-pulls hydrostatic pressure, flow out along the connecting the servants’ quarters tubular fiber. of great houses to the rooms above. The cerebral ends of the filaments are attached not to bells but to valves in the walls of the ventricle and, when the string is pulled, the valves open and animal spirits flow out along the tubular nerve to the appropriate muscle. This is the Cartesian reflex. He gives several examples.

First he describes the blink reflex when a friend jokingly shakes his fist before our eyes. The ensuing blink, he points out, is certainly not willed. Indeed, it is difficult if not impossible to will the eyes to remain open. Descartes explains the reflex by arguing that the raised fist affects the retina in such a way that the filaments in the optic neurons are pulled and that this leads to the opening of the ventricular cocks leading into the nerves running to the muscles responsible for the blink.21 He does not explain, however, the precise way in which the pulling of the cords in the optic neurons that open valves in the walls of the ventricle is linked to the opening of valves leading into the neural tubes running to appropriate muscles. The second and more famous example that Descartes provides is illustrated in Figure 6.8. This figure, reproduced from L’Homme, illustrates the mechanism responsible for the reflex withdrawal of the foot from a flame. The particles of flame beat upon the flesh of the foot, causing the slender intra-neural filament (c—c—c-) to open a valve (de) in the cerebral ventricle (F). This allows animal spirits in the ventricle to escape and flow “some to muscles which serve to pull the foot away from the fire, some to muscles which turn the eyes and head to look at it, and some to muscles which make the hands move and the whole body turn in order to

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René Descartes prevent it.”22 Again, he does not explain how the connection between input and output is made in the brain.

Finally, in a third example, he does sketch a mechanism by which an input signal and the output response might be connected in the cerebrum. This is shown in Figure 6.9, also from L’Homme. He gives a very unconvincing explanation of how a movement of the arm from point C to point B on the arrow could occur automatically. He says that a visual stimulus due to rays from point B on the arrow affect the retina so that the filaments in the appropriate optic nerve fibers open valves in the ventricular wall. This allows animal (p.106) spirits, which are under high pressure in the ventricle, to escape and the gland H swings so that point “b” (rather than point “c”) is opposite neuronal ending “8.”23 Animal spirits cascading out of the gland will now be directed to the neuronal tubes leading to the biceps rather than the triceps. The arm will move accordingly.

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Figure 6.8: Reflex withdrawal of foot from flame, according to Descartes’ L’Homme.

René Descartes Thus, writes Descartes, “When Figure 6.9: Reflex movement of the arm. people take a fall and stick out The eye looks at point B on the arrow and their hands so as to protect the mechanism ensures that animal their head, it is not reason spirits flow down appropriate nerves to which instructs them to do this; inflate the biceps and consequently it is simply that the sight of the deflate the triceps. Explanation in text. impending fall reaches the From L’Homme. brain and sends the animal spirits into the nerves in the manner necessary to produce this movement even without any mental volition, just as it would be produced in a machine.” Thus, he goes on, it is not incredible that “light reflected from the body of a wolf onto the eyes of a sheep should be equally capable of arousing movements of flight.”24 Descartes extends his discussion of reflex action to include visceral reflexes where the sensory surfaces and effector muscles are internal. He also gives one of the first examples of conditioned reflexes. Descartes is known to have kept a dog—Monsieur Grat (or scratch). In 1630 he writes to Mersenne that, if a dog is whipped six or eight times to the sound of a violin, it will ever after cower and whimper when it hears a violin played.25 He does not say whether he tried different tunes. Nevertheless, poor Monsieur Grat!

So much for Descartes’ neurophysiology of involuntary (reflex) movement. Let us turn to his equally mechanistic theory of voluntary movement. Here we return to his schematic gland, which, in L’Homme, he always calls simply “le petit glande, H.” According to Descartes, the gland hangs down into the ventricular cavity.26 Figure 6.10 shows that it is suspended by a delicate stalk and is, he says, largely borne (p.107) up by the animal spirits, just as a balloon is borne up by the fumes rising from a smoldering fire.

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René Descartes Animal spirits, as we have seen, Figure 6.10: In these figures drawn by jet continually from all over van Gutschoven (G), “gland H” hangs (or gland H into the ventricle. They floats) in the center of the ventricle until, never, he says, “stop for a due to slight variations in the pressure of moment in one place.” Other the spirits, it moves one way or another. animal spirits, under less The spirits pouring from the gland are pressure, pour into the ventricle represented rather like candle flames from the arteries “which carpet springing from the gland’s lower surface. the cavities of the brain.” They From L’Homme. fill out the cerebral ventricle so that it strains outward “as if it were a sail.” On death the ventricles immediately collapse and become “very narrow and almost closed.” This is what Descartes must have seen in the brains he dissected in his lodgings on the Kalverstraat. So long as the outflow of animal spirits from the gland H is symmetrical, it floats symmetrically in the center of the ventricular cavity. But the slightest inequality in the escape of the spirits will swing the gland one way or the other, out of the midline. This, in turn, affects the arteries, which carry the spirits up the stalk. There is, as in the case of antagonistic muscles, a positive feedback. The vessels, he says, are twisted one way or the other and the spirits consequently leave mostly from one or other side of the gland. This leads to increased pressure on the tubes on one or the other side of the cerebral ventricle. The tubes, as we have seen, lead out to skeletal muscles, and increased flows of animal spirits along their lengths lead to the movement of a particular limb or other bodily part.2728 Once again the precise way in which the jets of animal spirits are directed to a precise set of tubes and hence actuate a precise set of muscles is not described. Descartes merely wants to give a general theory—a first rough scheme of how the neuromuscular system works. But, says Descartes, note one important point: the first cause of voluntary bodily movement is a tiny movement of gland H, and this movement, to cut a long story short, is caused by the “will.” Just how Descartes’ immaterial will, res cogitans, manages to sway the material gland, res extensa, is a problem for which he provides no answer. Fortunately we need not, in this book, concern ourselves further with this deep problem, a problem that in today’s parlance is called simply “the hard problem.”

Concluding Remarks

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René Descartes Thus, in conclusion, we can see that Coleridge was justified in believing that Descartes was the first to make all nature inanimate. His neurophysiology treats humans and infrahuman animals as, to quote once again the first lines of L’Homme, “earthen machines.” How the immaterial mind, consciousness in our terms, is attached to the machine remains a mystery and one that, fortunately, need not delay us in this book. Descartes’ “earthen machine” operates very much like the automata at which he had marveled in his youth at St. Germainen-Laye. Substitute animal spirits for water molecules and the two are, in principle, not greatly different. It is not surprising, therefore, to find Thomas Huxley, in the late 19th century, writing that “Descartes did for the physiology of motion and sensation that which Harvey had done for the circulation of the blood, and opened up the road to the mechanical theory of these processes, which has been followed by all his successors.”27 We can also see that Descartes’ physiology is almost entirely theoretical. Although, as we noted, he was not averse to dissection, and the distasteful business of anatomy, he was no Vesalius. The diagrams that we find in his anatomical works are mostly entirely schematic. Perhaps we should not be too hard on him: L’Homme, as we noted, was retrieved from the bottom of the Seine and all but two of its many diagrams were drawn after his death by other hands: La Forge and van Gustchoven.28 But, somewhat paradoxically, we can see in Descartes’ theory of human neurophysiology both one of the last times nerves were regarded as hollow tubes along which a subtle fluid—formed of animal spirits—flowed, and one of the first times that animal spirits were taken to be entirely inanimate. It has been said that Isaac Newton, in addition to being the first modern-era physicist, was also the last of the alchemists; similarly, Descartes might be regarded as the first modern-era neurophysiologist and also the last of the Alexandrians. He, too, looked to the future but had not entirely extracted himself from the past. Unlike Newton, however, who remarked that he disdained hypotheses (hypotheses non fingo), Descartes was first of all a philosopher and his neurophysiology was deeply hypothetical: the construct of a system-builder using and refashioning the concepts that he found in the culture of his time. Like Plato two millennia before, he sought to provide what seemed to him the most likely account of that mystery of mysteries: the workings of the human body and brain. (p.108) Notes:

(1) In the Philosophical Lectures, which Coleridge delivered in the winter of 1818–19, he says (among many other things) that “Descartes was the first man who made Nature utterly lifeless…and considered it as a subject for purely mechanical laws.” See Kathleen Coburn, 1949, pp. 376–8. (2) Details of the syllabus at La Flèche are given by Rochementeix, 1899, vol. 4.

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René Descartes (3) In the autobiographical sections at the beginning of the Discourse on Method Descartes writes that, although 1619 marks the beginning of his philosophical quest, he did not arrive at his famous formulation, cogito ergo sum, until the early 1620s. (4) Letter to Mersenne, November 1633. Mersenne won a scholarship to La Flèche in 1604, so he was an older colleague of Descartes at the College. He joined the Order of Minims and maintained a vast correspondence with most of the luminaries of the first part of the 17th century. He was not only a master of many languages but also knowledgeable about most areas of scientific research. He was Descartes’ principal correspondent and mentor. (5) Baillet, 1691. (6) Adam and Tannery, vol. 1, p. 263. (7) Adam and Tannery, vol. 2, p. 525. (8) Passions de l’Ame, Part 1, VII. In Adam and Tannery, vol. XI, p. 332. There is no reason to doubt that Descartes had read the Fabrica; yet, as we saw in Chapter 5, Vesalius is quite explicit about the lack of a cavity in (at least) the optic nerve. In book IV (p. 324) he writes, for instance, “I can assert that I never found any passage…though I dissected the optic nerves of live dogs and other large animals for this purpose and the head of a man as yet warm and scarcely a quarter hour after his decapitation. I inspected the nerves carefully, treating them with warm water, but was unable to find a passage of this sort in the whole course of the nerve…even though there ought to have been according to Galen’s opinion.” (9) This rumor had wide currency in the 19th and early 20th century. In some dramatic versions the captain of a ship in which Descartes was traveling broke into his cabin while the philosopher was asleep and opened the trunk. He was horrified to find the living/mechanical doll and with a great struggle managed to wrestle it out of the cabin and over the side. Gaukroger (1995) has been unable to find any version of the fantasy earlier than the 18th century. But the rumor does indicate the image that Descartes and his philosophy left in the years after his death in 1650. (10) Descartes, 1664, p. 1. In Adam and Tannery, Vol. XI, p. 120. An English translation can be found in Hall, 1972.

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René Descartes (11) The Francini brothers were invited from Florence by Henri IV in 1597 to construct remarkable water-driven automata in the grottoes of his newly built Chateau at St.-Germain-en-Laye, just outside Paris. The automata would still have been operational, and inspirational, when the young Descartes lived in Paris during the 1620s but, because they required expert and continuous attention, ultimately fell into complete disrepair and ruin. (12) Descartes, 1649 §VIII. In Adam and Tannery, vol. XI, p. 333. (13) Descartes, 1664. In Adam and Tannery, vol. XI, p. 123. (14) Descartes, 1648, §II. In Adam and Tannery, vol. XI, p. 231. (15) Descartes, 1664. In Adam and Tannery, vol. XI, p. 128. (16) Ibid, p. 129. For more on Descartes’ “animal spirits,” especially in relation to his theory of the memory process, see Sutton, 1998. (17) Descartes, 1649, Part 1, §10. We are aware in this neurophysiology (and in Fig. 6.6) of the continuing influence of the Erasistratean, Galenical, physiology, which had held sway for nearly two millennia. (18) Ibid, Part 1, §XII. (19) Ibid., Part 1, XI. It is interesting that Descartes places such emphasis on valves throughout his neurophysiology (see Fig. 6.5). No doubt this derives from his technological models—water-powered automata and wind-powered organs— but there may be an influence from William Harvey, whose cardiovascular physiology is based on cardiac and venous valves and which, as we saw, Descartes fully accepted. (20) Descartes departs from the traditional view (to be found in Galen) that sensory and motor nerves are different, the former being “soft” and the latter “hard.” (21) Descartes, 1649: Part 1, §XIII. (22) Descartes, 1664. In Adam and Tannery, vol. XI, p. 142. (23) The figure is drawn as if an influence from the ventricular ends of the optic nerve fibers pushed the gland back. This cannot have been Descartes’ intention. We have to remember that the figures were drawn some years after his death by his editors, La Forge and van Gutshoven.

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René Descartes (24) Cottingham, Stoothof, Murdoch, 1985, p. 161. Descartes is responding to a set of objections to his Meditations on First Philosophy sent in by the philosopher and theologian Antoine Arnauld (1616–1698). Arnauld expresses incredulity at Descartes’ mechanistic psychophysiology: “For at first sight it seems incredible that it can come about…that the light reflected from the body of a wolf on to the eyes of a sheep…should spread the animal spirits throughout the nerves in the manner necessary to precipitate the sheep’s flight.” (Ibid., p. 144). Arnauld may be remembering Albert the Great’s example that we discussed when considering his ventricular psychology in Chapter 5. (25) Letter to Mersenne, Nov. 18, 1630. Quoted in Watson, 2002, p.168. (26) There is some mystery about Descartes’ “pineal.” His drawings, which, as we noted above (note 23), were mostly done some years after Descartes’ death by his editors, show it hanging down into the ventricle. Descartes must have known from his reading of Vesalius, Caspar Bauhin, and others, as well as from his own dissections, that this is anatomically quite incorrect. For discussion see Finger, 1995; Smith, 1998. (27) Huxley, 1898. (28) See Smith, 1998.

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Experiment and Observation

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Experiment and Observation C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0007

Abstract and Keywords This chapter discusses five individuals who questioned nature instead of the books of men. The first sections discuss William Harvey and Jan Swammerdam, who are known for their works on the cardiovascular system and dissection, respectively. This is followed by a discussion on Marcello Malpighi, who researched extensively on brain structure, and Antoni van Leeuwenhoek, who provided the first authentic image of the nervous system. It ends with a section on Niels Stensen, who focused on the muscles. This chapter also briefly discusses microscopy, one of the greatest developments during the 17th century. Keywords:   William Harvey, Jan Swammerdam, cardiovascular system, dissection, Marcello Malpighi, brain structure, Antoni van Leeuwenhoek, nervous system, Niels Stensen, microscopy

I prefer a Leeuwenhoek who tells me what he sees to a Cartesian who tells me what he thinks. Leibniz: Letter to Huyghens, February 1691

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Experiment and Observation We saw in Chapter 6 that, in 1649, almost exactly halfway through the 17th century, René Descartes received an invitation from Queen Christina to visit Stockholm and tutor her in philosophy. Although he felt no great desire to expose his 50-year-old frame to, as he wrote, the “land of ice and bears,” he finally set out that autumn. He arrived in Stockholm at the beginning of October and after a couple of interviews with the Queen was dismissed to follow his own devices. Later, however, in the coldest and darkest part of one of the coldest winters on record, he was required to present himself in the Queen’s library to give tutorials once a week at 5 in the morning. This proved too much. In February he caught a chill, which proved fatal, and on the 5th, early in the morning, he died. We also saw in Chapter 6 that his effects were shipped back to France and in a final tragedy almost lost at the bottom of the Seine. However, he had published sufficient during his life to establish him, in many eyes, as the fountainhead of both modern philosophy and modern neurophysiology. His influence has been immense. Nevertheless, as we suggested in the previous chapter, although he may be regarded as standing at the beginning of modern neurophysiology, the crucial role he assigned to “animal spirits” flowing along hollow nerve tubes means he can also be regarded as standing at the end of the long tradition of Scholastic natural philosophy. He looked backward as well as forward, Januslike, a truly transitional figure. Moreover, like the Scholastics, he was intent on constructing an overarching system in which everything had its place, from the movements of the planets to the working of the brain and the human soul.1 On the other side of the Channel his slightly older contemporary, Francis Bacon (1561–1626), had, in contrast, made a decisive break with Scholasticism. He insisted that science was a progressive, cumulative endeavor, should be built laboriously from the ground up (rather than top down), should focus on the book of nature rather than the books of men, and should, moreover, be directed toward practical, useful application. He characterized the efforts of the Schoolmen as the work of spiders endlessly spinning webs to catch persons of common sense and, in another place, he calls them “cymini sectores”—“hair splitters.”2 In The Advancement of Learning (1605) he goes further. “This kind of degenerate learning,” he writes,

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Experiment and Observation did chiefly reign among the schoolmen: who having sharp and strong wits, and an abundance of leisure, and small variety of reading, but their wits, being shut up in the cells of a few authors (chiefly Aristotle, their dictator) as their persons were shut up in the cells of monasteries and colleges, and knowing little history, either of nature or time, did out of no great quantity of matter and infinite agitation of wit spin out unto us those laborious webs of learning which are extant in their books. For the wit and mind of man, if it work upon matter, which is the contemplation of the creatures of God, worketh according to the stuff and is limited thereby; but if it work upon itself, as the spider worketh his web, then it is endless, and brings forth indeed cobwebs of learning, admirable for the fineness of threads and work, but of no substance or profit.3 Bacon should probably be better regarded as the “buccinator” or “herald” of modern science rather than, as some have styled him, its “instaurator.” The latter title comes from one of his books, The Great Instauration (1620), in which he sought to lay the foundations of a modern inductive science. As against the endless disputations of the Scholastics, the bringing forward of argument and authority to be met by counter-argument and counter-authority, Bacon asked that men should turn their attention to common things. He remarks that “the hidden rock whereupon…many barks of knowledge have been cast away…(is) that men have despised to be conversant in ordinary and common matters.”4 (p. 110) Bacon’s call for a community of post-Scholastic researchers5 was answered some years after his death by the formation of the Royal Society in 1660 with its motto: Nullius in verba (nothing by words alone) and, as Sprat writes in his history of the Society, “preferring the language of Artizans, Countrymen and Merchants, before that of Wits, or Scholars.”6 But Bacon’s method is only half what modern science required. In addition to Baconian lists of what existed, of what was there, vital though these were (and are), science also required the interrogatory stance. It required that nature rather than the books of men should be put to the question. In this chapter we shall look at some of the investigators who took this advice, in particular William Harvey, Jan Swammerdam, Marcello Malpighi, Antoni van Leeuwenhoek, and Niels Stensen.

William Harvey (1578–1657) William Harvey was born in 1578 near Folkestone in Kent, the son of a prosperous mercantile family, and was educated first at the Kings School in Canterbury and then at Cambridge. From Cambridge he went to Padua, the most famous medical center at that time, to complete his medical education. He studied under Fabricius ab Aquapendente, the foremost anatomist of the age, and graduated in 1602. It is worth noting that Fabricius must at that time have been working on the valves of the veins, for he published a comprehensive treatise on this subject in 1603.7 Fabricius was Page 3 of 39

Experiment and Observation also deeply interested in embryology, carefully observing the development of the chick egg, and publishing works on embryology in 1600 and 1612. Harvey returned to England in 1602. He was a small dark-eyed man with an explosive temper (Fig. 7.1). He practiced in London and, largely due to a brilliant marriage, became physician to several eminent figures, including Francis Bacon and successively King James 1 (1618–1625) and Charles 1 (1625–1649). Aubrey tells of how he sat under a hedge during the decisive Civil War battle at Edgehill with the Prince and the Duke of York and read to them from a pocket book until “a Bullet of a great Gun grazed the ground neare him which made him remove his station.” He died in London in 1657; Aubrey says a “Palsey” gave “him an easy Passeport.”8

Figure 7.1: William Harvey by Cornelius Janssen in the Royal College of Physicians, London. (‹www.archive.org/ stream/

portraitsofdrwil100royarich#page/22/ The young Harvey was mode2up›) evidently profoundly influenced by his Paduan experience. His great work on the cardiovascular system was based on an understanding of the significance of the valves in the veins and heart and, later, he spent much time studying embryology. Aubrey remembers him at Oxford in the early 1640s coming “severall times to Trinity College to George Bathurst, B.D., who had a Hen to hatch Egges in his chamber, which they dayly opened to discerne the progress and way of Generation.”9 He also followed Fabricius in his expertise at anatomy and in broadening his anatomizing from humans to include many of the lower vertebrates. In addition to his work with the scalpel, Harvey was also a great experimentalist. But more than all this, Harvey was a thinker. Aubrey, who knew him well in his later years, says that he was “always very contemplative” and that when he lived in London was “wont to contemplate on the Leads of the house and had his several stations, in regard of the sun and the wind.” He liked, above all, to meditate in the dark and had caves dug at his residence in Surrey for this purpose.10

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Experiment and Observation Harvey’s thought differs fundamentally from that of Descartes. Unlike Descartes, the mathematician and philosopher, Harvey was fundamentally a biologist. Indeed, in many respects, he was less revolutionary than the Frenchman. His thought is hardly touched by the mechanizing impulse that stirred Descartes. His great discovery was sparked by meditating on the function of the venous valves. It may be that, like Descartes, he had been influenced by the hydraulic technology of the times. But, unlike Descartes, it set him musing on the purpose of the valves he found in his anatomizing. This is, of course, a very Aristotelian attitude of mind. Harvey, like Aristotle, was convinced that “nature” “does nothing in vain.”11 Robert Boyle reports Harvey remarking that one of the observations pointing him to his (p.111) discovery was the recognition that, as he puts it, “so provident a cause as nature (had) not placed so many (venous) valves without design.”12 He was also Aristotelian in his belief that the heart was the center of the body’s physiology. Like Aristotle he had observed that the beating heart was the first organ discernible in the chick embryo. He was also strongly influenced by classic and medieval ideas of the perfection of circles and circular motion—again a thoroughly Aristotelian concept.13 Thus in the eighth chapter of De motu cordis, where he introduces the circulation of the blood with the famous phrase, “I began to think whether there might not be a motion, as it were in a circle,” he has much to say about circles. Harvey’s musings still had a deeply medieval character. But he was also, as emphasized above, an experimentalist. He had experimental evidence for circular movement. He had estimated the quantity of blood pumped from the heart in unit time. He calculated that in humans it was about 60 mL/beat or about 57 gallons/hour. This was more than three times the weight of an average man! It was impossible that such a quantity could be supplied by the liver, as the ancient theory taught; the blood must circulate. But what of the spirit, which was alleged to be carried in the blood? Here Harvey once more showed his affinity with Aristotle. Aristotle had argued, as we saw in Chapter 1, that an eye removed from the body was no longer an eye; it was no more an eye than the eye of a statue. To be called an eye it needs must function as an eye. Similarly, for Harvey, blood outside the veins and arteries was no longer blood but “the equivocal gore.” “In their different ways,” he writes, “blood and spirit, like a generous wine and its bouquet, mean one and the same thing. For as wine with all its bouquet gone is no longer wine but a flat vinegary fluid, so also is blood without spirit no longer blood but the equivocal gore. As a stone hand or a hand that is dead is no longer a hand, so blood without the spirit of life is no longer blood.”14 Spirit, he insisted, is “no more separate from blood than is a flame from its inflammable vapor.”15

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Experiment and Observation Spirits are thus, for Harvey, not entities “superadded” to the organism but, as for Aristotle, an inbuilt feature of living matter itself. We can, perhaps, imagine Harvey in his nocturnal meditations feeling his way to this post-medieval understanding. Harvey does not, of course, propose a full-blown panpsychism. Like Aristotle, again, he sees the realms of the inorganic and the animate as separate and unconnected. He is content to accept that, as Bishop Butler (1692– 1752) was later to say, “Everything is what it is, and not another thing.” “With regard to spirits,” he writes in an essay to Jean Riolan, “there are many and opposing views…smatterers, not knowing what causes to assign to a happening, promptly say the spirits are responsible…. And like bad poets, they call this deus ex machina on to their stage to explain their plot and catastrophe.”16 But does Harvey have anything to say about, specifically, animal spirits? In the early 1620s, when he was at the height of his powers, he made extensive notes on animal motion. It was thought that these notes had disappeared or been destroyed by the Parliamentarians during the Civil War. Aubrey reports that it was one of Harvey’s most bitter sorrows that his papers had been lost during that upheaval. However, it turns out that this was not the case; his animal motion notes were not destroyed and they have been recovered, edited, and translated by Gweneth Whitteridge.17 These notes, in Latin, were composed when the passions underlying the disaster of the Civil War were gathering but had not yet broken through into armed conflict. Harvey collected them in 1627 to form a treatise De motu locali animalium. De motu is thoroughly Aristotelian in character. Indeed, Harvey refers to the Stagirite as his “Master.” The work seems strange and backward-looking to a modern reader. Many sections are devoted to discussing the correct terminology and reviewing the writings of earlier savants. Other sections and whole chapters are concerned with discussions of different types of animal motion—Harvey was always a comparative anatomist—and of how the limbs move to generate these movements. Yet others rehearse what seems obvious to us latter-day readers: that the body is moved by its appendages, that these are moved by tendons, that these, in turn, are moved by muscles. It is salutary to be reminded of how far neuromuscular physiology has come. In Harvey’s time, in the early 1620s, the distinction between sinews and nerves and muscles and “flesh” was still a matter of contention. Indeed, Harvey quotes Fabricius as teaching that it is the tendon that is the “principal instrument of contraction,” not the fleshy part or belly, for, he continues, the latter “cannot lift a limb being itself exceedingly weak.”18 It was not until the microscopy of the middle and second half of the century (see below) that the structural basis of the neuromuscular system began to become clear.

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Experiment and Observation Towards the end of the treatise Harvey begins to sketch a physiology to go along with the anatomy. It is a surprisingly Aristotelian physiology. Motive force is provided by change of quality, from soft to hard and vice versa, from moist to dry, from hot to cold. “Spirit,” he writes, “like air is in the greatest degree capable of alteration as a result of changes in temperature or appetite.” He continues with a set of further questions. Does the spirit flow through the nerves to the muscles? Is it like nutriment continuously and uninterruptedly flowing? Is the muscle movement due to “filling up”? By “ebullition”? Harvey leaves these and many other questions open. They are for future researchers to decide.19 Harvey, as might be expected from one who made the great physiological discovery of the age, the circulation of the blood and the true function of the heart, agrees with his “Master” that the heart lies “at the center.” He holds to the Aristotelian position that it is the heart that feels the sensations of “anger, fear etc. and every emotional state.” (p.112) The brain remains, for Harvey, no more than a junction box, but a very important junction box. If the nerves running from it to the body’s musculature are cut or compressed, the appendage becomes numb and/or movement is lost. But it takes its orders from the heart. Emotions set it in action. “The brain,” he concludes, is like “the mester del choro,” the choirmaster.20 It organizes, as we now believe the cerebellum organizes, the motor outflow. The nerves running out to the muscles are, moreover, “like pipes and not like reins.”21 In other words he still, although tentatively, holds the view that the nerves are hollow tubes along which the animal spirit flows. Harvey never published De motu. It strikes the modern reader as derivative and unfinished. Harvey struggles to fit his observations on nerves and muscles into the medieval framework. His treatise ends with a cascade of questions and possible analogies. He is uncertain whether to take the Galenical view that the brain is the master organ or the contrary, Aristotelian, view that the heart has the place of honor. “Is the brain the general,” he asks, “the ruler of the senate, the choir master, the architect, the master, the prime mover?” Or is it on balance, as he still prefers to think, the heart that plays this central role: “the general or ruler (the brain, the judge, sergeant major…), the musician or architect (the brain, the choir master or surveyor); the captain, prime mover (the brain, the master of the ship etc.)”22 Harvey is puzzled. The neuromuscular system did not provide opportunity for the fruitful analogies with pumps, water flows, and valves, which he had seized in his interpretation of the cardiovascular system. Much research in many areas of biology and in science in general had to be done, new and undreamt-of analogies had to become available, before the neuromuscular system, especially the brain, would begin to yield its secrets to the experimental approaches at which he was so adept.

Jan Swammerdam (1637–1680)

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Experiment and Observation If William Harvey found himself caught up in the politico-religious passions of the English 17th century (sheltering under a hedge while the battle raged all around), Jan Swammerdam was not so much caught up as torn asunder by theological conflict. Whereas Harvey viewed the battle from outside, surviving the execution of his patient, the King, in 1649, to live happily on for nearly a further decade, Swammerdam was convinced by the French mystic, Antoinette Bourignon, to give up his great work as a worthless endeavor and to die in penury. Jan Swammerdam was born in February 1637, the year that Descartes published his best-known work: the Discourse on Method. His father was an Amsterdam apothecary and also a great collector. Boerhaave (1668–1738), whose biography of Jan is the best source for his life, writes that his father’s house was “full of animals, insects especially, vegetables, and fossils…everything being disposed in its proper place and order.”23 Indeed, it became one of the sights of Amsterdam, so that citizens and visiting princes came to admire it. When Jan’s father was asked to value his collection, he replied, “60,000 Dutch florins,” but found no takers. After his death the collection was split up and sold for less than a tenth of that price.

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Experiment and Observation Jan’s father intended him for the Church and set him to learn classical languages. Jan, however, rebelled and convinced his father that his true vocation was that of a naturalist and physician. His father, consequently, took the opportunity of employing his son in cleaning and ordering his vast collection. This experience undoubtedly reinforced Jan’s enthusiasm for natural history. In 1651 the young Jan went up to Leiden, already one of the preeminent medical colleges, to study medicine and became increasingly interested in anatomy. He also met Niels Stensen (1638–1686), with whom he formed a friendship that would last the rest of his life. He met and impressed many other anatomists at this time, including Franciscus Sylvius (1614–1672), whom he impressed by his “extraordinary skill in dissecting frogs.” After his medical training in Leiden, Swammerdam traveled to France, continuing his anatomical researches, and met, among others, an individual who became his lifelong friend and supporter, Melchisédec Thévenot (1620–1692), formerly the French ambassador in Genoa. He then returned to Leiden and Amsterdam, where his father still lived. His father, however, was becoming more than a little exasperated with his son and his activities. Jan, now over 30 years old, was still being supported by him and was making no effort towards gainful employment as a physician. The elder Swammerdam grew more and more incensed at what seemed his son’s unworldliness and eventually cut off his allowance of both money and clothes. Thévenot, on learning of this contretemps, wrote offering to provide all necessary support if Jan would come to France to continue his researches. This seems to have infuriated the father even more and he forbade his son this opportunity. To placate his father Jan stayed in Amsterdam and arranged his great collection, making an accurate catalog, and afterwards continuing with his own researches. The younger Swammerdam was evidently a determined, if not obsessive, individual. We can gain an inkling of the depth of this obsession with natural history and anatomy throughout the great collection of papers, which eventually saw the light of day in 1737 as Biblia naturae (The Book of Nature).24 There we read, for instance, in the introduction to the section headed Treatise on Bees, that “some creatures…present the invisible God to our contemplation more plainly than others, as will appear from the subsequent treatise. Since, therefore, the most wise and great God has been graciously pleased to bless and crown my indefatigable and assiduous labors with some degree of success, I hope that his infinite power and immense wisdom, as well as our own weakness, will be thereby made clearer than the light at noon.”25 There are similar remarks throughout the Book of Nature.

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Experiment and Observation Swammerdam, in his indefatigable researches, dissecting minute insects under a single-lens microscope, using the light of the midday sun to see the intricacies of their anatomy, (p.113) with the sweat, in consequence, as he says, “pouring down his face,” believed himself to be seeing for the first time the true work of the great architect of all things. Perhaps his father had not been so misguided in his attempt to direct the young Jan toward the Church! But it was about this time, when he had become intoxicated by the seemingly supernatural intricacies of the anatomy and life of bees, that he came across and began to read “some of the books which the then famous Antoinette Bourignon had a little before published.”26 He contacted her and she replied, advising him to turn his attention from the works of God to the contemplation of God himself: “from the works of time to those of eternity.”27 Boerhaave puts Jan’s agony of mind this way: “On the one hand his genius urged him to examine the miracles of the great Creator in his natural productions, whilst on the other, that same allperfect Being deeply rooted in his heart, struggled hard to persuade him that God alone, and not his creatures, was worthy of respect.”28 This was the tragedy of Swammerdam’s life. Antoinette Bourignon convinced him that the work to which he had devoted his life concerned only the image of the Divine, not the Divine itself; that his indefatigable labors had been misdirected, insofar as they sought an understanding of the handiwork rather than devotion to the Creator of that handiwork; that life was short and that, while it lasted, its focus should be on the “immortal God” himself, not on his works in this fallen world. Swammerdam, accordingly, finished his work on bees, gave it away, and on Bourignon’s advice, “withdrew himself entirely from all converse with the world” and came ultimately to “utterly detest as vain and insignificant the things which he formerly most delighted in.”29 From this point his life deteriorated. He suffered from quartan and tertian malaria, which sapped his strength. He would in no way listen to the entreaties of his friends and physicians and for months stayed silent in his chambers. He had no money or any possessions, save his collection. Ultimately he was forced to arrange its sale in single lots, despite knowing that this would greatly diminish its value. It finally sold for less than a tenth of his father’s valuation. He arranged for the sale to take place in May 1680 and, while awaiting this final disaster, lived in great penury, suffering from a recurrence of tertian fever, giving himself “entirely to his spiritual concerns, spending his whole time in acts of love and devotion to the Supreme Being, and thus,” as Boerhaave writes, “ended his course on seventeenth February 1680.”30 Rather in character, he “ended his course” without, so far as is known, leaving posterity any genuine portrait.

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Experiment and Observation Swammerdam made his will on January 25, 1680, leaving all his papers to Thévenot. A complicated sequence of events, involving deceitful translators, printers, lawsuits, the French King’s painter, Joubert, and Joseph de Verney, the eminent anatomist, ensured that they lay hidden until Boerhaave purchased them for the honor of his native Holland in 1728. He arranged, again in spite of the avarice of printers, for them to be published in 1737. In addition to publishing Swammerdam’s writings, Boerhaave also endeavored to determine the method he had used in his investigations. First and foremost, Boerhaave says, Swammerdam “affirmed nothing but what he saw and was able to demonstrate everything he affirmed. He in good earnest followed Bacon’s advice; for his opinions were the fruit of his experience, and he could effect the very things he maintained.”31 His cast of mind is shown by his praise of Harvey at the end of his History of Insects. “The illustrious Harvey,” he writes, focused on the natural world rather than on the books of others, and heaped scorn on those who thought it sufficient to be “wise with the wisdom of others, or learned with their learning.”32 Boerhaave also emphasizes the importance of Swammerdam’s “laboratory” apparatus. He used a specially designed bench for holding the lenses of his single microscope, starting with a low magnification and substituting lenses of higher and higher power. We can imagine him bending over this instrument in the heat of the midday sun, the sweat, as we noted above, pouring down his face. To prepare his specimens he used a tiny saw made from a watch spring, a pair of extremely fine and sharp scissors, feathers, exquisitely drawn-out glass tubes, minute tweezers, etc.33 He also developed effective techniques for preserving the organisms he wished to dissect and for injecting their vessels and other cavities with air or water to make them more visible. Some of these techniques he also employed in the investigation of muscles. Although the Book of Nature is subtitled History of Insects, it contains numerous chapters on snails and frogs. It is in these latter chapters that we read of Swammerdam’s pioneering experiments on muscle. In a chapter entitled “Experiments on the Particular Motion of the Muscles in the Frog; which may be also, in general, applied to all the motions of the muscles of Men and Brutes,”34 he describes the movements of both the heart and the gastrocnemius muscle (Fig. 7.2). In both cases he makes use of exquisitely constructed apparatus. When the sciatic nerve is “irritated,” the muscle contracts. The two pins are drawn toward each other (Fig. 7.2a). In the second case, contraction of the heart causes the air bubble to move down the glass tube (Fig. 7.2b). In the third (p. 114)

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Experiment and Observation case, contraction of the muscle does not cause any perceptible movement of the air bubble in the tube (Fig. 7.2c).

At the beginning of his account he admits to “many indissoluble difficulties” and remarks that we are far “from knowing the motion and effect produced by the subtle spirit that continually passes through the nerves into the muscles.” Is he being ironic, or faux naïf, for, as he points out later, his experiments show that there can be no subtle spirit coursing or otherwise in nerves! Unfortunately, although these experiments were demonstrated to many of the great and good of his time, they were not placed fully in the public domain until the Biblia naturae was published by Boerhaave in 1737. He notes “as a matter of great moment” that whenever nerves in a living body are irritated there is “immediately considerable motion in the muscles.” In particular he describes experiments on the nerves innervating the diaphragm of the dog and watching it heave and straighten. After discussing several other similar experiments, especially those using the frog gastrocnemiussciatic preparation (Figs. 7.2a and 7.2c), which he says he has demonstrated to the Grand Duke of Tuscany and his entourage, he writes, “Hence I propose it, as a matter worth considering, whether we should not reject the opinion, which supposes a spirituous matter to be necessary to excite muscular motion, and that it flows out of the brain.”35

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Experiment and Observation He remarks, further, that the experiments illustrated in Figure 7.2b and c make it difficult for those who believe that skeletal muscles contract by “inflation, fermentation or a kind of explosive motion.” He notes that, when the frog heart is in systole, the little drop of water in the tube descends. It follows that the heart is occupying less space. Vice versa, when the heart relaxes in diastole, the drop of water reascends to its original position. In the experiment shown in Figure 6.3c, however, contraction of

Figure 7.2: Swammerdam’s experiments: (a) A frog gastrocnemius muscle is enclosed in a glass tube and the sciatic nerve is squeezed with forceps. The muscle contracts and pulls the two pins together. (b) An excised frog heart is enclosed in a glass tube. As it beats the drop of water in the capillary tube moves up and down. (c) The gastrocnemius muscle is enclosed in a glass tube with the sciatic nerve protruding. When the nerve is stimulated and the muscle contracts the drop of water does not move. (From Swammerdam, 1737)

the gastrocnemius muscle results in little or

no movement of the water droplet. This experiment, Swammerdam confesses, is very difficult to carry through and very difficult to assess. Nevertheless, in consultation with Stensen, he is happy to conclude that a muscle does not increase in volume on contraction.36 But he remains somewhat doubtful. His experiments with the heart led him to think that far from retaining the same volume (as William Croone was later to assert), there is a diminution in volume when a skeletal muscle contracts. The question of whether skeletal muscle increased, decreased, or remained the same in volume remained a source of argument, as we shall see, throughout the course of the 17th century. He is on much firmer grounds when he criticizes the theory of animal spirit. He writes that those who argue that only a small quantity of animal spirit is required to account for his findings are refuted by considering “how often the motion of each muscle is restored by only stimulating, provoking or irritating the nerve…and this, when the nerve has been long cut off, and the requisite animal spirit dissipated, or grown weak, after many times discharging its duty; and when there is no further communication between (p.115) the nerve, brain and marrow.”37 He concludes that the case for animal spirit coursing down nerves cannot be sustained. Rather, he writes, “`the spirit’ as it is called, or that subtle matter…may with greatest propriety be compared to that most swift motion, which, when one extremity of a long beam or board is struck with a finger, runs with such velocity along the wood that it is perceived almost at the same instant at the other end.” There is no bulk flow through tubular nerves.

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Experiment and Observation But where does this mechanical impulse come from in the living animal? Swammerdam considers it comes from the spinal marrow, and he asks that we carefully note that he makes no distinction between voluntary and involuntary stimulation. He writes of the “continuous impulse of the arterial blood upon the marrow and the nerves.”38 But, beyond suggesting an experiment consisting in the injection of a “peculiar liquid” into the spinal marrow and then observing any muscular activity resulting, he leaves his investigation there. He feels that he has done enough to discredit the idea of animal spirit coursing along tubular nerves. How the brain and spinal marrow initiate the percussive motion he wishes to substitute for the flow of spiritual fluid he wisely leaves to future research. He ends his account of his groundbreaking experiments, experiments that, as we noted, he had demonstrated to the great and the good of his time, with his usual invocation to the Deity: “I am sensible, that all this time I have been, as it were, representing with a coal the sun’s meridian rays… [for] every true and valuable discovery is the gift of the Divine Grace, which God distributes as he pleases and makes manifest in his own time.”39

Microscopy If Swammerdam felt that, like Newton, he was only standing on the shore of a limitless ocean of natural science, if he felt, as he did, that to understand one had to look deeper into the nature of things than was Figure 7.3: Robert Hooke’s microscope. possible in his time, he was not From his Micrographia of 1665. alone. Although his remarkable discoveries depended, as we have just seen, on an obsessive, religiously motivated interest in the world of nature, they also depended on exquisitely designed equipment. Central to all his investigations was the magnification permitted by the lenses of simple microscopes.

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Experiment and Observation Microscopy was one of the great developments of the 17th century. Just as the telescope revolutionized astronomy and changed our understanding of our place in the cosmos, so microscopy changed our understanding of the living world. It revealed a universe of microscopic forms in a drop of pond water or in the sediment scraped from between the teeth of an old man—to use one of van Leeuwenhoek’s examples. Swammerdam was far from being the only worker in the Netherlands or, indeed, elsewhere to be fascinated by the world these early microscopes revealed. Four other names stand out in this regard: Robert Hooke (1635–1686), Nehemiah Grew (1641–1712), Marcello Malpighi (1628–1694), and Antoni van Leeuwenhoek (1632–1723). London’s newly formed Royal Society, established in 1660, played a central coordinating role. At its center stood Robert Hooke. His microscope is shown in Figure 7.3. Hooke was a remarkable man: anatomist, chemist, astronomer, architect, town planner, physicist, and microscopist.40 He was, unfortunately, overshadowed by yet a more remarkable man, Isaac Newton. Nevertheless, Hooke was sufficiently prominent for the Royal Society to make him Curator of Experiments. This meant that he was required to demonstrate a wide variety of experiments, both his own and those sent in by others, to the assembled savants. Among the experiments were those using the microscope (Fig. 7.3). Indeed, he was expected to make at least one microscopical demonstration at each meeting of the Society. The 17th century was fascinated by the world beneath the visible. What did a flea really look like? A pollen grain? Cork (Fig. 7.4)? These early microscopists were, as Brian Ford points out, in a sense, “macroscopists,” fascinated by the detail of what lay just below naked-eye visibility.41 The drawings of the images that Hooke demonstrated with his simple microscope were ultimately collected in his Micrographia of 1665. The most important concept to come from his work was that of the “cell,” so named because he saw a resemblance between the honeycomb arrangement of cork tissue and the cells monks inhabited in monasteries. A perusal of the Micrographia shows, however, that although he examined with a wide-ranging curiosity everything from the “teeth of a snail” to the “white feathered wing of a (p.116)

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Experiment and Observation moth,”42 he included no images of the nervous or muscular systems. However, this does not mean that he had not examined these tissues. We shall see in the next chapter that he took part in the debates centering on William Croone’s theory of muscular contraction. His microscope seemed to reveal that the fine structure of skeletal muscle resembled a “necklace of hollow glass beads.” Like so much early microscopy, faulty specimen preparation led to illusory images. Inspired by these faulty images Hooke devised an experiment where a chain of small bladders fastened together showed how the fine structure he thought he had detected might lead to contraction.43 We shall return to this when we come to discuss William Croone’s theory in Chapter 8.

The interests of the second of Figure 7.4: Cork cells from the these great 17th-century Micrographia. microscopists, Nehemiah Grew, were largely botanical. His major work, the Anatomie des plantes, was published in 1675 and contains the first known description of the microscopic form of pollen. Although he attended Leiden University, the center of medicine and anatomy, and, although his MD thesis was entitled Disputatio medico-physica…de liquore nervosa, he is not known to have applied his microscope to investigate the fine structure of the neuromuscular system. Like Jan Swammerdam and many of the other early microscopists it seemed to him that the revelation of a world lying beneath the range of the unaided human eye provided yet further evidence for the exquisite handiwork of the Almighty. Thus, in 1701, he published Cosmologia sacra, in which he attempted to show how the new discoveries supported the teachings of the Bible.44 Let us, however, turn to the third great microscopist listed above, Marcello Malpighi. Malpighi was most certainly concerned with the neuromuscular system and is, indeed, regarded as one of the founders, if not the founder, of neurohistology.45

Marcello Malpighi (1628–1694)

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Experiment and Observation Marcello Malpighi (Fig. 7.5) was born at Crevalcuore near Bologna in 1628. It is said that he became fascinated with the microscope and microscopy while still a boy. His early interests also included philosophy and medicine. In 1649 he began his professional studies at the University of Bologna and in 1653 graduated in both philosophy and medicine. In 1656, at the early age of 28, his talents were recognized by the offer of a chair in theoretical medicine at Pisa. Here he met another newly appointed professor: the mathematician Giovanni Borelli (1608– 1679). They became fast friends and both became members of the short-lived Accademia del (p.117) Cimento, the Italian scientific society founded in 1657 and disbanded in 1667. We shall see, in the next chapter, that Borelli, influenced by his friend, became intrigued by the problems presented by animal movement and the action of muscles. He is nowadays regarded as the father of biomechanics. He plays, as we shall see, a significant role in the physiological odyssey outlined in this book.

Malpighi did not stay long at Pisa. He returned to Bologna in 1659 and then, in 1662, on the recommendation of Borelli, accepted a chair at the University of Messina in Sicily. After 4 years in Messina he returned to Bologna. The years in Bologna formed the climax of his scientific career, but they were not without opposition: his views offended the traditionalists. In 1684 his villa was burned down and his microscopes and papers were

Figure 7.5: Marcello Malpighi from an oil painting by A.M. (From Wikipedia Commons, ‹factspage.blogspot.com/ 2011/10/marcello-malpighi.html›)

destroyed. He was evidently under considerable strain. He continued his teaching, research, and medical practice but his health began to deteriorate. However, the Roman Church in this instance came to the rescue of science. In some small reparation for the treatment of Galileo, Pope Innocent XII invited Malpighi to Rome, not this time to be shown the instruments of torture but to become his personal physician. While there he was also made a Count and elected to the College of Medical Doctors. He died in 1694. Page 17 of 39

Experiment and Observation Although Malpighi published a treatise on plants, Anatomia plantarum (1679), and is believed to have corresponded with Nehemiah Grew, his main fame and interest to us in this book is his work on animal tissues. He is regarded, with justification, as the founding father of animal histology, and a number of histological structures still bear his name: Malpighian corpuscles in the kidney, the Malpighian layer in the skin, Malpighian tubules in the excretory system of insects etc. His most important contribution was the discovery of the capillaries linking arterioles to venules, thus confirming and completing Harvey’s cardiovascular theory. He also played a significant part in the early development of embryology, making use of the microscope to follow the development of the chick. In addition to all this, he did not neglect to study the brain. Malpighi’s pioneering histology was made with a compound microscope on fresh “unfixed” tissues. It is not surprising, therefore, that, like the other early microscopists, he observed numerous artifacts and illusions. In addition, chromatic and spherical aberrations in early compound microscopes ensured that microscopists were confused by all sorts of multicolored haloes. Another persistent illusion, largely due to tissues being “unfixed,” was that they were composed of lines and agglomerations of globules. As late as 1824 Dutrochet was writing that “everywhere, in effect, one finds in animals only globular corpuscles, now arranged in linear and longitudinal series, now in confused agglomeration.”46 Thus, when he came to study the microscopic structure of that most intricate of organs, the brain, Malpighi was bound to be confused. He was not, however, put off by the difficulties presented by brain histology. He writes that he repeatedly dissected the brain for both macroscopic and microscopic examination.47 He also made much use of the comparative approach. When he could not make sense of the structures in the human or mammalian brain he turned his attention to fish. He writes, for instance, that, although he could not understand the structure of the corpus callosum in “higher animals,” he could see that it is made of small fibers in fish. He uses the same comparative approach to make sense of other brain tracts and structures.48 His preparative techniques for microscopy included removing the meninges and flooding the exposed surface with ink to increase the contrast. He also writes that in order to see the structure more clearly, the brain should be boiled. It is thus perhaps not too surprising that what he saw is now understood to be mostly artifact. Nevertheless, in the four chapters titled De cerebri cortice of his 1666 treatise De viscerum structura exercitatio anatomica,49 there is considerable material on the microscopic structure and function of the cerebral cortex and other parts of the brain.

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Experiment and Observation He writes that he has discovered that the cerebral cortex consists of a mass of very minute glands, closely fitted together so that they form the surface of the brain. Similar glands, he writes, can be observed (after moderate boiling!) in other parts of the brain—in the cerebellum, pons, etc. From the inner surface of the cortical glands, he goes on, there spring nerve fibers, which resemble vessels. The white medullary substance of the brain consists of bundles of these fibers.50 He suggests that these fibers “serve as vehicles for the succus nerveus.” He draws an analogy with plants. We remember that his final major publication was on the anatomy of plants. He suggests that the cortical mass is analogous to the soil from which the fibers draw nourishment. He supports this idea by observing that when “the brachial nerve is sectioned, there emanates a certain copious juice resembling egg albumen, which coagulates on heating.”51 Is this the first observation of what we now call axoplasm? Unfortunately, Malpighi gives no illustration of his globular cortical histology in his 1666 treatise. However, a very well-known figure appeared a few years later in Bidloo’s 1685 anatomy text (Fig 7.6).52 It is claimed that Malpighi authorized this figure, and it is certainly a good representation of the description given in the Viscerum structura. Did Malpighi see, for the first time, cortical cells and axons and mistake them for minute glands and nerve tubes? Clarke and Bearn,53 who repeated Malpighi’s work using 17th-century techniques and microscopes, think not. They conclude that what he saw and had illustrated in Bidloo’s text was an artifact of the poor preparative techniques, including the ink technique, and the achromatic microscopes of the time. Nevertheless, Malpighi’s glandular model of the cortex proved very popular and his figure, often considerably corrupted, was transmitted well into the 18th century. It seemed to confirm that the brain was a complex gland secreting “animal spirit” into nerve tubes directed to the rest of the anatomy. (p.118)

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Experiment and Observation Malpighi’s researches into brain Figure 7.6: Malpighi’s “cortical glands”; structure, both at the microscopic from Bidloo, 1685. and macroscopic level, led him to be quite scornful of “the most famous Cartesius.” His neurophysiology, he writes, “bristles with difficulties.” It can in no way be reconciled with the neuroanatomical and/or neurohistological reality.54 He, moreover, will have nothing to do with the ancient ventricular theory. Traditionalists, he writes, have worshipped the ventricles and rete mirabile, but contemporary research has “dismissed them from (their) lofty service to become a pair of snuffers, or, so to speak sewage drains of excretions.”55 Rather, he says, the operation of the brain remains a mystery, that he cannot believe it can be responsible for the subtleties of the senses and suchlike phenomena, and that all that can be said is that “a certain juice is secreted by the cerebral and cerebellar glands” allows the brain to react to outside events.

Antoni van Leeuwenhoek (1632–1723) It is, however, to Antoni van Leeuwenhoek (Fig. 7.7) that we owe the first image of the nervous system that we can accept today as representing reality rather than artifact. Van Leeuwenhoek is another of the great geniuses of the Dutch 17th century. What was it about the Netherlands in those days that nurtured so many of the inventors of the modern world? Descartes found peace and tranquility, first in Amsterdam and the Hague, and later in small towns in north Holland, especially Egmond am Zee. Swammerdam, after travels in France, came home to Amsterdam to investigate the minutest (or so he thought) of God’s creatures. And now, lastly, Antoni van Leeuwenhoek, a Delft draper’s son, was to become the most adept microscopist of the age. It obviously has something to do with an escape from

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Experiment and Observation the dead hand of ecclesiastical authority, although we can see, especially in Swammerdam’s case, the power that religious ideas still held. It has also, in both van Leeuwenhoek’s and Swammerdam’s case, something to do with that Baconian turning away from a Scholastic focus on the authority of men and their books towards nature herself that we noted at the beginning of this chapter. It is fascinating to observe, in this regard, that van Leeuwenhoek and that other great exponent of seeing things clearly, Johannes Vermeer, were exact contemporaries. It is unlikely that in the small city of Delft they would not have known each other and become friends. Indeed, it has been suggested that two of Vermeer’s best-known paintings— The Geographer and The Astronomer—show the 32-year-old

Figure 7.7: Antoni van Leeuwenhoek by Jan Vekolje, c. 1670. (From Wikimedia Commons, ‹en.wikipedia.org/wiki/ File:Jan_Verkolje__Antonie_van_Leeuwenhoek.jpg›)

van Leeuwenhoek.56 The likelihood that Vermeer and van Leeuwenhoek were friends is increased by the fact that van Leeuwenhoek was an executor of the great painter’s will when he died in 1675.57

Who, then, was Antoni van Leeuwenhoek? He was born in the autumn of 1632 in Delft, a small port close to The Hague. The wonderful paintings of Vermeer give us a living impression of what it was like in van Leeuwenhoek’s time. (p.119) Antoni was brought up in a tradesman’s family of very modest means. He received no higher education and knew no languages except his native Dutch. At the age of 16 he was apprenticed to a Scottish textile merchant working in Amsterdam. It was here that he first encountered magnifying glasses. They were used to count threads in the textiles to determine and control quality. In 1652 he returned to Delft and set himself up in business as a draper, but he was a young man of insatiable curiosity and blessed with acute eyesight. Microscopy fascinated him.

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Experiment and Observation In 1668, during his first and only visit to London, he was shown a copy of Robert Hooke’s Micrographia. He was hooked. He set about making microscopes of his own. This work lasted the rest of his unusually long life and he kept his techniques secret. He is nowadays believed to have constructed his (at the time) incomparable lenses, not by grinding but by heating small rods of soda-lime glass. He is known to have made over 400 of these simple microscopes, of which about 10 have survived into our times. Although compound microscopes had been invented many years before at the end of the preceding century,58 they were subject to all the optical imperfections mentioned above. Van Leeuwenhoek, however, perfected the fashioning of minute “bubble” lenses, scarcely larger than the head of a dressmaker’s pin, and inserted them into a small metal plate (Fig. 7.8). He achieved magnifications of up to 200×. The young van Leeuwenhoek soon began sending his observations, often in critical response to the figures in Hooke’s Micrographia, to “men of eminence” and, in particular, to London’s Royal Society, where they were translated into English and published in the Transactions. Among these communications was the first drawing of a transverse

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Experiment and Observation section of a nerve seen through a simple microscope (Fig. 7.9). Van Leeuwenhoek had taken fresh bovine optic nerve and cut thin slices (≤0.2 mm thick) and placed them under the lens of his microscope. He made drawings and sent them to London, where they were engraved and printed in the 1675 Philosophical Transactions of the Royal Society.59

The publication of Figure 7.9 in the Transactions marks, as Ford observes, “a critical moment in the history of neuroscience.”60 It is interesting to note, moreover, that van Leeuwenhoek was encouraged to examine the nerves precisely because of the ongoing controversy on their nature: were they hollow tubes capable of transporting animal spirits, or were they solid? Thus, in his letter to the Royal Society accompanying his specimens, he writes, “Dr of anatomy Schravensande…mentioned that since ancient times there has been some dissension among the learned about the optic nerve and that some anatomists affirmed [it] to be hollow; and that they themselves had seen it to be hollow, through which they would have animal spirits…pass into the brain. I therefore concluded that such a cavity might be seen by me…I solicitously viewed three optic nerves of cows, but could find no hollowness in them.”61 In the published communication, he starts by observing that, having told “Dr Schravensande that I could perceive no cavity in the Optic nerve, he told me, that Galen had on a clear sun-shiny day seen a hollowness therein, encouraging me to view that nerve again with more attention.”62

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Experiment and Observation Van Leeuwenhoek admits, in his Figure 7.8: Simple microscopes of this 1675 publication, that the optic type were developed by van nerve does contain a cavity, but Leeuwenhoek in the 17th century. The not a single hole, rather “very specimen was attached to the tip of the many which made it resemble a metal holder and adjusted by the screws. Leathern Sive [sic], wherein are It was viewed from the other side of the big and small holes not round, metal plate through a tiny “bubble lens” nor regularly positioned, but inserted into the plate. The whole rather like holes in a piece of assembly was little larger than a postage moistened parchment, which on stamp. stretching are irregularly spaced and of various shapes” (Fig. 7.9). However, he continues with his earlier opinion that the interior of the nerve consists of “soft fluid globules and that these globules by drying of the Nerve are most of them exhaled.” After considering whether each of the cavities in the nerve might have been a hollow filament, he concludes that it is more likely that they are the remains of these fluid-filled globules. Transmission of images (p.120) to the brain, he concludes, might be compared to a finger disturbing the surface of water in a “tall Beer-glass.” The glass represents one of the filaments of which the nerve is composed and the water in the glass the globules of which the filament is composed. A touch on the surface of the water is transmitted by pressure to the bottom of the glass or, in the analogy, along the nerve filament to the brain.

Figure 7.9: Van Leeuwenhoek, 1675: transverse section of bovine optic nerve.

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Experiment and Observation Van Leeuwenhoek’s fame grew rapidly. He sent many hundreds of letters describing his observations to the Royal Society. He was visited by many of the eminent figures of the age: Huygens, Boerhaave, Descartes, Leibniz, Christopher Wren, Queen Anne, Spinoza, Frederick the Great. Tsar Peter the Great invited him to sail off Delft in his boat, and van Leeuwenhoek showed him the blood circulating in the capillaries of an eel.63 His insistence on making his own observations caused Leibniz (1646–1716) to remark (famously), “I prefer a Leeuwenhoek who tells me what he sees to a Cartesian who tells me what he thinks.” Did van Leeuwenhoek continue his researches into the neuromuscular system after this initial breakthrough? The answer is yes. In 1682 he sent Robert Hooke an image of bovine muscle, which clearly shows the myofibrils within a fiber and the cross-striations (Fig. 7.10), and in one of his very last letters, written at the age of 85 in 1717, he writes that he had “three cows and one sheep brought to my house, that I might extract from thence the nerves.”64 He describes how he sectioned them with a sharp razor, taking great care to cut at right angles to their length, and saw that the nerve fibers were hollow! But, he says, this hollowness, this wonderful sight, disappears; it “evaporates in less than a minute and cannot be restored.” Clearly his specimens were drying out. He describes this evanescent hollowness “as if we were to pierce many holes in a paper with a small needle, and held them up against the sun.” He shows what he sees in a remarkable figure (Fig. 7.11). It shows a bovine or ovine nerve cut in transverse section. The epineurium surrounding the entire fiber and the perineuria surrounding each of the contained axons are clearly shown. The axons are shown as hollow tubes. Within each tube, he writes, he saw “an oblong line” (presumably the condensed axoplasm) and this he succeeded in making “the limner” see. He is evidently astonished and knows that what he reports goes against the prevailing orthodoxy. “I am sensible,” he writes, “that what I relate here will not be credited by some persons.…I am indeed, by the vulgar, treated as a conjuror, and that I publish descriptions of objects which do not exist in nature, but we will leave these men to talk in their own way.”65 We noted above Leibniz’ comment on van Leeuwenhoek’s Baconian view of his work: show, not say. By all accounts he was a very kind and sociable man, unwilling to carry out the “heroic” vivisections of a Vesalius or a Malpighi. He was not one for building theories (or, for that matter, demolishing theories) on the basis of his observations. Whether he believed that animal spirit flowed along the tubes which he saw in his 1717 microscopy, he did not (in print at least) say. That he left to the theoreticians, some of whom we shall discuss in the next chapter. Before turning to that chapter, however, there is one last anatomist we should consider: Niels Stensen.

Niels Stensen (Nicolaus Steno) (1638–1686)

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Experiment and Observation Niels Stensen (or Nicolaus Steno; Fig. 7.12) is an ambiguous figure. In the first part of his life he displayed a wide-ranging curiosity. He, also, was determined to follow in the footsteps of Francis Bacon and report only that which he could verify with his own senses. “One sins against the majesty of God,” he writes in his student notebook, “by being unwilling to look into nature’s own works and contenting oneself with reading others…. From now on I shall spend my time, not on musings, but solely in investigation, experience and recording of natural objects.”66 But, like so many 17th-century savants, his mind was in thrall to the religious culture of the time. He could not break free from the power of the theological thought-world, so that in the second part of his life, he turned from the spirit of free enquiry to the consolations of religion. Ultimately he joined the Roman Church and ended a Bishop. Stensen was born in Copenhagen on New Year’s Day 1638 (old calendar) or January 11, 1638 (new calendar). He was thus another of that coterie of brilliant men (and (p.121) women) who lived or at least originated in the northwestern corner of the European land mass. He was the son of a goldsmith (from a family of preachers) who died when Niels was 6 years old. His mother quickly married another goldsmith (who just as quickly died) and then a third, so we can imagine that the young Stensen’s life was not easy. There were financial problems, and in 1654 plague struck Copenhagen and he lost many of his young friends. Niels had, however, a brilliant mind and a wide-ranging curiosity. In spite of his unpropitious beginning, his stepfather saw that he was given an excellent education. In 1655 he entered the University of Copenhagen to study medicine. The notes he took at this time, known as the Chaos Notebook, were discovered in 1946 and show that the young Stensen received a wide-ranging education at the university and that he read or skimmed over 75 books, including those of Descartes, Galileo, Kepler, Borelli, and Bacon.67

Times were not easy in Copenhagen. In 1657 King Frederick III of Denmark was foolhardy enough to declare war on Sweden. The Swedes retaliated by invading Denmark, and in the exceptionally cold winter of 1657–8 they crossed the frozen sea from Jutland to the island of Zealand, on which Copenhagen is built. Peace was negotiated, but in 1659 war broke out again and Copenhagen was once more besieged. The emergency lasted until 1661 and the university (p.122)

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Experiment and Observation closed while its students were organized into defensive brigades. When, ultimately, peace returned, the young Niels decided the time had come to see a bit more of the world. He went first to Rostock and then to Amsterdam, where he continued his medical studies. In Amsterdam, Niels came into contact with several able anatomists and brilliant students, including Jan Swammerdam. From Amsterdam he traveled to Leiden, where he completed his medical degree and also came to know Baruch Spinoza (1632–1677), who lived not far away in Rijnsberg. He ended his student years by studying anatomy in Paris in 1663–5, and while there he became part of Thévenot’s circle.

Figure 7.10: Van Leeuwenhoek, 1682: muscle “strings” of a cow: “About nine times smaller than my beard, containing about 5 000 small muscle fibres/inch2.” But even within these strings van Leeuwenhoek was able to show (Fig. 1) a hundred or so “inward filaments” [our myofibrils] (NOPQ). Fig. 2 shows the muscle flattened and “teased” after moistening with a “little spittle.” Fig. 3 shows what are probably two of Leeuwenhoek’s ‘inward filaments’ teased out of the muscle. Fig. 4 shows the similar structure that van Leeuwenhoek observed in muscle derived from a codfish. (Letter from Delft to Robert Hooke, March 1682 in Philosophical Collections of the Royal Society, p.161.)

Figure 7.11: Van Leeuwenhoek, 1717: cross-section of bovine or ovine nerve. From Leeuwenhoek, 1717 (in Leeuwenhoek, 1807, plate XIX).

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Experiment and Observation Melchisédec Thévenot (whom we met when discussing Swammerdam above) had become librarian to Louis XIV and was seriously rich. He was thus able to provide financial support for young scholars. The weekly meetings in his house were later to form the nucleus of the French Academy of Sciences. It was in these meetings that Stensen met Jan Swammerdam again and may well have discussed the latter’s experiments (and their implications) on the frog nervemuscle preparation.68 Thévenot was able to do something else for Stensen. He introduced him to his cousin Marie Perriquet, who had been part of the group surrounding Blaise Pascal. Stensen later acknowledged that intense conversations with her had helped him towards his later conversion to Catholicism. But, from our point of view in this book, the most important outcome of his stay in Paris was a lecture he gave in 1665 to Thévenot’s group on the anatomy of the brain. We shall discuss this further below. The title page is shown in Figure 7.13.

But Stensen’s wanderlust was still not satisfied. From Paris he went south, first to Montpellier (where he met William Croone and other English savants who were avoiding the plague in London) and then to Pisa. He stayed in Pisa for a year, from 1665 to 1666, thus overlapping with Giovanni Borelli, who, at that time, held the Chair of Mathematics (see Chapter 8). From Pisa he traveled to Florence, where he came to the notice of Ferdinand II, the Grand Duke of Tuscany, who made him his court physician and anatomist at the Santa Maria Nuova hospital. Here, in

Figure 7.12: Niels Stensen, attributed to the court painter Justus Sustermans. (Wikimedia Commons, ‹en.wikipedia.org/ wiki/ File:Portrait_of_Nicholas_Stenonus.jpg›)

1667, one of the major events in his life occurred: he converted from the Lutherism of his northern upbringing to Catholicism.69 Almost at the same time as this momentous event occurred, he received a letter from the King of Denmark (p.123)

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Experiment and Observation inviting him to take up a post in anatomy at the University of Copenhagen. But, on learning of his conversion to Catholicism, the offer was suspended and Stensen remained in Tuscany. Later, however, in 1668, he set out for Denmark, hoping that the suspension would be lifted. He visited Malpighi in Bologna on the way, and came to rest not in Copenhagen but in Amsterdam, where he waited to hear whether his invitation had been confirmed. Ultimately, learning that no letter of appointment was likely and missing perhaps the sunshine and religion of Tuscany, he returned to Florence. In 1672, however, the King’s religious scruples were overcome and he was invited back to Copenhagen as Royal Anatomist. Niels, however, was becoming increasingly absorbed in his religious life and less and less interested in anatomy. In 1674 he returned once again to Florence where, in April 1675, he was consecrated a priest. In 1677 Pope Innocent XI appointed him Figure 7.13: Title page of Stensen’s apostolic vicar of northern lecture on the anatomy of the brain. missions and Bishop of Titiopolis. By all accounts he was a dedicated priest and bishop, devoted to the scattered remnants of Catholicism in northwestern Europe. In 1685 he died in acute pain from gallstones.70

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Experiment and Observation It has been argued that Stensen’s early years in his father’s and stepfathers’ workshops influenced his later work. He learnt, it is suggested, the importance of detail and of overall design. It could well be that this early emphasis on shape —morphology—helped orientate his interest and great success as an anatomist. This success came early: while still a student at Amsterdam he made his first significant anatomical discovery. While dissecting a sheep’s head he discovered the duct that connects the parotid salivary gland to the mouth—now called in his honor the ductus stenonianus. This discovery shows us two things: first, that Stensen was a careful and observant dissector, not afraid to dispute the authority of his seniors (his tutor Blasius at first told him that he had made the duct himself by forcing his probe into the tissue), and second, that he was from the first interested in brain anatomy. His intention, when making his discovery, was to dissect the sheep’s brain, and he followed this up by dissecting a dog’s head, partly in order, it must be admitted, to confirm the position of the duct. In 1662 Descartes’ L’Homme was published in Leiden, and Stensen, who was at that time an admirer of the great French philosopher, was one of its earliest readers. He was disappointed: “I truly doubt whether a brain like that described [he refers to Descartes’ figures] is ever to be detected.”71 But, before making further contributions on the brain itself, Stensen published important work on cardiac and skeletal muscle (Fig. 7.14). He showed, against much conventional opinion, that the heart was a muscle like other muscles, not the source of “a dark fire” responsible for the body’s heat. Examining carefully the structure of both cardiac and skeletal muscle, he showed that contraction is due to the “flesh” and not the “tendon.” Stensen’s work on muscles was published as Nova musculorum & cordis fabrica (New Structure of the Muscles and Heart) in 1667 and Elementorum myologiae specimen (Specimen of Elements of Myology) also in 1667.72 Stensen continued his work on muscles when he arrived in Tuscany and was able to confirm Jan Swammerdam’s finding that muscles did not increase in volume during contraction. He maintained, on the basis of his dissections, that the flesh (contractile elements) of a muscle was formed of fibers of a dual nature: the center was contractile, the two ends were tendinous.(Fig. 7.15). It was here that Stensen broke with tradition. He proposed that the fibers lined up in the muscle to form parallelepipeds between parallel tendon plates (Fig. 7.16A). When contraction occurs, the contractile or, in his term, “fleshy” walls of the parallelepipeds move in such a way that the parallelepipeds tend towards rectangular prisms (Fig. 7.16B,C), thus causing the tendon plates to slide over each other in parallel planes. The muscle will shorten and appear to (p.124)

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Experiment and Observation increase in volume. But this is only an appearance. The parallelepipeds, he argues, retain much the same volume. Thus Stensen satisfies Swammerdam’s (and, later, Charleton’s) demonstration that muscles do not increase in volume on contraction. The significance of Stensen’s idea was not recognized until the 20th century. It was only then, with the sliding filament theory of muscle contraction, that something similar to Stensen’s theoretical insight received (albeit at the nano-level) some evidential basis.

Kardel, Stensen’s major biographer, believes that in all his work on cardiac and skeletal muscle Stensen was, from the first, concerned to find anatomical evidence to confirm or disconfirm the animal spirit

Figure 7.14: Title page of Stensen’s Elements of Myology.

theory of locomotion.73 He was, in addition, ambitious to show, as he writes in the Elements of Myology, that astronomers need have no monopoly on applying mathematics to movement: the movements of muscles, he insists, like those of the heavenly bodies, are equally open to mathematical analysis.74 But it is his famous lecture on the brain in Paris, mentioned above, that is of most interest to us in this book. The lecture, which included a few large diagrams, is taken

Figure 7.15: Diagram of skeletal muscle from Stensen’s Elements of Myology.

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Experiment and Observation (p.125)

Figure 7.16: (A) Stensen’s concept of muscle structure as sketched in a letter to Thomas Bartholin in 1663. (B) Stensen’s geometrical analysis of the movement of muscle microstructure (see text). (C) The contractile fibers (BC, FG, etc.) are lined up in this 3D diagram between sets of tendons (AB, GH, etc.). (D) Stensen’s concept of pinnate muscle microanatomy. (B, C, D from Elements of Myology delete

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Experiment and Observation by some as the true starting point of the modern era in brain research. It was given, in 1665, in French, at one of the weekly meetings at Thévenot’s house and was first published (in French) in 1669.75 In many ways it sets out a program of research that has been followed ever since. Stensen starts by remarking that the brain is the most cleverly constructed of all organs and that he wishes it was as well understood “as many philosophers and anatomists imagine it to be.” In fact, he asserts,

Figure 7.17: Sagittal and coronal sections of the human brain from Stensen’s 1669 Discours.

we know next to nothing about it. All that can be said is that it consists of two substances, a White and a Grayish.…[but anatomists] are ignorant of what those substances are…and as for the Ventricles or Cavities of the Brain…they are no less unknown than its Substance…some Anatomists lodging in them the Spirits, others making them receptacles for the Excrements of the Brain; and both perplex in assigning the source and issue of the Excrements, and of the Spirits, and of the manner of the production of the latter.76 Stensen goes on to criticize the psychophysiology of both Thomas Willis and René Descartes. Despite congratulating Willis on publishing the best figures of the brain, he finds “very obnoxious” his view that the common sensorium is located in the corpus striatum, the imagination in the corpus callosum, and the memory in the “greyish matter that encompasses the white.” He is yet more dismissive of Descartes. He writes that “that Philosopher hath rather devised, in his Treatise of Man, such an engine that performs all the actions Men are capable of than described Man as he really is.” We might interject, in parenthesis here, that this is perhaps all that Descartes intended. Stensen is also scathing about Descartes’ pineal. He argues that Descartes’ anatomy is entirely imaginary and that in reality it could not do what Descartes demands that it should! He goes on to insist, “There only two ways we can learn to understand a machine. The first is by the master who built it showing us how it is made. The second is to strip it down to its smallest parts and then to investigate each on its own and then in relation to each other.”77

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Experiment and Observation Stensen concludes his masterful lecture by arguing, following Bacon, for a collective effort, not blind belief in ancient authority; that reproducible dissections be made; that careful drawings be made of them (Fig. 7.17) and an unambiguous terminology developed. “Last of all,” in the words of the Royal Society reviewer, when all this he hath discoursed of is done, that is but the least of what is to be done…there must be Dissections and Examinations made of as many Heads as there are different species of Animals, and different States and Conditions of each kind; since that in the fetus’s of Animals it will be seen, How the Brain is formed; and what could not be seen in sound and entire Brains, may be seen in such, as have been changed by sickness.78 It is clear that the Royal Society reviewer, whoever he was, is in full and enthusiastic agreement. Few would dissent today.

(p.126) Concluding Remarks In this chapter we have seen how the Baconian impulse to turn from the books of men to that of nature motivated some of the great biomedical researchers of the 17th century. We have also seen how religious motivation both energized and obstructed this research. We have seen how the early microscopists, Swammerdam in particular, believed themselves privileged beyond their predecessors in seeing further than they into the works of the Almighty. Even the untheoretical van Leeuwenhoek recognized that his microscopic observations pointed towards a higher truth. On the title page of his Collected Works is a quotation from the Dutch poet, Jacob Cats: “When thou beholdest the curious works of nature, do thou not be content with merely gazing at their beauties, (and canst thou possibly dwell on them without looking higher?) but raise thy thoughts to the contemplation of Him by whom everything that is fair and beautiful was created.”79 In England many of the Puritan sects emerging in the early 17th century believed themselves to be living at the end of time. The end of the world was imminent and would be succeeded by the Second Coming, when Christ would reign for 1,000 years before the final Judgment Day. It was good, therefore, to know as much as possible about the Creator, as revealed in His creation, before these apocalyptic days arrived. On the continent of Europe, theological passions raged just as strongly. The work of both Swammerdam and Stensen was brought to an untimely end, though in different ways, by these emotions.

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Experiment and Observation It was from this mixture of motives that some of the great biomedical discoveries of the age emerged. We have seen, in particular, how the passion to understand the secret structures of nature, lying beyond the sight of the unaided eye, led to discoveries in the microanatomy of the nervous system, which put in question the old, time-honored, animal spirit doctrine. In the next chapter we shall look at some of the theoretical responses to these anatomical and experimental findings. Notes:

(1) Indeed there is good evidence to show that he was hoping to set up a new syllabus to replace the old trivium and quadrivium, which he and others of his time had endured. See Gaukroger, 1995. (2) Bacon, 1597:“Of Studies.” (3) Bacon, 1605, IV (5). (4) Ibid., XX (2). (5) Bacon’s proposals for a new society of scholars constitute the Novum organum published in 1620 as the second part of The Great Instauration. (6) Sprat, 1667, p. 113. (7) Fabricius, 1603. Although Fabricius had discovered the valves, he had not recognized their physiological significance. This was left for his pupil. (8) Aubrey, 1999, p. 132. (9) Aubrey, 1999, p. 129. (10) Aubrey, 1999, p. 130. (11) In exercise 55 of On the Generation of Animals, he writes “the whole seems to be referrable to one principal, viz.: the perfection of nature, who in her works does nothing in vain” (Harvey, 1651). (12) Boyle, 1688, p. 157. (13) Kepler, at the end of the preceding century, had fought long and hard to fit the movements of the planets into circles and was upset to find that the best fit for their motion was that of an ellipse. (14) Harvey, 1628. p. 150. (15) Ibid., p. 92. (16) Quoted in Bono, 1990, p. 342. Page 35 of 39

Experiment and Observation (17) Whitteridge, 1959. (18) Ibid., pp. 115–116. Harvey also toys with the Fabrician analogy (also Galilean) of wet ropes raising weights. He asks whether something similar on the microscale might be responsible for muscle contraction. (19) Ibid., pp. 101–103. (20) Ibid., p. 111. (21) Ibid., p. 109. (22) Ibid., p. 151. (23) Boerhaave in Swammerdam, 1737, p. 1. (24) Swammerdam, 1737. (25) Ibid., part 1, p. 159. (26) Boerhaave, ibid., p. vii. Antoinette Bourignon’s best-known work is the 1667 Light of the World. An English translation (anonymous) was published in 1696 and reprinted in 1863 (London: Sampson Low, Son and Co). Antoinette Bourignon was born to a rich Catholic family in 1616. Unwilling to marry, she left home to live a wandering life. She taught a quietist mysticism, insisting that the things of this world were a mere distraction from man’s proper vocation: to love and contemplate the Deity. In her XIXth letter she insists that an interest in earthly things distracts us from the truth: “For whosoever deeply reflects upon his own Being, his Origine, and the End for which he was Created, will find it impossible to seek after things sensual and Earthly, knowing them to be so vile, so miserable, and of so short continuance: thus might he disengage himself of all, that he may love God alone, who is the only amiable object” (Bourignon, 1703, part 2, p. 109). (27) Lindeboom, 1974, p. 191. Bourignon goes on to chastise Swammerdam, saying that “from the narrative you give me of your life, I see that all has been only pastimes of Satan.... for what profit would it be for a man to know all the interior parts of the body…in view that that only regards the flesh and muscle…?” (p. 192). Bourignon’s letter also advises Swammerdam not to marry a girl to whom he was attracted. Lindeboon shows that this was Margarita Volckers, who, after Swammerdam’s death, married a Leiden doctor. In spite of Antoinette’s advice to put away worldly things and study to become a Christian, there is some evidence that Swammerdam did not entirely give up his scientific interests. (28) Boerhaave in Swammerdam, 1737, ibid., IX.

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Experiment and Observation (29) Ibid., xii. (30) Ibid., xiii. (31) Ibid., xvi. (32) Swammerdam, 1737, part 1, p. 137. (33) See Cobb, 1990. (34) Swammerdam, 1737, part 2, p. 122–132. (35) Ibid., p. 124. (36) Ibid., p. 128. (37) Ibid., p. 124. (38) Ibid., p. 125. (39) Ibid., p. 132. (40) See Inwood, 2002; Jardine, 2003. (41) Ford, 2007, p. 29. (42) Hooke, 1667. (43) Hooke, 1678, p. 401. (44) Grew, 1701. (45) See Meyer, 1967. (46) Dutrochet, 1824. Quoted in Hall, 1969, vol. 2, p. 185. (47) Malpighi, 1665. (48) Ibid., pp. 7–9. It is not clear to which tracts in the fish brain Malpighi is referring. The corpus callosum, as it is now defined, does not exist in fish. (49) Malpighi, 1666. See also Belloni, 1968. (50) Ibid., p. 53. (51) Ibid., p. 12, trans. Meyer, 1967. (52) Bidloo, 1685. (53) Clarke and Bearn, 1968.

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Experiment and Observation (54) Malpighi, 1669, p. 12. (55) Ibid. (56) See Westermann, 2003. (57) Robert Huerta (2003) gives a fascinating account of the interaction between art and science in the Dutch 17th century in his book Giant of Delft. It is also suggestive to note the interrelationship between the construction of microscopes and the construction of camerae obscurae, both of which involved “pinhole” lenses. Some see the invention of the latter as responsible for the great verisimilitude of the paintings of Vermeer and others in the Dutch 17th century (see Hockney, 2001). (58) The earliest known compound microscopes appeared in the 1590s. The socalled Janssen microscope (named for its inventor) was a simple tube giving magnifications of up to about 20×. It is regarded as the forerunner of both the telescope and the compound microscope. The first known drawing of a compound microscope comes from the diary of the Dutchman Isaac Beekman, dated 1625. (59) Van Leeuwenhoek, 1675, p. 378. See Chapter 2, Note 9. (60) Ford, ibid., p. 31. (61) Quoted Ford, ibid. (62) Van Leeuwenhoek, 1675. (63) Dobell, 1932, p. 55. (64) Van Leeuwenhoek, 1808, p. 303. (65) These illustrations, with many others, are to be found on the van Leeuwenhoek web page. (66) Steno, 1659, trans. Ziggelaar, 1997, p. 159–160. (67) The Chaos Manuscript (Steno, 1659) is so called because, under the dedication In nomine Jesu at the top of the first page, Stensen has written “Chaos,” presumably referring to the eclectic unsystematic nature of the contents. A Latin/English transcription was published by Ziggelaar, 1997. (68) Boerhaave writes that Swammerdam and Stensen lived together in the same house in Paris “in utmost intimacy” (quoted in Schulte, 1968, p. 37).

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Experiment and Observation (69) Stensen’s crisis of faith was long in coming. For many years he had been under the influence of Descartes and Spinoza. In Italy, however, he had come into contact with an elderly nun of simple faith, as well as pursuing more intellectual discussions with Lavinia Arnolfini and Father Savignani. His ultimate conversion reminds one of Blaise Pascal. He writes that “Human proofs are to no purpose.…The divine assurance can only be understood by those who have experienced it. Praised be his name who led me from darkness into light, from death to life” (Hansen, 2000, letter 73; quoted Kermit, 2003, p. 52). (70) The chronology of Stensen’s life is not easy to establish. In this short account I have drawn on various sources, but in particular the Dictionary of Scientific Biography and Hans Kermit’s recent (2003) biography. (71) Quoted, Kardel, 1994a, p. 23. (72) Both published in English translation in Kardel, 1994b. See also Bastholm, 1950 and 1968. (73) Kardel, 1994a, p. 31, 41. Stensen was working on this theory when he arrived in Florence in 1666. Borelli was in residence and was also working on his great volume De motu animalium (see Chapter 8). He did not find Stensen’s competition easy to take. (74) Steno, 1667. (75) Steno, 1669. Stensen’s lecture was translated into Latin and English soon after it was delivered and was to be found in anatomical textbooks for many years afterwards. An English translation may be found in Gotfredsen, 1950. (76) Ibid. (77) Quoted by Kermit, 2003, pp. 97–98. (78) Anon., 1669. (79) Van Leeuwenhoek, 1798: trans. Hoole S.

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Theory and Argument

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Theory and Argument C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0008

Abstract and Keywords This chapter identifies four attempts to create a successor theory and to accept the new findings of experiment and microscopy during the 17th century. It first studies Francis Glisson, who is known for his work on rickets and his research on the true function of the liver. Next, it takes a look at William Croone, who published his enquiries into the movement of skeletal muscle in De ratione motus musculorum, and Giovanni Borelli, whose intromechanics can be related to the physiology of the animal spirit. The chapter ends with a discussion on Thomas Willis, whose Cerebri anatome is considered by some to be the foundation work of neurology. Keywords:   successor theory, Francis Glisson, rickets, liver, William Croone, skeletal muscle, Giovanni Borelli, intromechanics, Thomas Willis, neurology

It is, however, necessary to add reasoning to observation. Leibniz: Letter to Huyghens, February 1691

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Theory and Argument We saw in Chapter 7 how observational and experimental techniques had cast doubt on the ancient animal spirit doctrine. Van Leeuwenhoek’s microscopy had shown that nerves were in no way tubular as Descartes had taught, and Swammerdam’s experiments had cast inescapable doubt on the old idea that animal spirit flowed down hollow nerves to activate the muscles. It has to be remembered, however, that although he had demonstrated his frog muscle-nerve experiment to all who would come, his experiments were not printed and published until Boerhaave undertook that task in 1737. Nevertheless, biomedical scientists in the 17th century, le grand siècle as the French call it, found themselves in considerable difficulty. It was not only, as we noted in the introduction to this section, that “new philosophie calls all in doubt,” but also that close inspection, including microscopic inspection, of the living body and its anatomy, could not be reconciled with prevailing biomedical theory. Something had to give. The findings of experiment and microscope seemed indisputable. But what could replace the old physiology? A similar problem had appeared before in physics and astronomy. The Ptolemaic astronomy of the Middle Ages was doomed by Copernican heliocentrism and Aristotelian physics met a similar nemesis in Galileo. Nevertheless, the old physics and astronomy, particularly the latter, did not go easily. Like the other sciences, they were deeply connected with the overarching theological worldview. Cut them away and rethink them and the old religious consensus would come tumbling down. This at least was the view of the Roman Church when it summoned Galileo to Rome in 1632 and showed him the instruments. In biomedicine the situation was not so sharply focused. The old dispensation was being progressively shown to be erroneous, but nothing comparable to the Copernican theory was as yet available to replace it. Much later, towards the end of the 19th century, Matthew Arnold, in a famous poem, likened the old theological worldview to the full tide lapping the pebbles of Dover beach, but now, he wrote, standing before his bedroom window and watching the waters ebb, all we hear is “its melancholy long withdrawing roar.” This could well provide a metaphor for the slow demise of the ancient animal spirit doctrine. What could replace the old idea? The 17th century saw numerous attempts to come to terms with the new findings of experiment and microscopy, numerous attempts to formulate a successor theory to the time-honored theories of previous centuries. In this chapter we shall review four. We start with Francis Glisson, move on to William Croone, then to Giovanni Borelli, and end with the great Oxford physician and scientist who coined the term neurology1 and inaugurated the discipline of physiological psychology: Thomas Willis. These investigators are, of course, only the best known of a cohort of physicians and natural philosophers attempting to understand the implications of the new findings for the old animal spirit doctrine.

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Theory and Argument We should not end this introductory section, however, without mentioning John Mayow (1643–1679), whose theory of nitro-aerial particles, a very material substitute for animal spirit, was published in 1674 as De motu musculari et spiritibus animalibus. Mayow’s work seems to have fallen, stillborn, from the press, for it was hardly cited until 1790, after the discovery of oxygen, Thomas Beddoes wrote that he was astonished to find that similar chemical ideas had been proposed, in a more primitive vocabulary, 100 years earlier.2 Mayow is, however, more properly regarded as a significant figure in the history of respiratory physiology rather than in the history of neuromuscular physiology, and we shall accordingly leave him to one side. Nevertheless, he stands out from the cohort of figures whom we have no space to consider in this chapter. We shall discuss his work again in Chapter 11 in connection with 18th-century theories of irritability. (p.128)

Francis Glisson (1597–1677) Francis Glisson (Fig. 8.1) was born in Dorset in 1597, and thus grew up in the last years of Queen Elizabeth’s reign and the first of her successor’s, James I of England (VI of Scotland). He went up to Cambridge in 1617 and graduated with an MA in 1624, following this with an MA at Oxford in 1627 and, finally, an MD from Cambridge in 1634. Two years later he was appointed to the Regius Chair in Physic at Cambridge, which he retained until his death in 1677. However, he spent so little time in Cambridge that he was eventually enjoined to appoint an assistant to take on his teaching and other duties. Instead of Cambridge, he gravitated first to Colchester and then, after the Parliamentary siege, to London,

Figure 8.1: Francis Glisson. (Courtesy of Wellcome Library)

where he established a successful medical practice. Here he joined the circle of savants, the so-called Invisible College, which was later, in 1662, to be constituted as the Royal Society.

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Theory and Argument Glisson is remembered first for his work on rickets, resulting in the publication of Derachtide in 1650 and then, and more importantly, on the liver, resulting in the publication of another monograph, Anatomia hepatis, in 1654. He lived through the violent years of the English Civil War and like his slightly older contemporary, William Harvey, chose the Royalist side of the struggle. They were both London physicians and Fellows of the College of Physicians. Glisson was a strong supporter of Harvey’s circulation theory and realized that it destroyed the old idea that the liver was the source of the venous system. It seems likely that part of the motivation for his great study of this organ lay in an attempt to discover its true function. In this study Glisson described, among many other structures, the fibrous capsule of the liver, which is still known to today’s medical students as Glisson’s capsule. But, far more importantly for us in this book, he also noted how the gallbladder and bile duct are activated by mechanical stimuli. This led him into a study of “irritability,” a concept that in the hands of Albrecht von Haller in the next century would become of great importance. Irritability is, in its way, a successor concept to the notion of animal spirit. We shall discuss this concept, and Glisson’s work on the gallbladder, in detail in Chapter 11. He followed up his research on the liver and gallbladder with investigations of the stomach and intestines, resulting in a further treatise, Tractatus de ventriculo et intestinalis (Treatise on the Stomach and Intestines), which was completed in 1662, although only published posthumously in the year of his death, 1677. Here, again, the concept of “irritability” looms large. Between writing and publishing this latter volume, Glisson published a large metaphysical tract, Tractatus de natura substantiae energetica (1672), in which he sought to replace Descartes’ materialistic philosophy with a vitalistic theory.3 Matter, he argued, was not inert but imbued from the first with vital properties. All matter, he maintained, was both perceptive and inherently motile.4 The concept of irritability followed naturally from this philosophy. As it became an important concept in the following century, and as it was, in a sense, a successor concept to the doctrine of animal spirit, it is worth spending a little time on it. More detail will be found in Chapter 11.

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Theory and Argument Glisson distinguished sensation and perception. The former depended on the brain, the latter was an inherent property of all matter, including, of course, living matter. Tissues, such as the gallbladder or the wall of the intestine, reacted spontaneously to touch or other stimulus. They must thus be able to perceive that stimulus. Not only must they be able to perceive the stimulus, they must also be able to react. They must, in other words, possess motive power. This dual property of perception and motive response defined, for Glisson, the notion of irritability. Irritability is, moreover, as he argued in his philosophical treatise, inherent in the very elements of which the tissues are constructed. These elements were, in Glisson’s view, “fibers”; they were, for Glisson, like atoms were for 19th-century physicists, “hypothetical” entities. Just as, before Einstein, physicists regarded “atoms” very much as Democritus had regarded them, as useful theoretical constructs but not necessarily having any observational reality, so Glisson and many of his successors regarded fibers as theoretical entities from which the anatomy was woven. The fiber concept remained in anatomy until Schleiden and Schwann established cell theory in the middle of the 19th century. Irritability, being an inherent property of the fibers of which the body was composed, was, nevertheless, controllable by the nervous system. Fibers would react spontaneously to external stimuli (natural perception), but they would also (p.129) react in response to messages transmitted by the nerves from the brain. There were two cases. First, sensory perception. Fibers could respond “automatically” to sensory input. This is an early description of “reflex” response: as, to take Descartes’ example, when the muscles controlling the eyelids respond automatically to the sight of a raised fist. Second, the fibers could be caused to respond by conscious intention, or “will.” Glisson does not discuss how the nerves activate the fibers in either of these two cases. Perhaps he is content to leave argument about animal spirit to others. But he did refer to one significant experiment that put in question the Cartesian theory of muscle contraction. This experiment, often ascribed to Glisson but actually performed by Jonathan Goddard (1617–1675) before the Royal Society in 1669, was designed, like that of Swammerdam’s (Chapter 7), to determine whether a muscle really did “balloon” (that is, increase in volume) when it contracted. Goddard’s experiment did not require the delicate glass apparatus that Swammerdam devised. Instead, he asked that a subject immerse his arm in a tube of water, with a glass pipe sealed at the distal end, and flex his biceps muscle. He showed that no water was displaced, the level remaining much the same (Fig. 8.2). He concluded that the Cartesian idea that muscle contraction was due to an influx of animal spirit could not be correct.5

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Theory and Argument Glisson’s conclusion was, however, far from being universally accepted. He was, we noted above, a member of the circle of natural philosophers, which was later to become the Royal Society. In the early 1660s when this Society was being formally constituted, there was a great deal of interest in the forces that the inflation of animal bladders could deliver. John Wilkins (1614–1672), for instance, had performed a whole series of experiments in which he showed that it was possible to raise a weight by blowing into an empty bladder. Several other experiments of the same type were performed at about this time.6 Moreover, the interest in the inflation of bladders to lift weights was not confined to England. In Nuremberg, for instance, a number of experiments elaborating on those of Wilkins were devised (Fig. 8.3A–C). Accounts were published in 1676 in the second part of Collegium experimentale sive curiosum.7 Clearly, if these experiments were to be taken as an explanation of muscular contraction, they went against the demonstrations of Goddard (and Swammerdam) that muscles did not increase in volume during contraction. Rather, they supported Descartes’ view that muscles contracted due to inflation caused by an influx of animal spirits. Yet there was gathering evidence that nerves were not the hollow tubes required by Cartesian theory, and that muscles contained no cavities that could be inflated. What could be going on? There was a huge disconnect between theory and observation; something else must be happening. Both William Croone and Giovanni Borelli, whom we consider next, sought to explain what this “something else” was.

William Croone (1633–1684) William Croone (Fig. 8.4) was born in London in 1633 and went up to Cambridge in 1647, where he took a degree in arts. In 1659 he was appointed Professor of Rhetoric at Gresham College in London. Here, like the other figures mentioned in this chapter and the previous one, he was much involved in the Invisible College of savants that was later, with the restoration of Charles II, to become the Royal Society. When this happened in 1662, he was elected their first Registrar. Although having no medical education, he was nevertheless created Doctor of Medicine at Cambridge in 1662 by royal mandate and in 1675 admitted as Fellow of the College of Physicians. In 1670 he was appointed lecturer on the anatomy of muscles at the Company of Surgeons, and he held this position until his death in 1684. He became a highly successful physician in London, “very lively and active and remarkably diligent in his enquiries.”8 It is to those enquiries and in particular his enquiries into the contraction of muscle that we now turn. Croone published his enquiries into the movement of skeletal muscle in a small treatise published in 1664, De ratione motus musculorum.9 In many ways this is a work

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Theory and Argument (p.130)

Figure 8.2: Goddard’s experiment (see text). (From Birch: History of the Royal Society, vol. 2, p. 412)

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Theory and Argument of synthesis. He based his hypothesis on the work of many famous predecessors: Fabricius, Fallopius, Harvey, and, especially, Descartes. But it is far more than a review of the work of his predecessors and contemporaries. It is also based on experiment and suggests further experiments. If the latter do not support his theory, then, says Croone, it should be rejected.

The motif underlying Croone’s work has to do with bladders and their filling and emptying. This, as we noted above, was of much interest to physiologists in the first part of the 17th

Figure 8.3: Lifting devices from Sturm, JC (1676–85): Collegium experimentale sive curiosum. (A) Lifting a weight with a

single bladder. M: leather flap to prevent century. We saw in Chapter 6 backflow of air; P: base of bladder; Q: how Descartes accounted for hook; R: weight (36 lb). (B) Lifting a muscular contraction by weight of 150 lb by a series of four arguing that animal spirits bladders. PQR: rope linking bladder flowed down motor nerves and, series to lever; S: fulcrum; TVX: rope by an intricate arrangement of connecting lever to pulley system; XY: valves, caused the inflation and pulley system; Z: 150-lb weight. (C) deflation of agonist and Lifting a circular weight by inflating eight antagonist muscle pairs. attached bladders. Eight “robust youths” Croone, however, as the were to be employed in inflating the Surgeon’s lecturer on the bladders. anatomy of muscles, asks: where are the cavities in skeletal muscles? Where are the valves in the nerves? They are, he asserts, nowhere to be found. Nevertheless, he makes use of Descartes’ analogy of the human body to an automaton. “Let us consider,” he writes, “the body of a living creature to be nothing else than a sort of machine or an automaton and let us, for a while, banish the mind which is in us”10—almost word for word from the first paragraph of Descartes’ L’Homme! But he does not, as did the great Frenchman, devise a completely imaginary neurophysiology. His theory is far closer to the best available anatomical knowledge. Nevertheless, it contains much speculation, non-testable at the time. He suggests, like Swammerdam (Chapter 7), that sensation is delivered to the (p.131)

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Theory and Argument brain by percussive transmission along the taut membranes of sensory nerves. They are capable, he writes, of vibrating “like a bell or as the purest glass,” if struck, and this vibration is transmitted to the brain.11 Similar though, as we shall see, far subtler ideas were popularized in the next century by Isaac Newton and more extensively by David Hartley.

But he does not follow Swammerdam in banishing animal spirit from his physiology altogether. If sensory nerves conducted their messages from the periphery to the central nervous system by a percussive mechanism, motor nerves still exerted control over the muscles by animal spirit. This spirit is distilled from the blood. He does not make clear Figure 8.4: William Croone by Mary where or how this process Beale about 1680, when Croone was 47. occurs, but we can assume he From Royal College of Physicians, accepts some form of the London. (‹old, rcplondon.ac.uk/historytraditional theory. But it risks heritage/Collge-history-new/Historicalsharing the same fate as lectures/Pages/Croonian-(SadleirHarvey’s vital spirit. In some Trust).aspx›) passages he writes that it is no more than the vapor, the “bouquet,” of the medullary substance in the nerves (we might identify this “medullary substance” with our axoplasm). In other places, and more frequently, he takes this medullary substance to be the animal spirit itself: “a very rich spirituous juice which is drawn through all the nerves in a constant circuit…this liquor itself, or animal spirit, is driven out of the branches of the nerves by the violent movement of the (muscle) fibers.”12 He also writes that this “very rich spirituous juice” has a nutritive as well as physiological function. Like Glisson before him he had noted that a denervated muscle atrophied, even though the blood supply remained uninterrupted.

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Theory and Argument Croone’s account of animal spirit is clearly somewhat equivocal. Is it to be identified with the succus nerveus itself or with its “bouquet”? He oscillates. It has to be remembered, moreover, that unlike Harvey’s blood, the succus nerveus was more a theoretical construct than an observable substance. Ultimately the spirit escapes from the muscles and percolates through the entire anatomy to be collected by the veins for recycling. Croone’s understanding here is that the nerves innervating a muscle branch and branch again until they disappear into the substance of the muscle. The “very rich spirituous juice,” the animal spirit, is drawn into the muscles, where it interacts with the spirits of the blood already there, causing “a great agitation of all the spirituous particles…as when spirit of wine is mixed with spirit of human blood.”13 This is where the analogy to the inflation of balloons is made. Croone suggests that, below the level of visibility, the muscle contains a vast number of tiny globules laid end to end. He devises a geometrical analogy (Fig. 8.5). He argues that the fine structure of muscle might be compared to a series of rhombs joined end to end. When the area of each rhomb increases toward a maximum, they will tend toward squares and hence the whole line will shorten.14 Croone does not, of course, require the microstructure of muscle to consist of rigid rhombs as in his geometrical analogy. Inflatable globules would do just as well—or better—and we noted in Chapter 7 that, in 1678, Robert Hooke, in time for the 1681 (second) edition of De ratione motus musculorum,15 believed that he had found microscopic evidence for just such a fine structure. Van Leeuwenhoek, moreover, was also at that time a convinced globularist. In a letter published by the Royal Society in 1674, he writes that, having many times dissected the fine carneous filaments from the flesh of a cow (“25 times thinner and finer than a hair”), “I saw to my wonder that they were made up of very fine conjoined Globuls.” Three years later, in 1677, in response to a request from the Royal Society, he writes again that “I have always found, that they consist of such parts, to which I can give no other figure than globular.”16 Thus, for William Croone, contraction is caused by the will directing both blood and succus nerveus to a muscle, leading to an instant ebullition (p.132)

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Theory and Argument within the cavities of the myriad tiny globules.17 The muscle expands in girth and contracts in length. We shall see in the next section that a very similar, though more thoroughly worked-out mathematical theory, was developed by Borelli.

But how does Croone reconcile his theory with Goddard’s demonstration that muscles do not expand like balloons when they contract but retain very much the same volume? He is equivocal. He says that there is an increase in volume, though comparatively slight. The solution to this conundrum was slow in coming. Indeed, it did not truly arrive until the slidingfilament biochemistry of muscular contraction was worked out in the 20th century. It is interesting to note, however, that Stensen’s tentative parallelepiped mechanism (discussed in Chapter 7), although entirely theoretical and not at the microscopic level, points toward our present understanding.

Figure 8.5: Croone’s geometric analysis of muscle contraction. (i) The set of four rhombs have, as squares, maximum area (or, if cubes, maximum volume). (ii) The rhombs no longer have maximum area (or volume).The weight (w) consequently moves up or down. (After Croone, Philosophical Collections 2, 1681, Fig. 3)

In Croone’s theory animal spirit does not have quite the same inanimate nature as in Descartes’ hydrodynamic physiology. It has a much more biological flavor, influenced perhaps by Glisson’s vitalism. On the other hand, it no longer carries the Scholastic, mentalistic, baggage of medieval psychophysiology. It oscillates, in Croone’s mind, between, as we noted, a bouquet or aroma given off by the succus nerveus within the nerve tubes and the succus nerveus or nerve “juice” itself. In both cases it can be seen that Croone’s vision is far less mechanistic than Descartes’. In the end, however, Croone admits that the causes of muscular movement must remain mysterious. He writes that he is “almost persuaded [that] no Man ever did or will be able to explicate this or any other Phenomenon in Nature’s true way and method.”18

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Theory and Argument Giovanni Borelli (1608–1679) If early- and mid-17th-century England was driven by the violence of Civil War and the death, restoration and flight of monarchs, Italy was hardly, if at all, more propitious for the calm pursuit of scientific research. The old religion had far deeper roots in Italy than in the countries across the Alps in northwest Europe. When Stensen visited Livorno in 1666, he saw bystanders drop to their knees as the consecrated bread and wine were carried through the streets. Transubstantiation was not merely symbolic but the literal truth. In 1633 Galileo had been summoned to Rome (with the alternative of being transported in chains) for his crucial encounter with the Holy Office. If Descartes in faraway Amsterdam felt threatened, how much more at risk must the upcoming generation of scientists in Italy have felt! Italy, too, was far from unified. It was politically fragmented, divided into a number of small states, of which Tuscany was by far the largest. The Spanish retained military control of the south; in particular, they garrisoned three military forts in Naples. It was into this troubled society that in January 1608 Giovanni Borelli (Fig. 8.6) was born and grew up. He first saw the light of day in Castel Nuovo, a village on the outskirts of Naples, the first son of a Spanish infantryman and Laura Porello, a local woman. He took his mother’s name, corrupted to Borelli. Some time in the late 1620s or early 1630s, he traveled from Naples to Rome, where he became a student of Benedetto Castelli (1578–1643), Professor of Mathematics and close friend and supporter of Galileo. It follows that the young Borelli must have been very aware of the swirling currents of scientific and religious argument surrounding the trial and condemnation of the great Pisan. In 1635, at the recommendation of Castelli, Borelli obtained a lectureship in mathematics in Messina, Sicily. Twenty-one years later, in 1656, at the second attempt, he obtained the Chair in Mathematics in Pisa. It was here that, as we noted in Chapter 7, he met Marcello Malpighi and together they took part in the development of the short-lived Accademia del Cimento. This was not the first or the only scientific group that Borelli helped to set up. While in Messina, he had been involved in setting up the Accademia della Fucina (Academy of the Forge), which became a center not only of scientific but also political discussion. He was also in touch with the group of natural philosophers centered on his birthplace, Naples, which in 1663 became the (p.133)

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Theory and Argument Accademia degli Investiganti. But it is his collaboration with Malpighi that is of most interest to us here, and we shall return to it below.

Borelli remained in Pisa for 11 years until, in 1667, he set out for Sicily once again, stopping off in Naples to exhibit some of his experimental work to the Investiganti and arriving in Messina in 1668. Once back in Sicily, he continued his scientific investigations and rejoined the Fucina. He began to take a yet more active part in politics. The citizens of Messina had started to grow weary of their Spanish overlords. The Spanish reacted in 1672 by burning the house in which the Fucina, regarded as the source Figure 8.6: Giovanni Borelli. A sketch by of the discontent, met, Leone Ghezzi, when Borelli was in his destroying many of its early 50s, about 1658. (See Middleton, documents. Borelli was 1974) declared persona non grata and a price set on his head. Two years later, 1674, the simmering revolt broke into the open and fighting continued, off and on, until 1678. But Borelli had long gone. Discretion being the better part of valor, he had fled back to Rome. There, like René Descartes, he came to the attention of and received the patronage of Christina, ex-Queen of Sweden. Christina was interested in organizing scientific meeting groups and in 1674 inaugurated the Accademia Reale and was also involved in the Accademia Fisica-mathematica, to both of which Borelli contributed. Borelli was by now well on in years and he lacked financial resources, especially after a servant robbed him of all his possessions. He was reduced to teaching elementary mathematics at the Casa di St. Pantaleo, which also provided bed and board. He was now entering his 70s and failing fast. He was mostly concerned to see his great work, De motu animalium, through the press. In 1679 Christina agreed to defray the printing costs and Borelli accordingly dedicated his masterwork to her. He died in December of that year and the Casa di St. Pantaleo, in which he had spent his last days, took over the task of seeing that De motu animalium was finally published.19 Page 13 of 31

Theory and Argument Let us now return to 1656 and to Borelli’s meeting with Malpighi in Pisa. Malpighi was 28 and a rising star in the biomedical world. His talents had been recognized by his appointment to a Chair of Theoretical Medicine. Borelli, as we have seen, was in his late 40s, 20 years older than the new professor and widely experienced both in the physical sciences and in politics. But almost immediately after he had taken up his Chair in Mathematics, he set up and equipped an anatomical laboratory in his own house. Malpighi must have visited and advised. As we noted in Chapter 7, he is often regarded as the founding father of animal histology and he was also fascinated by the fine structure of the brain. We can imagine the two new professors, one in medicine, the other in mathematics, bending over their simple equipment and arguing about what the microscope revealed. Malpighi writes: “What progress I have made in philosophizing stems from Borelli. On the other hand, dissecting live animals at his home and observing their parts, I worked hard to satisfy his very keen curiosity.”20 Malpighi brought the problems posed by animal movement to Borelli’s attention,21 and the latter’s great book De motu animalium makes many references to his friend. Their talents were to an extent complementary: Malpighi, the anatomist and microscopist, attempting to make biological sense of the structure his microscope revealed (or seemed to reveal); Borelli, the mathematician and physicist, attempting to cast Malipighi’s microscopic images into a physicomathematical framework. It might be argued that, from this fruitful Pisan collaboration, two great sciences emerged: neurohistology and biophysics or, as the latter was then called, “iatrophysics” or, better, “iatromechanics.” We have already reviewed Malpighi’s neurohistology. Here we shall say something of Borelli’s iatromechanics and its relation to the age-old physiology of animal spirit. Borelli’s great book on animal movement begins with an extensive discussion of the mechanics of muscular movement, focusing, in particular, on the movement of joints, their comparison with levers, the forces that can be exerted, and the various gaits of men and other animals: running, jumping, skating; the flight of birds; the swimming of fish, etc. He then moves on to a consideration of the muscles themselves. But before he does that, he makes a careful mathematical analysis of the forces involved in the movement of single and multiple rhomboids. This analysis, as with his earlier comparison of the jointed skeleton with levers and the gait of animals, is illustrated by beautifully drawn diagrams (Fig. 8.7). (p.134)

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Theory and Argument Following this geometrical analysis, he goes on, after showing that the comparison of muscle contraction with the contraction of a wetted rope makes no sense,22 to argue, in Proposition CCIV of Volume 1, that, “Any muscular fiber is similar to a chain of many rhombs.” These rhombs, he continues, “are rather similar to rhombs made of threads tied together, which are widened by a motive faculty and thus contract.” We have, of course, come across this idea earlier in this chapter in William Croone’s 1664 Motus musculorum. There is really no dispute over priority. Although Borelli did not publish his great work until 1680/81, he was at work on it many years earlier. Croone admits that he saw a few preliminary pages of Borelli’s De motu when he was putting together the 1681 (second) edition of Motus musculorum, but not the whole work.

Figure 8.7: Table IX from De motu animalium.

Borelli goes on in succeeding propositions to elaborate his iatromechanics. He writes (Proposition CXV) that “muscular fibers are thinner than female hair” and the row of rhombs it contains is such that “a series of 50 of them does not exceed one finger breadth.” He follows this in his next proposition (Proposition CXVI) by arguing that contraction and swelling of a fibrous column can only be conceived if the transverse diameters of the pores increase and their longitudinal diameters decrease…the small machines or swollen segments of one fiber must be adjacent to other small machines similarly contracted and they must constitute the same texture as a fascicular network made of small rhomboidal machines.

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Theory and Argument He continues with extensive analyses of the force generated by his muscle machine and by a discussion of how this might be applied in the gait of humans and other animals. But what is it that causes the rhombs to expand to their maximal area or, in three dimensions, volume?23 Borelli’s answer to this question is to be found in the second volume of his masterpiece. He starts by dismissing the opinions of those who would rather listen to the teachings of Aristotle than to those of nature. He also scorns the opinion, which he attributes to Galen, that muscular movement is caused by the transmission of an immaterial faculty: “the tridimensional mass of a muscle cannot be increased and swollen by an immaterial faculty which has no dimension like an indivisible point” (Proposition XVI). Nor, he continues in the next proposition, can it be animal spirits (“very small bodies like gas”), for if muscles in a live animal are incised longitudinally and caused to contract under water “no stream of bubbles is ever observed to ascend from them.” He goes on to eliminate various other possibilities before presenting his own solution. This solution is given in Propositions XXII to XXIX. In essence, Borelli argues that the contraction of muscles requires two causes: one (he says) is present in the muscle itself and the other is external and delivered to the muscle. The external cause is transmitted through the nerves. This, and he is adamant, is not some “immaterial faculty or…airy spirits” but “some material substance.” When this material substance, this “nerve juice,” reaches the muscle it interacts with something in the muscle and this results “in something which, like a fermentation or an ebullition, produces…instantaneous contraction of the muscle.” But what is sent through the nerve, and with what does it interact in the muscle? A nerve, he says, and here he may have benefited from Malpighi’s microscopy, is composed of minute fibers and these fibers, “like the veins of fleas,” although too small to be seen, may well be hollow tubes, full, he says, of a spongy, wet substance like the “marrow of elder, giant fennel or sugar cane.” This spongy substance, or nerve juice, fills the nerve fibers to turgescence and “a jolt or irritation” at one end causes the expulsion of “some drops” at the other end into the “fleshy mass of the muscle.”

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Theory and Argument He goes on to insist that “it seems unquestionable that animal spirit is a fluid, very delicate, extremely pure and mobile substance.” It cannot produce effervescence and/or (p.135) turgescence in itself, else this would happen in the nerve fibers: and it doesn’t. The distal orifices of the nerve fibers are scattered throughout the mass of a muscle and, when the succus nerveus is expelled, it interacts with something already in the muscle. This, he concludes, is either lymph or blood. A consideration of the chemistry of blood leads him to believe that this is the “something” with which the succus nerveus interacts. He gives many analogies, including the way in which “sparks retained in the structure of rock” may escape when struck by steel and “the cold ebullition” resulting from “dissolving ammonia salts in oil of vitriol.” Taken together with his rhomboidal muscle microstructure, we can see how muscle contraction is brought about. Borelli’s neurophysiology also includes a theory of how messages are sent from the periphery to the brain. When a sense organ is stimulated, he writes, the percussive force leads to “spirituous juices” being extruded in “the sensitive area of the brain.” He totally rejects the notion that sensory information is sent by a vibratory mechanism along tense fibers or their membranes: the nerves, he says, are not rigid, like zither strings or iron rods, but soft and loose, like a folded thread of cotton. But a problem arises: how can transmission occur in both directions? A piece of rhubarb, he says, is rejected from the mouth at the same time as its bitterness is sensed; similarly, the pain felt by a muscle cut by a sword seems to occur at the same moment as it contracts. Borelli has two answers (Proposition CLVII): first, that different fibrils within the nerve are specialized to conduct in one direction only, either inwards or outwards; second, and he says more likely, the same fibril conducts in both directions, inwards and outwards, but the alternation of opposite movements is so rapid that they cannot be distinguished. Finally, Borelli agrees with his British colleagues, Glisson and Croone, that the succus nerveus has two functions: nutritive and motive. But he thinks that the “nutritive nervous juice” is different from the “nervous juice” of the motive and sensitive spirits. The spirits of the nutritive juice, he writes (Proposition CLVIII), “are very sweet, inducing quiet sleep” while the animal spirits are “most noble, bitter, sulphurous, saline and very active, like spirit of wine.”

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Theory and Argument Here we must leave Giovanni Borelli. We can see in his analyses glimmerings of a neurophysiology acceptable today. But it is a neurophysiology of the 17th century. Although his mathematical and logical reasoning, his series of propositions, his resort to experiment, are all truly Baconian, he is necessarily restricted by the scientific instruments of the time. Without the benefit of achromatic compound microscopes and the appropriate preparative equipment and histological stains, etc., his knowledge of the fine structure of muscle and nerve was bound to be limited; without the benefit of several hundred further years of chemistry and, latterly, biochemistry, he could go no further. The analogies by which he attempts to explain muscle movement are taken from life in 17th-century Italy. They are insightful and helpful, but often insightful and helpful in pointing him in the wrong direction. Settle, in his 1970 biography, regrets that Borelli lived in the Italy of the Counter-reformation, where science was practiced against the grain of the dominant culture. Borelli, he believes, could have been an even greater star of the 17th century had he lived in a more free-thinking environment.

Thomas Willis (1621–1675) Thomas Willis is the last of the great 17th-century physicians and natural philosophers to be considered in this chapter (Fig. 8.8). He was born in January 1621 at Great Bedwin in Wiltshire, the son of an Oxfordshire farmer. He was educated at Oxford during the Civil War. His family were strong Royalists and not only did the young Thomas join the university legion to defend the city, but his father died, probably from typhus, while in the besieged city. Due to these wartime excitements the young Willis received very little in the way of formal training in medicine. Indeed, it is likely that he spent no more than 6 months attending classes. It has been argued that this, far from being a drawback, was a considerable advantage. The young Willis was spared the 3 years of largely literary study that then constituted the Oxford curriculum; he was free to read for himself, experiment, and come to his own conclusions.24 At first Willis’s medical practice was small. He was left with plenty of time to work at his own interests. These included

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Theory and Argument (p.136) not only anatomy but also, and importantly, iatrochemistry. Aubrey, who knew him well at this time, called him “our chymist” and he became an active member of the small “Oxford Philosophical Clubbe,” which had set up a laboratory at Wadham College. At this time Willis had several collaborators and assistants in his chemical experimentation. These included the young Robert Hooke, Richard Lower (1631–1691), William Petty (1623–1687), and Robert Boyle (1627–1691). They were known as the Oxford “Sparkles.” Later, with others, they formed the nucleus of the Royal Society in London. It was at this time also, in December 1650, that one of the defining events in Willis’s career occurred. Ann Green, who had been convicted of infanticide, was led to be executed by hanging. The story

Figure 8.8: Thomas Willis. Engraving by G. Vertue, 1742, after a portrait by D. Logan, c. 1666, when Willis was 45.

is well known.25 After half an hour (‹http://www.britannica.com/EBchecked/ or so she was pronounced dead media/33103/Thomas-Willis-engraving-byand taken down from the gallows. G-vertue-1742-after-a-portrait›) Her body was taken to Petty’s lodgings for postmortem examination and dissection. When Petty and Willis opened the coffin they heard her breathing and were able to resuscitate her. She made a full recovery, was pardoned of her crime, and lived many years, marrying and bearing three children. This remarkable event brought Willis to the notice of the medical world.

In addition to this much-talked-of resuscitation, Willis began to publish. His first book, Diatribe duae medico-philosophicae (Two Medico-Philosophical Arguments —one on fermentation, one on fevers) was published in 1659. In 1660, after the Restoration of the Monarchy, his success as a physician and anatomist, and perhaps also his services in the Royalist cause, were recognized by appointment to the Sedleian Chair in natural philosophy at Oxford. In the same year he was created Doctor of Medicine. But perhaps most importantly for us, in 1664 he published his great work, taken by some to be the foundation work of neurology, Cerebri anatome.

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Theory and Argument In 1667 Gilbert Sheldon, the Archbishop of Canterbury, asked Willis to leave Oxford for London. Willis, always a devout believer, could not refuse, and although he did not give up his Oxford Chair, quickly established a very successful practice in the metropolis. In the same year he published Pathologiae cerebri, et nervosi generis specimen (Cases of Brain and Nerve Pathology). Three years later, in 1670, he was formally admitted as a Fellow of the Royal Society (although he had been unofficially a Fellow since its foundation in 1662) and went on to publish his other great work, this time on physiological psychology, De anima brutorum (1672).26 Willis had only another 3 years to live. Perhaps the smoky atmosphere of the great city where he worked without surcease led to his last illness, pneumonia, from which he died at the age of 54 in November 1675. According to his friend John Fell, who was with him in his last hours, “he took holy communion, commended his pious soul to God, having his senses entire to the last breath and finished his most exemplary life with the like breath.”27 Willis was of medium build and of no great presence. He seems to have been somewhat withdrawn, perhaps because of numerous family bereavements, and is reputed to have had little small talk. He seldom attended the meetings of the Royal Society, preferring to learn of their discourses second-hand. This may well have been because of his extreme workload, which started with early-morning prayers, followed by consultations with those of modest means in his house and then visiting the well-to-do by carriage. He has been accused of allowing others to make his anatomies, but this seems not to have been the case. He always seems to have been primus inter pares in the dissecting room. Nevertheless, the accusation that he tended to be seduced into “framing theories” rather than in “busying himself in observations and experiment”28 seems to have substance, and was certainly very generally made by his contemporaries. We saw in the last chapter how Niels Stensen, while admiring the Wren drawings in Cerebri anatome as the best available (Fig. 8.9), nonetheless despaired of Willis’s theoretical cast of mind. In his defense Willis argued that his anatomical studies were intended as a foundation for higher things: “a necessary springboard for a rational understanding of nature, mind and disease,”29 and in the dedication to Cerebri anatome he writes that the study of anatomy “can unlock the secret places of Man’s Mind and look into the living and breathing Chapel of the Deity.”

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Theory and Argument (p.137) With Thomas Willis in contrast to Giovanni Borelli and the other investigators discussed in this chapter, we feel we are in the presence of a genuine neuroanatomist. He was, moreover, not afraid to admit and praise the help of others. His great work on the anatomy of the brain and nerves is, he is happy to say, not his alone but the collaborative work of several—in particular Richard Lower, Thomas Millington, and Christopher Wren. It is the outcome of discussion and, in particular, graced by the skilful draftsmanship of Wren; for to “explicate the uses of the Brain” he says, “is as difficult a task as to paint the Soul.”30

Figure 8.9: Sir Christopher Wren’s drawing of the base of the human brain, showing the arterial circle now known as the circle of Willis, from Willis’s Cerebri anatome (1664).

His account of the brain is thus directed throughout to its functioning. Throughout his anatomy he attempts to make sense of its functioning in terms of animal spirits. This, he acknowledges in his preface, is no easy matter. For, he writes. “They can in nowise be seen.” He takes the conventional, time-honored position that they are distilled from the blood coursing through the multitudinous vessels of the brain (our cerebrum) and cerebel (our cerebellum) as if, he says, through an “Alembick.” Furthermore, it is important to note, he says, that this distillation occurs only in the cortex of the brain and the cortex of the cerebel and not throughout the central nervous system. The spirits, he writes, are formed from the highly volatile spirituous part of the blood, which naturally arrives first in the brain, having boiled up the nearvertical carotid arteries and which is then distributed in the vessels intertwined in its convolutions.

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Theory and Argument He goes on to attempt a description of these mysterious entities, the animal spirits. His account is difficult and labyrinthine. We can imagine him, as he writes in the preface to his Anatomy of the Brain and Nerves, meeting his collaborators and putting his ruminations before them for discussion, being, as he writes, “uncertain in my mind, and not trusting my own opinion.”31 Whether they tried to dissuade him from publishing them we do not know. Looking back, however, we must be grateful that they failed, for his passages in De anima brutorum show how an educated late-17th-century mind understood the meaning of the term “animal spirits.” Thus he writes that they are “most thin, invisible, and nimble” and constitute the “sensitive Soul…yet what they are according to their proper essence,” he continues, “seems hard to be unfolded; because we can hardly meet with anything in Nature, to which they may be compared in all things.”32 He continues by writing that to compare them “with Spirits of Wine, Turpentine, and Harts-Horn, and such like” is not really adequate: For besides, that those Chymical Liquors, neither represent the Images of their Objects, nor are imbued with any Elastic virtue, as the Animal spirits; these also are less Subtle than these, and less volatile…but the Animal spirits presently vanishing, after life is extinct, leave no Foot-steps of themselves. Wherefore, it is better…that we liken these spirits sent from the Flame of the Blood, to the Rays of Light. This comparison, from our 21st-century vantage point, seems far-fetched. It probably also did, as Stensen observed, to many in the 17th century. Yet, as we read on, we can see that Willis is wrestling to explain the nature of these invisible entities in terms familiar to his 17th-century readers. Thus, he says, “as Light figures the Impressions of all visible things;…so the Animal Spirits receive the impressed Images of those,…and stay them at the first Sensory.” In other words, animal spirits, like rays of light, carry images inwards and deposit them in the appropriate sensory area of the brain. He then goes on to argue that just as the Air, or Aerial particles, whilst free and unmixed, create nothing of force or tumult, yet they being more strictly pressed together, shut up in Clouds or Instruments, or imbued with Sulphureous, and other Elastick Bodies, presently become raging, they often break forth into Meteors, viz. Winds, Hurricanes, and horrid Thunder. After the same manner, the Animal Spirits, whilst pure, are carried in the open spaces of the Head, and its Appendixes, remain quiet enough; but they being shut up within the Muscles, and there being mixed with Sulphureous Particles from the Blood, and sometimes in other places, with an heterogeneous matter, become very impetuous, to wit, Elastick, or Spasmodick or Causing Cramps….33

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Theory and Argument The role of analogy and metaphor has always been crucial in brain science. In our times, we increasingly use metaphors drawn from the dominant technologies of our age: computers and information technology. In the 17th century, as we have just seen, Willis reached for metaphors from the meteorology and optics of his time. But, like us, he also makes use of images drawn from contemporary technology. “In Mechanical things,” he writes: Fire, Air, and Light, are chiefly Energetical, which humane Industry is always wont to use, for the greatly stupendious, and no less necessary works. This the Furnaces of Smiths, Chymists, and Glass-men, and of other boylers of several Kinds, Dioptrick Glasses, Musical, Warlike, Mathematical Instruments, with many other Machines, never enough to be admired, do testifie. In like manner we may believe, that the Great Workman, to wit, the Chief Creator, from the Beginning, did make the greatly active, and also the most subtil Souls of Living Creatures, out of their Particles, as the most active; to which he gave also a greater, and as it were a supernatural Virtue and Efficacy; from the Excellent structure of the Organs, most Exquisitely labored, beyond the Workmanship and artificialness of any other Machine.34 These “most active particles,” the animal spirits, he writes, distilled in the cortices or “barky substances” of the brain and cerebel, perform different functions. “Within the brain,” he writes, they are responsible for “imagination, memory, discourse, and other more superior Acts of animal Function.”35 He goes on to assign specific regions of the brain to these “superior Acts.” Stensen, as we noted in Chapter 7, took this (p.138) to be a speculation too far and chastised Willis for his temerity. Indeed, as we read on through Willis’s book, we tend to agree. Nevertheless, this impulse to localize mental faculties recurs throughout the history of brain science—most especially in the phrenology of the early 19th century and in what some have called the “Technicolor phrenology” of 21st-century neuroimaging. Willis cannot stop himself theorizing on the functions of the neuroanatomy he and his friends so carefully dissected and illustrated. But his theorizing looks back to the ideas of previous centuries. His conversations and speculations in his Oxford dissecting room must often have exasperated his more practically minded colleagues. Stensen is quite right when he remarks that, because of this excessive admixture of outdated neurophilosophy, few have made use of Willis’s work in developing future neuroscience. Like so many others in the 17th century he is Janus-faced, half in and half out of the modern world.

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Theory and Argument In contrast to the brain (our cerebrum), the cerebel (our cerebellum) is, he says, designed “for some works, wholly distinct” and different. These, he writes, have to do with involuntary activities such as the beating of the heart, respiration, “concoction of the aliment,” etc. Here he makes an easy (too easy!) transition from the physiological to the psychological. He writes that “often as we go about voluntary motion, we seem as it were to perceive within us spirits residing within the forepart of the Head to be stirred up to action, or an influx. But the spirits inhabiting the Cerebel perform unperceivedly and silently their work of nature without our knowledge or care.”36 Willis breaks with tradition in having very little to say about the brain’s ventricles. In contrast to the central role they played in the Alexandrian, Galenical, and Cartesian neurophysiology, they have no part in his neurophysiology. So far as Willis is concerned, “they are only a vacuity resulting from the folding up of its (the brain’s) exterior border.” “The Ancients,” he writes “have so magnified this Cavern, that they affirmed it as the Shop of Animal Spirits, both where they themselves were procreated, and performed the chief works of animal Function. But; on the other side, the moderns or those of later days have deemed them places so vile, that they have affirmed them to be mere sinks for carrying out the excrementitious matter.”37 Willis is contemptuous of both opinions and writes that he will say no more but pass on in silence. Instead of filling the ventricles, as Descartes and the ancients imagined, the animal spirits, according to Willis, distilled in the brain and cerebel, fill the medullary trunk “like the chest of a musical organ,” and thence find their way into the nerves and outwards to the muscles, membranes, and other parts to induce “a motive and sensitive or feeling force.”38 Once in these extremities (with which the nerves are interwoven), the spirits lie quiescent and are only activated by stimuli of one sort or another. Feelings, sensations, thus appear, for Willis, to be peripheral. The spirits pick up external impact and deliver that knowledge to the brain.

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Theory and Argument But what of the nerves themselves? Willis seems to be in two minds. In successive paragraphs he says they are and they are not hollow! They are, he says, extensions of the medullary trunk of the brain and cerebel. In one paragraph he writes that they are “not bored through as in veins and arteries… no cavity can be seen in them, no not by the help of Spectacles or a Microscope.”39 Yet in the next paragraph he writes that “the nerves themselves (as may be discovered by the help of a microcosm [sic] or perspective glass) are furnished throughout with pores and passages, as it were so many little holes in a honey-comb…the tube-like substance of them, like an Indian cane, is everywhere porous and pervious.” In the first paragraph he writes that “The spirits themselves are carried on the sides of, not within, these minute fibrils [although]…the subtil humor which is the vehicle for the spirits may…creep leisurely through.” In the second, that within these tubules, these “many little holes,” the “Animal Spirits…do very gently flow.” Which are we to believe to be Willis’s final opinion? When he came to write De anima brutorum in 1672, he writes of the animal spirits “blowing the nerves up to a certain tensity.”40 At this date, then, Willis had decided that nerves did contain hollow tubules. He goes on to assert that, in addition to the spirits, a “Vehicle,” a watery latex, is also to be found in the microscopic tubules within a nerve. This vehicle also flows, carrying the spirits gently along the tubules, and diffuses them through the whole nervous system. Not only does it carry the spirits through the system but it also holds them in place, else they would “vanish away into the air.” Moreover, the watery latex is vital for fixing and passing back to the brain “the sensible Species.” To explain this, he makes use of his analogy between animal spirits and rays of light. Unless, he writes, “humid particles of air” are mixed with the light, no images are transmitted of “an Optick scene.” He seems to have a confused notion of the Epicurean visual theory, wherein replicas of objects continuously stream through the atmosphere from object to viewing eye. In the same way, the translucent watery latex is vital in fixing the humid particles of air, which outline the forms of visual images, and then transporting them back to the brain. All this seems, of course, very strained and fantastical even for the pre-Newtonian 17th century.41

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Theory and Argument Finally, how is muscular movement, that great problem of 17th-century neurophysiology, generated? Again Willis, compared to Borelli, is vague and unanalytic. He maintains that every part of the anatomy receives two nutritive (p.139) streams, vascular and nervous—or, as he puts it, “nourishable” and “spirituous.” He then makes use of the theory “delivered lately by the most ingenious Doctor Stensen.”42 We saw, in Chapter 7, that Stensen suggested that the fine structure of muscle consisted of sets of parallelepipeds. Willis argues that, when a muscular contraction is willed, the nerve delivers an extra quantity of animal spirits to what is already present, quiescent, in the muscle. The “arterious Juyce,” he says, mixing with this extra quantity of spirits, causes them to become more active, “whereby the Muscle is suddenly intumified” by the spirits instantaneously expanding “like the explosion of Gun-powder.”43 This expansion causes the parallelepipeds to move, as Stensen suggested, in such a way that the muscle contracts. It is clear from the foregoing that Willis has, as Stensen said, spoiled his accurate neurology with too thick an overlay of speculative neuropsychology. Indeed, Eugenius, the editor of Willis’s London Practice of Physick, in an excerpt of Willis’s medicine published in 1689, 14 years after Willis’s death, is scathing about Willis’s predilection to theory. He writes that “his anatomy of the brain, muscular motion, and the soul of brutes…are all theory and contain nothing of Practice in them.”44 He claims that the practicing physician need not trouble himself with them. Nevertheless, readers of the Practice of Physick will find that even the practical part of that treatise is permeated by theory: the ancient theory of animal spirit.45 As Erasmus Darwin was to point out at the end of the next century, medicine needs theory to hold its complicated phenomenology together and make sense to the practitioner.46 Willis, in addition to being a practical and very successful physician, was very clearly driven by this passion to understand humans and how their functioning and dysfunctioning could be fitted into a wider philosophy. Although this attempt was destined to fall into disrepute as the theory of animal spirits slowly collapsed, his account of brain anatomy and of the positions and distributions of the cranial and spinal nerves have stood the test of time, as have the magnificent illustrations that Wren provided.

Concluding Remarks

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Theory and Argument The “biomedical scientists” (to give them an anachronistic title) considered in the previous two chapters are, of course, only a sample, though perhaps the best-known sample, of the many natural philosophers and physicians working in the 17th century. They were surrounded by a penumbra of lesser-known names, all seeking to understand the brain and nervous system in this new age where the old certainties, the old world-picture, was being undermined by new observations and new experiments. It was truly an age of transition. We have seen how many of the major players in 17th-century biomedical science looked backward as well as forward. It is always a mistake to regard them as “lisping moderns,” for their understanding of the nature of things was very different from ours. The “modern” elements in their thought, the seeming prefiguration of our synaptic biochemistry in their myoneural physiology, for instance, was not seen in their day, as we see it from our perspective. It was seen as part and parcel of a synthesis of half-medieval, half-early-modern thought. It was fleshed out in metaphors derived from the everyday life of the time. Willis’s psychoneural theory was complete and explanatory in itself. We can see in his Casebook and in his London Practice of Physick that his theory, however much derided by more empirical minds, formed a framework that made sense of his observations of sick and deranged persons. His metaphors centered it in the world familiar to 17th-century men and women. It is small wonder that demand for his services was overwhelming and, indeed, overwhelmed him, so that he died at the comparatively early age of 54. This chapter was originally titled “Animal Spirit and Hot Air,” partly because we now regard the theory as so much “hot air” and partly because animal spirit itself seemed to many 17th-century physicians and natural philosophers to be akin to “hot air.” Animal spirit(s), as the chapters in this book have shown, is a concept of great antiquity. In the 17th century they retained for many thinkers their ambiguous psychoneural, half-material, half-“spiritual” character, and this ambiguity was destined to last many years into the future. Yet, as we have seen in this chapter, thinkers like Borelli and, in the previous chapter, Swammerdam were beginning to dissect away their “spiritual” dimension and treat them as material as the rest of the body. But we have also seen that many, if not all, of these 17th-century biomedical thinkers eschewed the thoroughgoing materialism of Descartes. They worked much closer to the living bodies of humans and other animals than did that essentially mathematical philosopher. Centuries were to pass before living organisms could be realistically seen as hugely complex, chemical machines, and during that time the concept of the inorganic evolved as much as that of the organic. But that is another story, and a great one, and must be told elsewhere. Notes:

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Theory and Argument (1) Willis, 1681, p. 136: “We shall proceed to the remaining task of our Anatomy, to wit, the Neurologie or of the nerves in particular.” Willis’ Cerebri anatome dates from 1664 and was “Englished” by Samuel Pordage in 1681. For a facsimile of Pordage’s translation and more on the term neurology, see the Feindel (1965) edition of Willis. (2) Thomas Beddoes appears to have been the first to publicly recognize John Mayow’s prescience in a letter to Dr. Edmund Goodwyn dated February 12, 1790. See Mayow (1674): Introduction. Mayow’s ideas on muscular attraction are discussed in Chapter 11. (3) Glisson, 1672. (4) See Giglioni, 1996. (5) This experiment, although demonstrated in 1669, was not published until 1756 in Birch’s History of the Royal Society, Vol. 2, p. 412. (6) See introduction by Margaret Nayler to Croone’s De ratione motu musculorum (1664). (7) Sturm JC (1676–85). Collegium experimentale sive curiosum. Nuremberg. Quoted by Margaret Nayler, ibid. (8) This and other particulars from Croone’s entry in the Dictionary of National Biography. (9) Croone, 1664. (10) Ibid., p. 89. (11) Ibid., p. 77. (12) Ibid., p.101. Croone is also influenced by Harvey’s circulation theory. He writes that the “spirituous juice is drawn through all the nerves in a constant circuit” (p. 101). (13) Ibid., p. 101. (14) It is not difficult to prove that when the sides are kept constant the rhomb with the greatest area is a square (i.e., a right-angled rhomb). (15) The second edition was read in 1674/5 in the Surgeons’ Theatre and published in the Philosophical Collections of the Royal Society under the title, “An Hypothesis of the Structure of Muscle and the Reason of its Contraction” (Croone, 1681).

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Theory and Argument (16) Van Leeuwenhoek, 1674, 1677. In his 1677 contribution he writes (with some exaggeration!), “If I may judge by my sight, I must needs say that ten hundred thousand of them would not make up one grain of gravel sand.” Later, as we noted in Chapter 7 (Fig. 7.10), he arrived at a much more accurate understanding of the microscopic structure of striated muscle. He no longer “saw” globules but fibers! (17) Croone, 1675, p. 23. (18) Ibid., p. 25. (19) Details of Borelli’s scientific life are to be found in Settle, 1970. The first part of De motu animalium was published in 1680 and the second part in 1681. (20) Quoted in Borelli (Maquet trans.), 1989, p. 6. (21) Boorstein, 1983. (22) This analogy was very common in the first part of the 17th century and was considered, and discarded, by many of the anatomists of the time. Borelli devotes many pages and discusses many experiments that disprove the idea. (23) Borelli does not accept that muscles do not expand on contraction. He makes this quite clear in Vol. 2, Proposition XXVIII: “Muscles actually swell and increase in volume.” (24) A well-illustrated review of Willis’s life and contributions to medicine is provided by Molnár, 2004. Details of his life are also to be found in the Dictionary of National Biography, in Munks Roll (biographies of Fellows of the Royal College of Physicians), in Isler (1968), in Dewhurst (1980a, 1980b), and the biography by Aubrey, 1999. (25) A fictionalized account is to be found in Iain Pears’ novel An Instance of the Fingerpost (Pears, 1998). (26) Willis’s title has been a source of confusion. De anima brutorum or, as Pordage translates it, The Soul of Brutes, is not primarily a tract on animal psychology. Willis uses the age-old tripartite classification of vital, animal, and rational “souls.” Whereas, as Aristotle taught, animals share with humans the first two, only humans possess the third. Thus Willis’s treatise principally concerns the sensitive or animal “soul” in man, which he takes to be corporeal, leaving discourse on the immortal, rational “soul” to higher authority. (27) Quoted in Dewhurst, 1980a, p. 26. (28) Hutchinson, 1799, vol. 2, p. 484. (29) Quoted in Meyer and Hierons, 1965b. Page 29 of 31

Theory and Argument (30) Willis, 1681, Preface. He also thanks his collaborators for helping him in long, theoretical discussions about the significance of the anatomy they were displaying. Willis always had larger designs than the mere dissection of the brain: he wanted to know how it all worked, how it related to wider understandings of human life, and, in particular, how and why it sometimes fell into disease. (31) Willis, 1681, Preface. (32) Willis, 1672/1683, p. 23. (33) Ibid., p. 24. (34) Ibid., p. 25. (35) Willis, 1681, Chapter XV. (36) Ibid. In The Practice of Physick he makes use of this understanding of the cerebellum to explain the origin of the “incubus or nightmare.” He argues that the feeling that breathing is impeded, that it is impossible to move a limb, that a heavy incubus sits on the stomach, is due to an obstruction that prevents spirits leaving the cerebel (Willis, 1689, p. 408). (37) Ibid., Chapter XI. (38) Ibid., Chapter XIX. (39) Willis, 1681, p. 127. (40) Willis, 1672/1683, p. 24. (41) In Chapter XV of De anima brutorum Willis outlines his Epicurean visual theory: “Tis needful that Seeing should be so performed at a distance, that visible things might diffuse, and everywhere propagate themselves by their Images far and wide; so that wherever the eye is stop’d, the images of some Bodies objected are met with…[these images] consist of most thin little bodies.” So far as the rays themselves are concerned, it is clear that he really does not know what to think. Are they, he asks, actually streams of “effluvia’s darted forth from a lucid Body,” or do the images flying off visible bodies affect particles in the atmosphere so that by “inkindling them render them luminous. And these at length others, and so a diffusion on every side of Light or Images is propagated as it were by a certain waving” (p. 75). (42) Willis, 1681; “Of Musculary Motion,” p. 35. (43) Ibid., p. 129. (44) Willis, 1689, Preface. Page 30 of 31

Theory and Argument (45) Willis’s practical medicine (even as edited by Eugenius) makes great use of the concept of animal spirits. In melancholy, for instance, Willis writes that “animal Spirits…whereas they ought to be transparent, subtle and light… become obscure, opake and darkish, so that they represent the images of things covered as it were with a Shadow or obscurity” (p. 461), and he employs the concept of animal spirits to provide similar psychophysical explanations of vertigo, madness, headache, apoplexy, etc. (46) Darwin, 1796, Preface: “There are some modern practitioners, who declaim against medical theory in general, not considering that to think is to theorize…a theory founded upon nature…should bind together the scattered facts of medical knowledge…and capacitate men of moderate abilities to practice the art of healing with real advantage to the public.”

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Introduction

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.143) Introduction It has often been remarked that the splitting of the historical process into centuries is entirely arbitrary. It is merely a matter of human convenience and bears no necessary relation to the flow of events and ideas. This is especially the case with the history of science, where the notion of progress is more evidently valid than in other areas of history. Thus, in the next section of our book, we take up the story of animal spirits at the end of the 17th and follow it on into the 18th century. There, however, is no sharp line of demarcation dividing December 31, 1699, from January 1, 1700; many of the scientists we discuss in the coming section straddle the demarcation. This is, for instance, true of perhaps the greatest of them all: Sir Isaac Newton. He was born on January 4, 1643, and died on March 31, 1727. His major work, Principia mathematica, was published 1687, with a second edition in 1713 and a third in 1726. His second major work, Opticks, appeared in 1704, with a second edition in 1717/18, a third in 1721, and a fourth in 1730. Although Principia mathematica finally showed that the heavens and the Earth obeyed the same mathematical physics, it was the Opticks, and especially the increasing number of Queries that Newton appended to the second, third, and fourth editions, that finally established the experimental method in science.1 We shall notice the fruitfulness of one of these Queries when we come to consider vibration theories of nerve conduction and cerebral physiology in Chapter 9. They usually took the form of speculative hypotheses.2 Newton asks, for instance, in Query 29, “Are not the Rays of Light very small Bodies emitted from shining substances?” and goes on to consider the pros and cons of this idea, suggesting experiments that might be designed to prove or disprove it.

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Introduction It was this second Newtonian tradition, the tradition of experimental science, that dominated 18th-century work in neurophysiology. Although, as we noted in the last section, especially in Chapter 7, experimental work had been gathering momentum throughout the 17th century, it was only in the 18th century that it dominated scientific thought, and it was consequently in this century that the doctrine of animal spirit fought its last, despairing, rear-guard action. This was not, of course, the only rear-guard action fought during the 18th century, for this century has often been seen as “the Age of Enlightenment,” a self-confident period in which the old dispensations and the old understandings were gradually overcome. It witnessed the opening of the world to European exploration and military/commercial power. It was the age of Louis Antoine de Bougainville, James Cook, and, at the very end, of Alexander von Humboldt. It was the age of collections, of systematization, of Carl von Linnaeus’ Systema naturae, of James Hutton’s Theory of the Earth, and Erasmus Darwin’s Zoonomia. But it was also the age of secularization. The passionate religious conflicts of the previous century had left an uneasy settlement. Edward Gibbon published his great sardonic history of the decline and fall of the Roman Empire. Voltaire wrote passionate diatribes against the dogmatic stance of the Catholic Church. Goethe’s polymathic work included, as he writes in one of his final letters, “no confession of faith to which I could ally myself without reservation.”3 But if the passionate religious disputes of the previous century had died back, this was not the case with politics. Revolutionary warfare, displacing the old order, broke out in North America in the 1770s and in France in the 1780s. Many lives were lost before North America gained its independence and France emerged from the revolutionary terror and the Napoleonic wars. And, of course, these were not the only revolutions. Equally important in our history of the decline and fall of animal spirits was the revolution in the means of production, distribution, and trade. This great upheaval began first in the British Isles with the development of steam power and all its associated machinery. When Samuel Johnson’s biographer, James Boswell, visited the English Midlands in 1776 he was shown around one of the marvels of the age: Matthew Boulton’s Manufactory just outside the then rapidly growing settlement of Birmingham. In response to Boswell’s query Boulton replied; “I sell here, Sir, what all the world desires—POWER.” Engineers were in process of turning the world upside down.

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Introduction It was against this background that anatomists and physiologists sought to understand the workings of the brain and nervous system. Throughout the 18th century the argument continued. The animal spirit doctrine was still deeply embedded in the medical-biological thought of the era—and not only in the thought of professional physicians and their tutors in the great medical schools, but also among the general population. For Tristram Shandy in Laurence Stern’s novel of the 1760s it was simply conventional wisdom: “You have all, (p.144) I dare say, heard of the animal spirit. Nine parts in ten of man’s sense and nonsense…depend on its motions and activity.”4 It was, as we shall see, only towards the end of the century that an acceptable “successor theory” of nerve function became available. That theory was developed by many workers and explorers. The story of electric fish and the frog work of Galvani and Volta will be told in Section 5 of this book. But until an understanding of that mysterious “subtle fluid,” electricity, was achieved, animal spirits remained the default explanation of the working of the brain and nervous system. It is to these explanations that we turn in the next chapters. We shall start with an account of a totally different concept. At the end of the second edition of his greatest work, Principia mathematica, Newton gave new life to the ancient notion of an exceedingly rarefied medium—“world pneuma” for the Stoics, “aether” for Newton—that allegedly pervaded the universe and everything in it. This included, of course, all living beings, so he went on, both in the Principia and in his Opticks, to suggest a neurophysiology based on vibrations in the aether confined in the “capillamenta” of the nerves. This idea was taken up by David Hartley, later in the 18th century, and developed into a comprehensive physiological psychology. Newton’s and Hartley’s work is reviewed in Chapter 9. The theory, partly due to misunderstandings, never found favor with mainstream anatomists and physiologists, although Hartley’s associationist psychology was immensely influential. The next chapter returns to a discussion of the development and elaboration of the animal spirit doctrine by the great biomedical thinkers of the 18th century. The animistic ideas of Georg Ernst Stahl are reviewed and it is shown how they were found wanting, leading to a move back towards a more mechanistic physiology. One great figure stands out—Herman Boerhaave, sometimes referred to as the teacher of Europe. The major part of the chapter is devoted to his profound and comprehensive synthesis of early-18th-century work on the anatomy and physiology of the neuromuscular system. The chapter ends with a review of other important figures in 18th-century biomedicine and a look forward to the electrical theories of the next century.

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Introduction The last two chapters in this section deal with a quite different set of ideas about how organisms respond directly to stimuli without the involvement of animal spirit, thus opening the way to the materialistic theorizing that developed in the 19th century. It is a long story, also originating in antiquity, which came into play as a serious competitor of the animal spirit theory only at the end of the 17th century. Chapter 11 follows the trail of views about such physical or natural responses (as opposed to psychical or animal ones), from the ancient Greek philosophers up to the revolutionary medical theories posed by Francis Glisson and Giorgio Baglivi, who claimed that fibers composing the organs—particularly muscle—are themselves directly responsive to irritation. Chapter 12 then examines the rapid development of the notion of irritability in the 18th century, both through the formulation of an elaborated theory of fibers, and by the envisioning of different sensitive-motive “principles” resident in the body itself, rather than necessarily ruled by the psychic factors in the brain. Most of this multiple search in various directions was carried out by former students of the above-mentioned Herman Boerhaave, and culminated in the monumental work of the most influential of them all—Albrecht von Haller. Physiology of the neuromuscular system could not continue to be the same after Haller, neither conceptually nor methodologically, thus setting the stage for the conquests described in last section of our book.

(p.145) Chronology Science

Cultural Context

1687 Newton: Principia (1st edition) 1702 Baglivi: Specimen quatuor librorum de fibra motrice et morbosa 1704 Newton: Opticks (1st edition)

1704 Swift: Tale of a Tub

1708 Stahl: Theoria medica vera

1707 Act of Union between England and Scotland

1708 Boerhaave: Institutiones medicae 1710 Petit: Lettres d’un médecin 1713 Newton: Principia (2nd edition) 1714 Boerhaave begins clinical teaching 1717 Newton: Opticks (2nd edition) 1726 Newton: Principia (3rd edition) 1727 Petit discovers function of cervical sympathetic nervous system

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Introduction

Science 1730 Newton: Opticks (4th edition) 1731/5 Gray: electrical experiments 1731/51 Gorter: Medicinae compendium 1732 Boerhaave: Elementa chemiae 1737 Kinneir: A New Essay on the Nerves 1737/8 Swammerdam (published by Boerhaave): Bybel der nature (Biblia naturae) 1742/6 Boerhaave: Institutes 1744 Swieten: Commentaries 1745 Whytt: An Enquiry.… 1745/6 Invention of Leyden jar 1745 Kratzenstein’s medical applications of electricity 1746 Nollet: Essai sur l’electricité des corps 1746 Monro (primus): The Anatomy of Human Bones and Nerves 1746 Hartley: Conjectures 1747 Haller: Primae lineae physiologiae 1747 La Mettrie: L’homme machine 1749 Hartley: Observations on Man 1751 Whytt: An Essay on the Vital and other Involuntary Motions of Animals 1751 Franklin: Experiments and Observations on Electricity 1753 Beccaria: Dell’elettricismo “artificiale” et “naturale” 1755 Haller: Dissertation on the Sensible and Irritable Parts of Animals 1755 Whytt: Observations on Sensibility and Irritation 1755 Whytt: Physiological Essays

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Cultural Context

Introduction

Science

Cultural Context

1757/66 Haller: Elementa physiologiae corporis humani 1757 Adanson: Histoire naturelle de Senegal 1759 Voltaire: Candide 1758 Linnaeus: Systema naturae (10th edition) 1760 Wesley: Desideratum, or Electricity Made Easy (10th edition) 1765 Whytt: Observations…. on Nervous, Hypochondriac, or Hysteric Disorders 1766 Mesmer: De planetarum influxu 1767 Priestley: History and Present State of Electricity 1768 Cook’s first voyage 1769 Bancroft: Natural History of Guiana 1770 Cullen: Lectures on the Institutions of Medicine 1772 Walsh: Experiments on the Torpedo… 1772 Priestley: The History and Present State of Discoveries relating to Vision, Light and Colours 1773 Walsh: On the Electric Property of the Torpedo 1773 Hunter: Anatomical Experiments on the Torpedo 1775 Mesmer demonstrates “animal electricity” 1775 Hunter: An Account of Gymnotus

1776 Declaration of

electricus

Independence in America

1778 Mesmer develops group therapy using “animal magnetism” 1779 Prochaska: De structura nervosa

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Introduction

Science

Cultural Context

1780 d’Eslon: Observations sur le magnetisme animal 1784 Prochaska: Functions of the Nervous System 1787 Fontana: Venom of the Viper

Notes:

(p.146) (1) It is also noteworthy that whereas the first edition of the Principia was published in austere Latin the Opticks was written in flowing English. This also helped to distinguish two classes of readers: those highly educated in classics and skilled in mathematics and those uncomfortable with the ancient tongues but, like Stephen Hales, Joseph Black, and Benjamin Franklin, eager to try experiments. (2) Famously Newton disdained speculation: “hypotheses non fingo.” But this dismissal is more honored in the breach than in the observance. The hypotheses in the Opticks, however, are always followed by several pages setting them in the context of wider understanding of the nature of things and suggesting practical means of showing them correct or incorrect. (3) Letter to Sulpiz Boisserée (March 22, 1831). Quoted in Boerner, 1981, p. 82. (4) Sterne, 1760, p. 1.

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Vibrations and Subtle Fluids

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Vibrations and Subtle Fluids C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0009

Abstract and Keywords This chapter introduces the vibration theory, which was unable to dethrone the doctrine of animal spirit. It discusses Isaac Newton's “aether,” which supposedly encompassed the universe and everything in it, including all living beings. Newton suggested a neurophysiology that was based on vibrations in the aether, which were confined in the nerves' “capillamenta.” It then studies David Hartley, who adapted Newton's idea and turned it into a comprehensive and physiological psychology. This chapter stresses that the vibration theory was able to reflect a growing disillusionment with the received doctrine, but didn't find favor with mainstream physiologists and anatomists. Keywords:   vibration theory, aether, Isaac Newton, capillamenta, David Hartley, physiological psychology

And first I suppose that there is diffused through all places an aethereal substance capable of contraction and dilatation, strongly elastic, and in a word, much like air in all respects, but far more subtil. Isaac Newton: Letter to Robert Boyle, February 18, 1678/91 These vibrations…must be conceived to be exceedingly short and small, so as not to have the least efficacy to disturb or move the whole bodies of the nerve or brain.

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Vibrations and Subtle Fluids David Hartley, 1749, Observations on Man, p. 8 In the last two chapters of the preceding section (Chapters 7 and 8) we saw how the traditional neurophysiology of animal spirit coursing down hollow nerves to carry messages between the brain and the periphery was being sharply questioned by new experiments and observations. Although, as we shall see in this chapter, it retained its popularity into the 18th century, this was largely because a coherent alternative theory had yet to be found. This, however, was not for want of trying, and perhaps the most interesting attempt to find an alternative was proposed by the greatest scientist of the age, Sir Isaac Newton. Newton’s proposal appeared first in the Scholium generale, which he appended to the second edition of his greatest work, Principia mathematica, in 1713, and was expounded again in the Queries that he placed at the end of later editions of the Opticks. Newton’s great fame brought attention to this theory, a theory that replaced animal spirit and hollow nerves with vibrations in the infinitesimal particles of a subtle fluid, the aether, which he conceived to permeate solid nerve fibers. This idea was taken up by another significant 18th-century thinker, David Hartley, in his Observations on Man, and was developed to provide a neurophysiological basis for his far-better-known association psychology. It is to these two great figures that this chapter is devoted.

Sir Isaac Newton The 18th century was dominated by Sir Isaac Newton (Fig. 9.1). Alexander Pope’s well-known lines describe how his huge achievement seemed to the 18th century: “Nature and Nature’s Laws lay hid in Night God said ‘Let Newton be’ and all was light.” In 1931, Einstein, in his introduction to the tercentenary edition of the fourth edition of the Opticks, pays homage to Newton’s genius but also observes that he was fortunate to live at the time when he did. The world was ready for him.2 He completed what Dijksterhuis called “the mechanization of the world picture”3 and revealed a world, as Burtt remarks, “hard, cold, colorless, silent and dead; a world of quantity, of mathematically computable motions in mechanical regularity”: a vision that “finally overthrew Aristotelianism and became the predominant world-view of modern times.”4 Newton’s greatest work, Principia mathematica, appearing first in 1687 and republished in second and third editions in 1713 and 1726, unified heavenly and terrestrial dynamics (Fig. 9.2). It showed that the same mathematical laws governed the movements of stars, planets, projectiles, falling apples, and the ocean’s tides. It was a truly remarkable unification and fully deserved Pope’s encomium. It carried (p.148)

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Vibrations and Subtle Fluids all before it and penetrated not only the academic world of physics and mathematics but also the realm of popular thought. Voltaire published a popularization in 17385 and Francesco Algarotti published the engagingly titled Sir Isaac Newton’s Philosophy Explain’d for the Use of Ladies in Italy a year earlier in 1737.6 This, like Voltaire’s popularization, was quickly translated into a number of other European languages.7 In addition to published works, Newton’s thought was popularized by Anglican clergymen. They used a series of sermons, endowed through the will of Robert Boyle, to spread Newton’s vision of a universe governed by deeply

Figure 9.1: Isaac Newton by Godrey Kneller in 1689, at the age of 46 (‹en.wikipedia.org/wiki/Isaac_Newton›).

thought-out laws.8 In addition, an increasing number of itinerant lecturers roamed the land, demonstrating experimental Newtonianism in coffee houses and provincial societies.9

Figure 9.2: Title page of first edition (1687) of the Principia.

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Vibrations and Subtle Fluids The fact that many Anglican clergymen felt that Newton was far from teaching a soulless atheism suggests that Burtt’s assessment of Newton’s message does not tell the whole story. The notion that the world was governed by laws, that it was to be compared to a mechanism, a clockwork, suggested to many that there must be a designer. In 1714 William Derham published the first of a number of tracts using the argument from design to prove that a just and benevolent creator must exist,10 and at the very beginning of the next century William Paley publicized the famous watchmaker argument for an intelligent creator—an argument that exercised the mind of the young Charles Darwin.11

The Aether But in the depths of Newton’s mathematical natural philosophy there lurked a problem. In his greatest work, Principia mathematica, where he had shown that the tides, the fall of an apple, and the movements of the planets all obeyed the same mathematical law, he had, of necessity, to make use of what to many seemed an occult principle: action at a distance.12 How could a body act where it was not? In the great Scholium generale, which he appended to the second and subsequent editions, he admits that he has no idea how such a phenomenon could occur, and it is here that he inserts the famous phrase hypotheses non fingo—I frame no hypotheses—and, in a letter to Bentley, he writes that “the cause of Gravity is what I do not pretend to know.”13 Action at a distance, through the vacuum of empty space, was a great and abiding puzzle. Newton himself remarks that no one of any philosophical sophistication could accept such an idea. For Newton was also a convinced atomist. He makes this abundantly clear in Query 31 of the Opticks: “it seems probable to me that God in the beginning form’d (p.149) Matter in solid, massy, hard, impenetrable Particles…even so very hard, as never to wear or break into pieces.” He goes on to explain, just as the ancient atomists explained, how the macroscopic bodies, with which we are familiar, are formed of these particles and that changes of these “corporeal things” are brought about by separations and rearrangements of their atomic constituents.14 For atomists, cause and effect is a matter of contact. The infinite happenings of the world are, at root, due to tactile interactions of billiard-ball–like atoms far below the level of visibility.

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Vibrations and Subtle Fluids Action at a distance breaks this paradigm. How could a massy object, such as the moon, cause movement in another massy object, such as the ocean, at an astronomical distance? Yet, according to the Principia, it did! To save the appearances, Newton had perforce to invent an unseen imponderable medium, the aether. It was this unseen medium that transmitted gravitational force and the rays of light. Thus, although one of Newton’s best-known positions was that he feigned no hypotheses, he did, in this case, feign the greatest hypothesis of them all—an hypothesis that persisted down through the centuries until Michelson and Morley cast severe doubt on it at the end of the 19th century15 and Einstein did away with it altogether at the beginning of the 20th. Newton needed this imponderable medium for yet another purpose. At the beginning of the 18th century, the science of statistical thermodynamics, with its molecular and atomic accounts of the conservation of energy, lay far in the future. Newton’s theory in consequence encountered another glaring problem: if the collisions between the massy particles of the world were not entirely elastic,16 as common experience showed them not to be, the quantity of motion in the universe would quickly diminish and ultimately disappear altogether. Newton’s first law of motion, that particles continue at rest or uniform motion in a straight line unless acted upon by a force, implied, after all, a fundamental “laziness” in matter, that he defined as “vis inertiae.” But the world around showed no sign of running down, or collapsing like a deflated balloon. There must, accordingly, be some continuing source of new motion and this, to cut a long story short, Newton believed to be provided by the continuous exhalation of aether from the interstices of the Earth.17 What form did the aether take in Newton’s mind? Was it material or immaterial? There seems little doubt that it was material. In an early letter to Oldenburg, Secretary to the Royal Society, he writes of “an aethereal medium, much of the same constitution with air, but far rarer, subtler and more strongly elastic.”18 At this time, in 1675, he also considered aether to consist of a mixture very much as air is a mixture of various vapors and exhalations. Later his concept changed somewhat and aether became a single unmixed substance. In any case the aether, in Newton’s thought, was very definitely a material substance.

Newton’s Vibrationism Now what has all this to do with animal spirit? It turns out quite a lot. In a famous passage at the very end of the Principia Newton writes of a “most subtle spirit” that

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Vibrations and Subtle Fluids pervades and lies hid in all gross bodies; by the force and action of which spirit the particles of bodies mutually attract one another at near distances and cohere if contiguous; and electric bodies operate…; and light is emitted, reflected, refracted, inflected and heats bodies; and all sensation is excited, and the members of animal bodies move at the command of the will, namely by the vibrations of this spirit, mutually propagated along the solid filaments of the nerves, from the outward organs of sense to the brain, and from the brain to the muscles [our italics].19 Newton concludes this fascinating final passage of the Principia by admitting that there is not yet “that sufficiency of experiments which is required to an accurate determination of the laws by which this electric and elastic spirit operates.” But his interest in it never waned. When we turn to his second great work, the Opticks, we find it plays a major role in his neurophysiological ideas. We can see, however, that it is a very different concept from that of the animal spirit we met in the earlier parts of this book. It is very much part of a physicist’s view of the world. It is, in particular, very much a part of his own great synthesis, and has no connection at all with the animal spirit of Erasistratus, Galen, and Descartes. On the other hand, there is, of course, seldom anything new under the sun. Vibratory neurophysiologies had often been suggested before Newton’s time. Galileo, for instance, proposed in his 1623 publication, Il Saggiatore, that “sounds are produced in us and heard when…a rapid vibration of the air in the form of extremely minute waves moves some cartilage in the tympanum that is in our ear.”20 Both Jan Swammerdam and Giovanni Borelli had proposed percussive theories of nerve transmission (Chapters 7 and 8), and William Croone wrote that sensory nerves are able to vibrate “like a bell” and this vibration is transmitted from periphery to the brain. These speculations were, however, taken to an entirely new level by Isaac Newton and his disciple David Hartley. It is not too great an exaggeration to see Newton’s neurophysiology as the first coherent successor theory to the ancient hydrodynamic model. Its outlines can be found in (p.150)

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Vibrations and Subtle Fluids the Opticks (Fig. 9.3). In this great treatise we find that Newton was concerned not only with physical but also with physiological optics. He was concerned to understand not only the way light was reflected and refracted, not only with an analysis of color, but also with the way light affected the eye and with visual perception. Newton was, of course, not the first to concern himself with the way in which the eye worked. The tradition of physiological optics stretches back at least as far as Ibn al-Haytham’s great work in the 12th century (Chapter 4) and perhaps should be traced even further back to the Alexandrians who coined the Greek term for retina—amphiblestroides—and even before that to Alcamaeon in the sixth century BCE. But in the late 16th and early 17th centuries experiments performed on ox eyes had shown very clearly that an inverted image of the visual object was thrown onto the retina at the back of the eyeball.21 We noted in Chapter 6 that Descartes was quite familiar with this idea.

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Figure 9.3: Title page of fourth edition (1730) of the Opticks.

Vibrations and Subtle Fluids Thus, when we read, at the beginning of Newton’s Opticks, an account of visual optics we recognize that he is retelling a well-known account: “when a Man views any Object,” he writes, “the Light which comes from the several points of the object is so refracted by the transparent skins and humors of the Eye…as to converge and meet again in so many Points in the bottom of the Eye, and there to paint the Picture of the Object upon that skin (called the Tunica Retina) with which the bottom of the Eye is covered.”22 We saw in Chapter 6 that Descartes told a very similar story. But Newton’s account of what happens next is very different from Descartes’ (to our eyes) fanciful theory. For, according to Newton, instead of the rays of light affecting filaments in the optic nerve so that valves are opened in the ventricular wall, as Descartes imagined (see Chapter 6, Fig. 6.9), they excite vibrations in the aether imprisoned in the retina and the fibers of the optic nerve. “Is not Vision,” he writes in the 1731 edition of the Opticks, “performed chiefly by the Vibrations of this Medium [i.e., the aether], excited in the bottom of the Eye by the Rays of Light, and propagated through the solid, pellucid and uniform Capillamenta of the optic Nerves into the place of Sensation?”23 It is clear that Newton no longer regarded the nerves as hollow tubes along which animal spirit flowed. Propagation was not brought about, as Descartes and the ancient and medieval natural philosophers had dreamt, by flows of animal spirits along tubular nerve fibers, but by vibrations in the “solid, pellucid and uniform Capillamenta” of the nerves. Indeed, in the same set of Queries appended to the Opticks, he makes his idea quite clear by drawing an explicit comparison between sight and hearing. He asks in his usual rhetorical fashion whether hearing, also, is not brought about “by the Tremors of the Air,” causing vibrations of aether trapped in auditory nerve fibers, which are then “propagated through the solid, pellucid and uniform Capillamenta of those Nerves into the place of Sensation.”24 Finally, having proposed that similar vibratory mechanisms account for the transmission of information to the “sensorium” from all the other senses, he turns his attention to the motor nerves and the motor outflow. He suggests that a precisely similar mechanism obtains. In Query 24 he asks, “Is not Animal Motion perform’d by the Vibrations of this Medium [i.e, aether], excited in the Brain by the power of the Will, and propagated from thence through the solid, pellucid and uniform Capillamenta of the Nerves into the Muscles, for contracting and dilating them?”

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Vibrations and Subtle Fluids Newton is clear that for his theory to work the “Capillamenta of the Nerves” must, as he says, be “solid, uniform and continuous.” Only if this is the case can the aetherial vibrations be propagated “from one end to the other, uniformly and without interruption.” Furthermore, he is clear (p.151) that a nerve observed in dissection is “composed of many Capillamenta.” Newton’s neurophysiology has clearly taken on board the researches of the previous century: researches that, as noted in Chapters 7 and 8, had shown the tubular nerve theory of Descartes and the ancients to be untenable. It is also clear that Newton’s neurophysiology is a fragment of his larger theory of the world. In both the macro- and the microcosmos, the aether and its vibrations play a central role. This is not the place to delve further into Newton’s theory or to discuss the nature of the sensorium to which these aethereal vibrations deliver their messages and from which the will commands the muscles. Sufficient has been said to show that, as in earlier syntheses, the microcosm, man, exhibited in small the characters exhibited by the macrocosm, the world, in large. Enough has been said, also, to show why Newton’s huge reputation throughout the 18th century ensured that his vibratory neurophysiology was not immediately dismissed as a fantasy. Stephen Hales, for instance, pays homage to Newton in his great 1731 work on the cardiovascular system Haemastatics, suggesting that “a vibrating electrical virtue can be conveyed…on the surface of animal Fibers and therefore on the Nerves” [our italics].25 Browne Langrish, a country physician, in his Croonian Lecture on muscular motion given to the Royal Society in 1747, had also been swayed by Newton’s ideas. He went so far as to insist that “the existence of an aetherial medium in the nerves is past all manner of doubt” and, moreover, that the nervous fluid, “in its subtility and velocity” is comparable to “electrical effluvia.”26 Nevertheless, although Langrish had been impressed by Newton’s vibratory theory when he published his initial essay on muscular movement in 1733, and although he states that its existence is “past all manner of doubt” in his 1747 Croonian lecture, he makes no attempt to develop the theory. However, another country physician certainly did. That country physician was David Hartley (Fig. 9.4), and he made it the basis of one of the most influential 18thcentury physiological psychologies.

David Hartley’s Vibratory Neurophysiology Hartley was born in Yorkshire near the town of Halifax in 1705, the son of an Anglican clergyman. He had a somewhat tragic childhood, his mother dying 3 months after his birth and his father when he was 15. He nevertheless received an excellent education, first at Bradford Grammar School and then at Jesus College, Cambridge, where he read mathematics, theology, and classics. It was intended that he follow his father into the Anglican Church but he never did, finding it impossible, he said, to assent to the Church’s 39 articles. Instead, despite never taking a medical degree,27 he took up a medical career and practiced first at Newark, and then Page 9 of 25

Vibrations and Subtle Fluids successively in Bury St. Edmunds, London, and, finally, Bath, where he died at the end of August 1757. He married twice, first to Alice Rowley in 1730, who lived but a year, dying giving birth to a son, David, in 1731, and second to Elizabeth Packer in 1735. She gave birth to two children and outlived her husband by 21 years, eventually dying in 1778. Her health was, however, always precarious and this was largely the reason why Hartley moved his practice from London to Bath in 1742. Hartley himself was never healthy, suffering grievously from bladder stones, for which he actively sought a cure and which was, in fact, the subject of his first publication.28

Hartley’s fame rests upon Observations on Man, his Frame, his Duty, his Expectations, which he published in 1749 and was republished in several editions

Figure 9.4: David Hartley (‹www.hartleyfamily.org.uk/images/ davidhartley1705.jpg›).

and numerous translations throughout the late 18th and early 19th centuries.29 He had, in fact tested out his ideas 3 years earlier in a little-noticed treatise, Conjecturae quaedam de sensu, motu et idearum generatione (Various Conjectures on the Perception, (p.152)

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Vibrations and Subtle Fluids Motion and Generation of Ideas).30 This was published as an addendum to the treatise on bladder stone from which, as we noted above, Hartley, like so many of his contemporaries, including Sir Isaac Newton, suffered acutely. The Conjectures encapsulated the major themes of the neuropsychology that Hartley was to develop at greater length in the first part of the Observations (Fig. 9.5).

The Observations, Hartley writes in his preface, is in fact the fruit of thoughts, and separate papers, stretching back some 18 years. It consists of two parts: an associationist neuropsychology and an ethical/ theological treatise, outlining man’s duties and his consequent expectation of heaven or hell. It is clear that it is the composition of a deeply religious mind and is ultimately intended to support the Figure 9.5: Title page of first edition Christian religion as given in (1749) of Observations on Man. the Scriptures. Hartley’s God is the God of the mystics, of Abraham and Jacob, and not that of philosophers and scientists such as Descartes and Spinoza. This is made abundantly clear in the second part of his treatise. In a final eschatological sentence he writes: The present circumstances of the world are extraordinary and critical, beyond what has ever yet happened. If we refuse to let Christ reign over us, as our Redeemer and Savior, we must be slain before his face, as enemies, at his second coming.31

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Vibrations and Subtle Fluids Fortunately, we need not follow Hartley’s theological arguments in this chapter. We are concerned only with the first part of his work, which outlines his vibrationist neurophysiology and his associationist psychology. The latter was extremely influential. The young Coleridge was sufficiently impressed to name his first child after the philosopher.32 Erasmus Darwin, Joseph Priestley, John Stuart Mill, and William Carpenter and, on the other side of the Atlantic, Benjamin Rush were all affected. The vibrationist neurophysiology was, on the other hand, not so influential. Indeed, when Joseph Priestley edited a new edition of the Observations in 1775, he omitted the vibration theory in its entirety as too difficult for the average reader.33 It is this vibrationist neurophysiology, however, that forms an alternative to the theory of animal spirit, which, as we saw in the previous section of this book, was wilting in the face of fresh observations and new experiments. Acute minds, moreover, recognized that the vibrationist neurophysiology formed a vital underpinning for Hartley’s influential associationist psychology. Indeed, the two parts of his book formed a unity, with the one supporting and completing the other. Coleridge saw this and wrote in his Biographia Literaria of 1817 that It is fashionable to smile at Hartley’s vibrations and vibratiuncles; and his work has been re-edited by Priestley with the omission of the material hypothesis. But Hartley was too great a man, too coherent a thinker, for this to have been done consistently or to any wise purpose. For all the parts of his system, as far as they are peculiar to that system, once removed from their mechanical basis not only lose their main support but the very motive which led to their adoption.34 Whatever the rights and wrongs of Coleridge’s position, let us now turn to the vibrationist neurophysiology with which Hartley’s great work starts. It has been lauded as the earliest example of a fully worked-out neurophysiology.35 Hartley is quite open about where he obtained the inspiration for his theory. “The doctrine of vibrations,” he writes, “is taken from some hints concerning the performance of sensation and motion which Sir Isaac Newton has given at the end of his Principia, and in the questions annexed to his Opticks,” while the association of ideas is from “What Mr. Locke, and (p.153) other ingenious persons since his time, have delivered concerning the influence of association over our opinions and sensations.”36

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Vibrations and Subtle Fluids We looked at these Newtonian “hints” in the preceding section of this chapter. We saw that they suggested that the nervous system was pervaded by a subtle elastic medium, the aether, consisting of “Particles…exceedingly smaller than those of Air, or even than those of Light.”37 This was the hypothesis that Hartley picked up and developed in the Conjectures and Observations. He starts by defining the parts of the nervous system. The brain, he writes, is that which lies within the skull. Sensibility and the power of motion, he continues, are conveyed to all parts from the brain and “spinal marrow…along the nerves.” These, he asserts, “arise from the medullary, not from the cortical part [of the brain], and are themselves of a white medullary substance.”38 In other words, he is clear from the outset that, in contrast to our present understanding, it is the white matter of the brain and not the cortex that is its most important part. And this, he maintains, is no mere speculation but is shown by the anatomical and experimental evidence accumulated in the previous century. Thus, in Proposition 1 of Various Conjectures, he writes: When any considerable injury is done to the medullary substance [i.e., white matter] of the brain, sensation, voluntary motion, memory and intellect are either entirely lost or much impaired.…But this does not hold equally in response to the cortical substance of the brain; perhaps not at all, unless as far as injuries done to it extend themselves into the medullary substance. From these and similar observations Hartley concludes that the white medullary substance is the seat of the sentient soul.39 In the second proposition of the Conjectures, he adds, “the medullary substance of the brain is also the immediate instrument of ideas.”40 He believes he has a good reason for situating these important mental faculties in the white matter. He argues that, in contrast to the gray matter of the cortex, the white matter is homogeneous and uniform. He has no idea that it consists, as we recognize today, of masses and tracts of nerve fibers. Instead he conceives it to consist “of a texture of vessels so small and regular, as that it may have no vacuity or interval in it.”41 The seeming homogeneity and uniformity of the white matter is important for Hartley, as it is here, he argues, that the vibrations and miniature vibrations (vibratiuncles) of his neurophysiology occur. In Proposition 5 of the Conjectures he writes that the vibrations are “confined to the limits of the medullary substance, or at least are not diffused into neighboring parts except in somewhat lessened strength, because these parts are harder and heterogeneous and foster a heterogeneous aether in their irregular pores.”42 We can perhaps see, once more, the influence of Newton in this conviction. In Query 12 of the Opticks Newton writes that motion can only be long-continued in bodies that are “homogeneal, so that the Motion may not be reflected, refracted, interrupted or disordered by any unevenness of the Body.”43

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Vibrations and Subtle Fluids Hartley follows Newton further in suggesting that environmental energies impinging on the sense organs set up vibrations or oscillations in the aethereal particles confined in the sensory nerves and that this vibration is transferred along these nerves to the “sensorium.”44 In successive paragraphs of the Observations he shows, just as his great predecessor did, that this mechanism is plausible for sight, hearing, smell, taste, and touch. “These vibrations,” he writes, “are motions backwards and forwards of the small particles…they must be conceived to be exceedingly short and small, so as not to have the least efficacy to disturb or move the whole bodies of the nerve or brain.”45 Hartley is thus very clear that the nerves themselves do not vibrate. This was a misinterpretation that, as we shall see below, often caused Hartley’s theory to be treated with derision by anatomists. Such a notion, writes Hartley, “is highly absurd; nor was it ever asserted by Sir Isaac Newton, or any of those who have embraced his notion of the performance of sensation and motion.”46 Indeed, Hartley is at pains to assert that the vibrating particles are exceedingly small— indeed, as he writes, “infinitesimal” [his italics]. Hartley follows Newton in taking the nerves to be solid “capillamenta.” He is aware that Boerhaave, the greatest anatomist of the age, still regarded them as consisting of small tubuli and the brain to be a gland. He has several complimentary things to say about the Dutchman and is sufficiently impressed by his teachings to suggest that his theory of glandular secretion of “nervous fluid/animal spirits” is not inconsistent with the doctrine of vibrations. But he concludes that his Newtonian neurophysiology is just as persuasive and just as consistent with the evidence as Boerhaave’s glandular theory. Indeed, this seems to be yet another case where a comprehensive theory—in this case vibrationism —seems so convincing, so all-explanatory, that it determines what is observed. It is interesting, moreover, in the context of this book, to note how the doctrine of animal spirit, even in the mid-18th century, was still, in one form or another, the orthodox view and still stood in need of decisive refutation.

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Vibrations and Subtle Fluids Hartley’s vibrationism is not, of course, confined to the sensory nerves. It is also pressed into service to explain the activity of the “motory nerves” and muscular movement. “Vibrations,” he writes, “descend along the motory nerves…in some such manner as sound runs along the surfaces of rivers, or an electrical virtue along hempen strings.”47 When the vibrations arrive at the muscle, they communicate their oscillations to “small particles” within the muscle fibers. This, he goes on, referring to Newton’s Opticks once again, “puts into action an attractive virtue, perhaps of the electrical kind, which lies concealed in the particles of the fibers.” Hartley, however, understands quite (p.154) well that, although the muscle shortens, it does not appreciably alter in volume. The increase in attraction between the aetherial particles in the muscle fibers must thus be quite small. What causes the contraction is a consequence of the microstructure of the muscle. He supposes that the “ultimate fibers” of muscles “bend alternately to the right and left as an eel does, at exceeding short intervals.”48 Thus he says, and he is clearly struggling here, if these zigzags are made more acute by increased attraction of each “zig” for each “zag,” the muscle will become shorter and fatter—as observed. He attempts, rather unconvincingly, to buttress this theory by reference to the “small wrinkles” observed in muscle fibers by van Leeuwenhoek, the “curls” exhibited by muscle after boiling, and the “rhomboidal pinnulae” observed by Stephen Hales in “the abdominal muscles of a living frog.”49 Hartley continues his speculative account of muscular contraction by citing a number of instances that seem to him to support the vibrationist theory. These include the rhythmic contractions of the heart. He suggests that, in contrast to the traditional animal spirit theory, the vibration theory provides a ready explanation. The vibrating particles, he writes, become obstructed once the muscle contracts and the “zigs” approximate the “zags,” and their vibrations consequently diminish so that the muscle relaxes. Further vibrations descending the motor nerves initiate new vibrations and thus contraction, and so on.50

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Vibrations and Subtle Fluids But can this apply to a heart excised from the body, devoid of all motor nerves? The continuation of the heartbeat of “frogs, vipers and some other animals for some time after these have been entirely separated from their bodies,” he writes, “seem utterly inexplicable upon any common suppositions.”51 We see here how Hartley’s Newtonianism begins to run into seemingly insoluble problems. Hartley, however, is not daunted. Although the beating of the excised heart may be inexplicable by animal spirit theory, he believes that vibrations provide a ready explanation. This explanation involves the very ad hoc idea that the “fibers and blood globules” of cold-blooded animals possess “an electric or attractive virtue” not found in the higher animals.52 This “virtue,” he argues, causes the tiny particles in the cardiac muscle fibers of the relaxed heart to attract each other once more and the heart contracts once again. On contraction the vibrations are obstructed (as before) and the cardiac muscle relaxes. Thus the excised heart continues its rhythmical cycle of systole followed by diastole for some time after isolation from the rest of the animal’s body. It must be said that this explanation of the isolated heart’s movements seems very forced and rests on fanciful notions of “blood globules,” “attractive virtues,” and “disembodied heat.” But this is as far as Hartley’s Newtonian principles allow him to go in the mid-18th century. It was not until another two centuries had passed that the chemistry and physics of life had proceeded far enough for the beating of an isolated heart to be understood in ultimately Newtonian terms. This required an understanding not only of the molecular biology of muscle contraction but also of the biochemistry of pacemakers. These matters were far in the future. In Hartley’s century the living process remained at root a mystery. Into this void rushed numerous theories involving vital principles, especially those of Georg Ernst Stahl and his followers (see Chapters 10 and 11).

Vibrations and Associations We noted above that when Priestley came to edit a new edition of the Observations in the late 18th century, he omitted all the preliminary material on vibrations as “too difficult for the average reader.” Hartley’s fame rests on the psychological association theory. Yet, as Coleridge saw, this theory is firmly based on the application of vibrationist theory to the brain itself.53 There is no need to discuss this part of Hartley’s theory in detail in this book; it has been examined extensively in many other publications.54 In essence, Hartley believed that sensations, especially when repeated, leave behind small “vestiges” or miniature vibratory traces of themselves. He called these vestiges “vibratiuncles” and linked them to sensory memories or what he called “simple ideas of sensations.” Well ahead of his time, he even proposed that different sensory systems could have distinct places for their specific memories. Visual vibrations might, for example, leave vestiges in the “thalami of the optic nerves,” where these nerves seemed to terminate.

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Vibrations and Subtle Fluids These vestiges could account for simple memories, such as those that Newton wrote about in Query 16 of his Opticks (p. 347), where he described how moving a glowing coal in a circle gives the impression of a ring of fire. When describing this illusion, Newton wrote, “the motions excited in the bottom of the eye by the rays of light are of a lasting nature.” Hartley concurs, quoting Newton and writing that the inertia of the aetherial particles set in motion could account for this transient sort of memory. Repetition strengthens these vestiges or vibratiuncles, and we experience this as a strengthening and embedding of the memory. Hartley goes on to explain how complex ideas are built up by combinations of vibratiuncles and, finally, how different vibrations excite each other, thus explaining how one idea comes to be connected with another, thus providing a physiological basis for the association of ideas. Hartley’s vibrationist neurophysiology thus envisages the conscious brain as filled with a complex interweaving set of vibrations and vibratiuncles perpetually surging through the white matter. This ever-changing wave pattern forms the physical aspect of consciousness. It provides an early example of a dual-aspect identity theory, a theory that remains the default position of most modern neuroscientists. Hartley himself, as we noted above, was a devout believer and was in no doubt of the separability of mind and matter, but he does note, in both the Conjectures and the Observations, that “matter, if it could be endued with the most simple kinds of sensation, might arrive at all that (p.155) intelligence of which the human mind is possessed” [our italics].55 Hartley’s theory, despite his expostulations to the contrary, expostulations that failed to convince some of its more acute readers,56 plainly points towards a materialistic theory of the mind. Isaac Newton’s concept of aetherial particles was, as we saw, thoroughly materialistic. They were to be compared to the particles of which air and light were composed, although infinitely smaller. But even Newton retained the notion of an ill-defined “sensorium” in the brain to which the happenings in the world outside were delivered. Hartley had brought this sensorium to earth. It consisted of the white matter of the brain and spinal cord. The complex three-dimensional oscillations occurring in this homogeneous material formed the physical aspect of our day-to-day consciousness. There was no “sensorium” analogous, on an everyday scale, to the vast interstellar sensorium, which Newton conceived to be the sensorium of the Deity. Material vibrations explained all.

Demise of Vibrationism

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Vibrations and Subtle Fluids Hartley’s Newtonianism could not last. His Yorkshire friend, the Reverend John Lister, on receiving an advance copy of the Observations in 1747, wrote congratulating Hartley on a “very considerable achievement,” but added, somewhat acidly, that “the first part [that presenting the vibration theory]… seems to be built so much upon Hypothesis that I am apt to think it will give entertainment rather than satisfaction.”57 This, unfortunately for Hartley, seems to have been the view of most of his early readers, especially those trained in medicine. Herman Boerhaave, the so-called “Praeceptor” or “teacher” of Europe (see next chapter), held an anatomically informed version of the ancient neurophysiology of animal spirit. It is thus not surprising to find that, in the English translation of his widely read and highly influential Institutes of Medicine, he had issued a damning verdict on vibrationist neurophysiologies: There is therefore no face of truth in that Opinion, which asserts that Nerves perform all their Actions by Vibrations, like those which arise from striking a tense Chord or Thread: since this is repugnant to the nature of the soft, pulpy and flaccid Nerves which have so many inflections and incurvations.58 Although Boerhaave is probably referring to Swammerdam’s theory (we noted in Chapter 7 that he had made himself responsible for publishing his fellow Dutchman’s work in 1737), his strictures were widely seen as applying to all vibratory theories, including those of Newton and Hartley. He could not, of course, have himself been referring to Hartley’s Observations, as this was published some 11 years after his (Boerhaave’s) death. Later, however, Boerhaave’s skepticism was confirmed when his pupil, Albrecht von Haller (1708–1777), repeated it in his similarly influential Elementa physiologiae, which appeared between 1759 and 1766. This text formed the basis of physiological thought for a century. The thoroughgoing criticism of vibrationist neurophysiology was repeated once again in the 1786 English edition of his First Lines of Physiology, a similarly very influential text. He writes: That this [fibril] is a mere solid thread…has been asserted by many of the moderns;…when it is struck by a sensible body, a vibration is excited, which is then conveyed to the brain. But the phenomena of wounded nerves will not allow us to imagine the nervous fibers to be solid,…all the nerves, at their origin, are medullary, and very soft, and exceedingly far from any kind of tension…that the nerves are destitute of all elasticity is demonstrated by experiments, in which the nerves cut in 2 neither shorten nor draw back their divided ends to the solid parts.…Add to this, that the force of an irritated nerve is never propagated upward, so as to convulse the muscles that are seated above the place of irritation. This is a consequence altogether disagreeing with elasticity; for an elastic cord propagates its tremors in every way.59

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Vibrations and Subtle Fluids Boerhaave and Haller, however, seem to have misunderstood the Newton/ Hartley vibration theory. That theory never required nerves to possess “pianowire” tenseness. Indeed, Hartley as we noted above, was quite clear and emphatic that they did not. The wave-actions envisaged took place in the imprisoned aetherial particles, surging to and fro, like sound in the atmosphere, rather than vibrations in a solid object. But the damage had been done. The Newton/Hartley neurophysiology thus had very little influence on subsequent neurophysiological thought, whatever its influence might have been (and it was great) on psychology and philosophy.60 When Robert Caton discovered real evidence for the presence of vibrations, electrical vibrations, in the brain in 1875, he makes no reference to the work of any previous “vibrationist.”61 Hartley’s work, or that of any successor, is again nowhere cited in the papers with which Hans Berger initiated electroencephalography (EEG).62 Although the doctrine of animal spirit coursing along hollow nerve fibers was gradually being disproved by (p.156) new experiments and observations, the possibility that Newtonian vibration theory might form its successor proved to be a false dawn. The cutting edge of research was to be found in chemistry rather than in physics. It was to be found in the work of Hartley’s older contemporary Herman Boerhaave and his pupil Albrecht von Haller. These contributions will be reviewed in the next chapters. Nevertheless, it can be argued that vibration theory opened minds to new possibilities. Meanwhile, the true successor to the theory was being assembled elsewhere, in investigations of electric fish from the tropics of South America and in the electrical experiments of Europe and North America. These will be described and discussed in the last section of this book.

Concluding Remarks Clearly, vibration theory, despite its world-renowned champion, did not topple the time-honored doctrine of animal spirit. That well-entrenched doctrine still had many firm adherents. Vibrationism, moreover, lacked a vocal champion. Even Hartley was not inclined to promote it after his Observations came out, having more faith in the associationist psychology it was intended to underpin. Thus, even though the animal spirit hypothesis was in crisis, the vibrationist concept did not emerge as a strong challenger.

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Vibrations and Subtle Fluids Vibration theory thus effectively died with Hartley in the mid-18th century. He left no school of disciples, no continuing research program. The slow development of anatomical knowledge provided no more support for vibrationism than it did for the hydraulics of Descartes or the iatromechanics of Borelli. Indeed, the first of the great 18th-century dynasty of Edinburgh anatomists, Alexander Monro Primus, was scathing. He listed three pertinent objections to Hartley’s theory. Like others, he seems not to have read the Englishman’s treatise carefully and in his third objection wrote that “the nerves are unfit for vibrations because their extremities…are quite soft and pappy.”63 The mistaken belief that Hartley conceived nerves to vibrate, like those of a stringed instrument, seems to have been prevalent among neuroanatomists of the period, and his ideas, in consequence, came to be regarded as mere speculation. Moreover, the cultural landscape began to change. A reaction set in against the seeming aridities of Newtonian mechanism. “Pray God us keep,” wrote William Blake at the beginning of the 19th century, “From Single vision, and Newton’s sleep.” The mechanistic paradigm seemed increasingly inadequate to biological reality. It could not provide the looked-for successor theory to the animal spirit of the ancients. That successor theory turned out to come, as noted above, from a very different direction and from very different researches, directions and researches that will be discussed in the concluding chapters of this book. Nevertheless, to finish on a more positive note, one might argue that the Newton/Hartley vibration theory reflected a growing disenchantment with the received doctrine of animal spirit coursing down hollow nerves. Vibrationism did not require a site for manufacturing the spirit, nor a reservoir to contain it, nor hydraulics to distribute it, nor did it envisage muscles filling like balloons to bring about contraction. All of these requirements were being challenged by the work of anatomists and experimentalists. Newton and Hartley opened 18thcentury minds to the possibility of radically different alternatives. Notes:

(1) In Turnbull, 1977, Vol. 2, p. 289. The double-dating on 18th-century documents is due to the fact that until 1752 New Year’s Day in England was celebrated on March 25. Hence the early months of the year—January, February, early March—fell at the end of the old year or the beginning of the next depending on the calendar being used! There is also, of course, the matter of changing from the old-style Julian calendar (OS) to the new-style Gregorian calendar (NS), also in 1752, when the populace regretted apparently losing 11 days. These confusing issues are explained in the preface to Turnbull, 1959, Vol. 1.

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Vibrations and Subtle Fluids (2) Newton recognized this himself. “If I have seen further than others,” he wrote, “it is because I stand on the shoulders of giants.” (Letter to Robert Hooke, February 5, 1676. In Turnbull, 1959, p. 416). We have already noticed (Chapter 4) that this sentiment is not original with Newton. (3) Dijksterhuis, 1961. (4) Burtt, 1932, p. 237. It is, of course, a mistake to view Newton as if he were the first mathematical-physicist in the modern sense of that term. Worldchanging as his researches were in this area, modern historians have shown that he spent rather more time in alchemical and theological research and may, indeed, have regarded his physics as a distracting sideline. He was an altogether more complex character than depicted in most popular accounts. (5) Voltaire, 1738. (6) Algarotti, 1737. (7) See Feher, 1990. (8) Jacob, 1976. (9) See Fissell and Cooter, 2003. The importance of coffeehouses for the interchange of ideas in the 18th century has often been noted. In the middle of the century at least 500 such establishments were to be found in London alone. (10) Derham, 1714. (11) Paley, 1802. (12) Both Leibniz and Huygens found the idea of action at a distance very difficult to accept (see Dijksterhuis, 1961, p. 480). (13) January 17, 1693: in Cohen, 1958, p. 298. (14) The ancient atomic theory had been resurrected in the previous century by the Catholic priest Pierre Gassendi in 1649. Although Gassendi is normally accorded the honor of reintroducing atomism to the modern world, he was in fact preceded by an Englishman, Nicholas Hill, who published a tract actively supporting the atomism of Leucippus and Democritus nearly 50 years earlier, in 1601 (see McColley, 1949) and, earlier still, by the discovery of a manuscript of Lucretius’ great poem, De rerum naturae, in 1417, at the beginning of the Renaissance, by Poggio Bracciolini (see Greenblatt, 2011). (15) Albert Michelson and Edward Morley preformed their paradigm-changing experiment in 1897. It is generally regarded as providing the first strong evidence indicating that interstellar aether could not exist (Michelson and Morley, 1897). Page 21 of 25

Vibrations and Subtle Fluids (16) It is perhaps worth noting for nonscientific readers that the original and still scientific meaning of “elastic” is of a body that returns to its previous shape or bulk after deformation. The colloquial meaning—stretchable—has nowadays drifted somewhat from this precise definition. (17) In the Opticks (Query 31, pp. 372–3) Newton writes, “vis inertiae is a passive Principle…By this Principle alone there never could have been any Motion in the World…Some other Principle was necessary for putting Bodies into Motion; and now that they are in Motion; some other Principle is necessary for conserving the Motion.” (18) Letter to Oldenburg in Brewster, 1855, Vol. 1, p. 390. (19) Newton, 1713, Principia mathematica:.Scholium generale. (20) Galilei G 1623/2008, pp. 179–189. (21) Aranzi as early as 1595 seems to have been one of the first, if not the first, to remove the sclerotic from the back of the eyeball and to note the tiny inverted image (Polyak, 1957, p. 38), but the best-known demonstration is due to Kepler in the short book Ad vitellionem paralipomena, which he published in 1604 (Donahue, 2000). Descartes published another well-known figure in the Optics, which he appended to his 1637 Discourse on Method (in Cottingham, Stoothof, and Murdoch, 1985, Vol. 1, p. 171). (22) Newton, 1731, p. 12. (23) Newton, 1731, p. 12. (24) Ibid., Query 23. (25) Hales, 1731, Vol. 2. (26) Langrish, 1747, p. 31. These lectures originated a number of years previously when in 1733 Langrish published an Essay on Muscular Motion (Langrish, 1733). (27) Hartley is known to have attended classes in chemistry by the strongly Newtonian John Mickleburgh. Without formal training Hartley seems to have achieved sufficient medical knowledge by reading the available texts, and there seems to have been no complaint from the patients he subsequently treated. Indeed, we learn from his son, “He visited, with affectionate sympathy, the humblest recess of poverty and sickness, as well as the stately beds of pampered distemper and premature decrepitude” (Hartley jnr, 1791, p. ii).

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Vibrations and Subtle Fluids (28) Further biographical detail may be found in the Dictionary of National Biography (Oxford: Oxford University Press, 1975) and in Gillispie, C.C, 1972, Dictionary of Scientific Biography (New York: Charles Scribner). (29) Hartley, 1749. We have used the sixth edition published by Thomas Tegg in 1834. (30) Hartley, 1746. (31) Hartley, 1749, p. 604. (32) Later Coleridge became strongly antagonistic and, under the spell of German metaphysics, derided Hartley’s association psychology: “It is a mere delusion of the fancy to conceive of the pre-existence of the ideas in any chain of association as so many colored billiard balls in contact” (Coleridge 1817/1975, p. 63). (33) Priestley, 1775. (34) Coleridge, 1817/1975, pp. 63–64. Hartley is quite explicit at the beginning of the Observations: “vibrations should infer association as their effect, and association point to vibrations as its cause” (p. 4). Italics in original. (35) Brett, 1921; see also Smith, 1987. (36) Hartley, 1749, p. 4. (37) Newton, 1730, Query 21. (38) Hartley, 1749, p. 5. (39) Hartley, 1746, p. 11. (40) Hartley, 1746. (41) Hartley, 1749, p. 11. (42) Hartley, 1746, pp. 8–9. (43) Newton, 1730, p. 320. (44) Hartley (1749, p. 7) writes that he regards the terms “sensorium,” “fancy,” and “mind” as equivalent expressions. (45) Hartley, 1749, p. 8. (46) Hartley, 1749, p. 56. (47) Ibid., p. 56. Page 23 of 25

Vibrations and Subtle Fluids (48) Ibid., p. 56. (49) Ibid., p. 56–57. (50) Ibid., p. 57. (51) Ibid., p. 55. (52) Ibid., p. 60. (53) See Smith, 1987. (54) See Glassman and Buckingham, 2007; Oldfield and Oldfield, 1951; Marsh, 1959. (55) Hartley, 1746, General Scholium; 1749, Conclusion to part 1, p. 321. (56) Priestley, in the first of the introductory essays to his 1775 edition of the Observations, fully acknowledges the materialistic implications of Hartley’s theory: “I am rather inclined to think that…man does not consist of 2 principles so essentially different from one another as matter and spirit…[but that] the whole of man is of some uniform composition and that the property of perception, as well as the other powers that are termed mental, is the result [whether necessary or not] of such an organical structure as that of the brain.” Priestley is thus prepared to accept that “the whole man becomes extinct at death” and that we can only pin our “hopes of a future existence on the Christian doctrine of a resurrection from the dead.” (57) Trigg, 1938, p. 268. (58) Boerhaave, 1742-46, Vol. 2, p. 310. (59) Haller, 1768, p. 220. (60) It is interesting, however, to note that the Newton/Hartley theory did not fall completely stillborn from the press. At least one physiologist in the mid-18th century, Charles Nicholas Jenty, made use of the theory, though omitting its vibrationist core, in a three-volume text on human and animal anatomy and physiology (Jenty, 1757). Further detail may be found in Chapter 10. (61) Caton, 1875.

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Vibrations and Subtle Fluids (62) Gloor, 1969. It has, of course, to be remembered that neither Robert Caton nor Hans Berger was a historian, and they were publishing some 150 years after the publication of Hartley’s Observations. Nevertheless, if Hartley’s vibrationist neurophysiology had influenced “mainstream” neurophysiology, its presence, or that of its successors, would hardly have been overlooked by the two scientists who discovered that vibrations, albeit of an electrical nature, were indeed detectable in the human brain. (63) Monro, 1781, pp. 322–324.

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Animal Spirit in Action

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Animal Spirit in Action C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0010

Abstract and Keywords This chapter discusses the changes and elaboration of the animal spirit doctrine by the foremost biomedical thinkers of the 18th century. It reviews Georg Ernst Stahl's animistic ideas, which were inadequate and moved back to a more mechanistic physiology. It then introduces Herman Boerhaave, who is also called the teacher of Europe. The rest of the chapter focuses on Boerhaave's deep and detailed summary of early-18th-century work on the physiology and anatomy of the neuromuscular system. Finally, this chapter also reviews several relevant figures in 18th-century biomedicine and some electrical theories of the 19th century. Keywords:   animal spirit doctrine, biomedical thinkers, Georg Ernst Stahl, animistic ideas, mechanistic physiology, Herman Boerhaave, neuromuscular system, 18th century biomedicine, electrical theories

We chuse [sic] to call them by the Name of (πνευμα or) Spirit, after Hippocrates, who by that Denomination understood a Fluid capable of exerting considerable Forces, without being visible, like the Wind. Herman Boerhaave (1742–1746), Academical Lectures on the Theory of Physic, §291, note 1, vol. 2, p. 325

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Animal Spirit in Action Having reviewed the plurality of opinions that arose about the animal spirit during the scientific boom that characterized the 17th century,1 we are ready to examine how all of that was finally integrated and settled as an approximately standardized mature theory. This tendency to conciliate opposing views with an unshakeable confidence in the power of human reason, even if sometimes tricky and not always successful, was the essential quality that distinguished the “Siècle de Lumières” (“Century of Lights”), to use Immanuel Kant’s (1724–1804) descriptive term. Further, even more than in the 17th century, this period better known in English as the “Age of Enlightenment” was also very much an age of experiments and a time when reasoning inductively was valued more highly than reasoning deductively. As a result, it was an era during which many leading natural philosophers began to support their scientific theorizing with observations and experimental data. Nevertheless, particularly in the German-speaking countries on the European continent, the concept of the soul was not completely vanquished from the scientific picture. In fact, this metaphysical entity continued to reign supreme in some conceptions of physiology, no matter that nearly 60 years earlier Descartes had famously announced “That it is an error to believe the soul gives motion and heat to the body.”2 Hence, while there was in some circles a push to a more empirical and objective sort of science, one without allusions to metaphysical entities, in others the soul remained in charge of promoting and controlling every movement and biological process in the body. Heading such a position was Georg Ernst Stahl (1660–1734; Fig. 10.1), a professor of chemistry and medicine at the newly founded University of Halle in the also freshly established Kingdom of Prussia. The university, imbued with a strong Lutheran tradition and a quite conservative outlook, was a perfect place to foster Stahl’s brand of “true” medical thought.3 Let us briefly review the soul’s difficult task according to this system.

The Anima in Full Charge of the Body Stahl, who is probably better remembered today for his mistaken theory of “phlogiston” to explain combustion and for his studies of chemical transformations, was not, however, inspired any longer by a naïve religious belief but rather by a serious philosophical proposition. He accepted that there is no way for an incorporeal entity like the soul (anima) to interact physically with a material body, but insisted that this did not preclude it from having a conducting influence upon mechanical operations through an equally incorporeal mediator. This ad hoc intermediate agent is “motion,” as incorporeal as the soul itself, and yet having direction and speed.4 Therefore, through incorporeally modulating motion of all material particles in the body, the soul can fully govern the whole of physiology. Transfer of information or commands from some bodily parts to certain others, like from the sense organs to the brain and from here to the muscles, is consequently unnecessary. The animal spirit can thus be dispensed with entirely. Page 2 of 39

Animal Spirit in Action As a physician, Stahl acknowledged that the body is composed of many individual components, and that a subset of these parts is related to producing movement. He believed, however, that the elements involved represent no more than the machinery of motion, not the initiating source of the movements. Given this basic assumption, he considered it irrelevant to study the fine details of anatomy, because these were immaterial to the ultimate origin of movements. That is, the actions of muscles, nerves, and bones may be correlated with movements, but none of these relations is really causal. Any attempt to describe the components as they actually are and move was something trivial to Stahl, who was much more interested in understanding the manner in (p.158) which the original source (i.e., the soul) achieves its ends. He believed that mechanical approaches to physiology are blatantly misleading, because this mindset assumes that explaining how something happens is equivalent to explaining why it happens. Stahl saw this assumption as shortsighted, as one that stopped a step short of the fundamental issue. He felt that detailing no more than the parts of the body and their physical mechanisms would lead many to the conclusion that nothing else is involved in the process; and this, he states, is an illusion. How is not why, any more than description is not causation.

Figure 10.1: Georg Ernst Stahl (1660– 1734), a German chemist and physician at the University of Halle who fought hard to establish a “true” medical theory, according to which the soul directly micromanages all the bodily processes. In this influential new wave of animism in physiology, there is no need for intermediary specialized agents such as the animal spirit. (Line engraving dated 1715; Wellcome Library, London, cat. L0008079)

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Animal Spirit in Action Accordingly, Stahl went on to explain that the soul, or anima, is the source of all visceral movements vital to life; without the soul, the body cannot survive and it quickly decomposes. The same general principle accounts for all other actions of the body, but not in the Cartesian sense, whereby the soul controls involuntary and voluntary movements indirectly via the pineal gland in the brain. Instead, here the Stahlian soul is directly involved as the immediate and active protagonist in every volitional, reflexive, and vegetative aspect of the body, no matter how varied or minute. At the turn of the 18th century, with the European scientific community enthused with mechanics in the wake of Newton’s remarkable achievements, these views were sure to attract attention, and so they did, though not for applause in every case.

A Battle to Death and Beyond Gottfried Wilhelm Leibniz (1646–1716; Fig. 10.2), another German philosopher and scientist, was appalled by this whole reasoning, with the spurning of the animal spirit being one of his main concerns. In a private essay of which he arranged for Stahl to receive a copy, Leibniz exposed a series of “doubts” about the addressee’s claims: It surprises me that the distinguished gentleman moreover rejects vital and animal spirits, i.e., an imperceptible, swiftly flowing fluid in the body. For a correct understanding of the matter does not allow that there be no motive force in the body other than the soul.5 Stahl’s reply, also in private and in the convoluted Latin style for which he was notorious, did little more than stress his own views: I acknowledge and declare the soul as just such a principle provided with the faculty of moving energetically, for the reason that movement, act and effect also are, I say,

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Animal Spirit in Action (p.159) from every consideration and point of view something incorporeal, and by just this it is clearly demonstrated with respect to the nature of their efficient cause that this is too something incorporeal…. Therefore although the soul so carries out even her own proper business by means of movement that it is her first and inclusive power, which the others then follow in further progress; still those coarser and stronger movements induced in a body by however small things, follow.6

Leibniz’s response was emphatic, this time alluding to his own work: I have proved in a general manner the existence of the animal spirits, that is of a fluid that produces impulse. This proof comes from the fact that the body cannot be moved but by another body that is contiguous and already

Figure 10.2: Gottfried Wilhelm Leibniz (1646–1716), a prominent German philosopher, scientist, and diplomat who battled Georg Stahl’s brand of animism, being particularly incensed at its denial of the existence of the animal spirit. (Oilpainted portrait by J. Wentzel, around 1700; public domain picture freely available at http:// commons.wikimedia.org/wiki/ File:Gottfried_Wilhelm_Leibniz_c1700.jpg)

naturally in movement.7 Indeed, other than the mysterious property of magnets, direct contact was seen as a requisite for the transmission of kinetic energy (vis viva in Leibniz’s terms) from a moving body to another in mechanical systems, and a living body was no exception. We might recall here that a novel notion of action at a distance was then being proposed by Leibniz’s contemporary and rival Newton,8 but this is not an idea that the German philosopher would even consider. Although Leibniz’s death concluded this ongoing debate, his adversary went on to publish a book containing the succeeding stages of the exchange so as to remove any ambiguity about who was the clear winner.9 Still, Stahl’s supposedly last word on the matter did not go unchallenged.

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Animal Spirit in Action Smart Animal Spirit The next tug back toward a reasonable mechanistic physiology came from Friedrich Hoffmann (1660–1742; Fig. 10.3), a former friend of Stahl and a more senior member of the same faculty at the University of Halle, who took up the task of struggling against his now-despised colleague’s ideas and continued even after the animist author’s death. Hoffmann insisted on the basic mechanical premise that motion is a property inherent to matter,10 and that it has no separate existence apart from bodies. The latter are provided with a certain motive force and power of resistance, by which they act one on the other and by mutual action and reaction change their position and produce motion. This motion is the origin and cause of all phenomena, qualities, effects, life, nutrition, corruption, indeed of all changes in corporeal things.11 Hoffmann’s physiology was based heavily on his physics. In contrast to Stahl’s doctrine of the soul acting directly upon corporeal parts, he accepted the traditional view that animal spirit serves as an intermediary, being directed by the soul to produce specific functions in the body.12 This interaction is, however, complex:

The motion of the animal spirit is dependent on the proper mixture and motion of the blood and the humors; and the motions of the mind, its inclinations and thoughts, arise in proportion to the motion and proper mixture of the animal spirit.13

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Animal Spirit in Action Consequently, Hoffmann regards the animal spirit as closely related to the humors, including lymph, saliva, chyle, milk, bile, semen, and pancreatic humor, and it even enters into the composition of some of these fluids. Thus, for example, “Saliva consists not only of aqueous and very fine saline particles, but of very fine elastic particles brought through the nerves,” so it “depends on the blood serum and the (p.160) composition of the animal spirits.”14 Accordingly, the reader is

Figure 10.3: Friedrich Hoffmann (1660– 1742), a physician and chemist at the University of Halle like Georg Stahl, who also opposed the latter’s extreme animism. Hoffmann advocated a mechanical physiology in which animal spirit is involved in virtually all the fluids within the body, exerting its influence in different ways. Yet the source of vital motion is not the soul, which limits itself to provide timing and directionality to movement intrinsic to matter. (Oil-painted portrait by Baltashar Denner, 1726, now exhibited at the Hermitage Museum, St. Petersburg; public domain picture, freely available by courtesy of The Yorck Project: 10.000 Meisterwerke der Malerei

warned that some of these at http://commons.wikimedia.org/wiki/ relationships may be File:Balthasar_Denner_002.jpg) dangerous, even leading to contagious diseases. As a case in point, “The motion of disordered animal spirits can be communicated to the saliva, as is evidenced by the bite of a mad dog.”15 Looking more closely at the animal spirit contained in the nerves, Hoffmann describes it as “nothing but very fine matter, endowed with a limited mechanical power suitable for bringing about ideational and ordered motions in the body. Hence it can properly be called spirit.”16 He further tells us that it is “neither alkaline nor acid nor sulfurous,” and probably consists of two substances: “One, more moist, is from the very fine part of the nutritive juice; the other, more dry, is elaborated from the purer particles of the air, taken into the blood with the assistance of the lungs.”17 Given the stiff elasticity of these particles, the animal spirit “can be moved by tensile objects, and thus arise sensations which are only particular changes of the animal spirits and nerve.”18 These changes are brought about by objects that stimulate the senses, so that in general The instrument of all sensation, against which the object strikes, is a nerve or its extremity, which ends either in a membrane or in a papilla. Against this various objects press and excite varied motion. By means of the animal spirits this motion is transferred to the common sensory, where perception takes place.19

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Animal Spirit in Action An even more striking and remarkable feature of Hoffmann’s animal spirit is having a power impressed by God, not only of moving themselves mechanically, but doing so by choice, purposefully [determinate] and toward a definite goal. This power is called the sensitive soul, and it exists entirely in the most subtle fluid of the brain.20 Yet apart from its intentional directionality and timing, the fluid acts according to usual mechanics when it comes to moving the body: “As air shut up in a bladder, when expanded, can raise great weights, so also the muscle fibers, expanded by the force of the spirits, cause the bones to move, by means of the tendons.”21 Hoffmann’s conceptions in this regard are therefore something of a mix between Stahl’s view of the soul consciously acting everywhere throughout the body, on the one hand, and the traditional model inherited from antiquity in which the animal spirit serves as an instrument of the soul, on the other. Once again the difficulty faced earlier by Descartes demanded an approach that would permit a separate and non-mutually obstructive study of soul and body. A total demarcation between both spheres, if only for practical purposes, was the answer proposed by a younger contemporary of Stahl and Hoffmann.

The Shaping of a Befitting Mind The son of a Dutch Reformed Church pastor, Herman Boerhaave (Fig. 10.4) was born not far from Leiden on New Year’s Day in 1669 and lived well into the next century, dying late in 1738. He would become the most prestigious teacher of medicine in the early 18th century, but not before having followed a somewhat tortuous intellectual path that is worth summarizing here as a background for better grasping his peculiar mindset.22

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Animal Spirit in Action (p.161) At first Boerhaave thought he would follow in his reverend father’s footsteps, and so he studied theology as well as the classics, history, and their chief languages (e.g., Latin, Greek, and Hebrew). Pursuing his chosen career for the ministry, he matriculated at the University of Leiden and took a degree in philosophy in 1690, selecting “the distinct natures of the mind and body” as his thesis subject. Eventually, however, he decided to study both of those natures, in part as a means to having a greater professional security, since the mixing of theology and medicine was then fairly common, with clergymen attempting to heal bodies while also saving souls. Oddly, the young Herman did not attend many medical lectures as a student, preferring instead to learn theoretical medicine on his own, starting from the beginning with Hippocrates and the ancients. He did, however, go to some anatomical demonstrations and did his share of animal dissections, being then especially drawn to medical chemistry. At last he gave up the idea of an ecclesiastical career, although always remaining deeply interested in

Figure 10.4: Herman Boerhaave (1668– 1738), a leading chemist and physician based at the prestigious University of Leiden in Holland, who became the respected teacher of the more relevant natural philosophers and physicians in the 18th century, and therefore one of the most influential figures in the history of medicine. He incorporated mechanistic accounts on the roles of the animal spirit and other spirits in his widely read treatises on chemistry and medicine, thus ensuring the mature theory of spirits to prevail through most of the 18th century —to the dismay of not a few critics. (Line engraving by F. Anderloni after an original portrait by G. Garavaglia; Wellcome Library, London, cat. V0000624)

theology. In 1701, after having started a private practice, he was appointed lecturer in medicine at the university.

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Animal Spirit in Action Boerhaave would stay at Leiden for the rest of his life, where he would wear several coveted gowns and teach a variety of subjects, some in the large lecture hall and others at the Caecilia Hospital, additionally using the medical gardens to teach botany. Eighteenth-century natural philosophy, seeking to strike a balanced view and an eclectic synthesis (wherever possible) of the many new different and conflicting ideas about how things in the world—the human body and living things in particular—are organized and function, is best represented in his work. He had a sharp analytical mind and a flair for systematizing knowledge, both ancient and new, as well as a clear style of expression. Furthermore, his biological thought was intimately tied to the most advanced theories in chemistry, a science in which Boerhaave also became a leading expert. These talents made him a great teacher whose fame soon spread throughout Europe, and consequently his lectures were attended by many of the brightest young minds in the Continent. Almost 2,000 Dutch and foreign students matriculated in medicine while he was at the Leiden faculty, out of which 178 received degrees directly from him. In addition Boerhaave was a prolific writer. His many books, a number of them published in several editions and translated into various languages, made him one of the most widely read scholars of his age.23 At heart, however, the theologian in him stayed all along, and thus he devised a clear-cut approach to keep a sound intellectual balance.

Divide and Win In line with the subject of his thesis on philosophy, Boerhaave, unlike his countryman Baruch Spinoza (1632–1677), who viewed mind and body very much as one and the same thing,24 tried hard to keep the spiritual apart from the material.25 He flatly refused to enter arguments of this kind, stating that considerations about the human body as a metaphysical entity or as mind “do not at all come under the Province of the Physician.”26 He took to heart the common name applied to medicine at the time, “physick” or “physic” (from which the English word “physician” derives), to stress the fact that it dealt with the natural (physical) or material part of man.27 The term meant the study of the human body and its functions in order to understand it and heal the apparatus when faulty (i.e., just as we now refer to basic “medicine”). On the other hand, although physicians often acted also like counselors, as mentioned above, the professional treatment of all soul matters, both normal and abnormal, was best reserved to theologians and priests.28

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Animal Spirit in Action Consistent with this position, Boerhaave, basically a Cartesian, drew a clear dividing line between mind and physiology. Hence, such faculties as intellect, reason, or memory were left out of his analysis, not because they were unimportant or uninteresting in themselves, but because they are beyond the realm of natural science. The rest can all be explained in terms of biology, which rests on chemistry, which in turn is based on physics, from a perspective that we would now call utterly “reductionist.”29 The very title of one of his relatively early works indicates the groundbreaking comprehensive scope of Boerhaave’s approach to understanding and teaching medicine: A Method of Studying Physick. Containing What a Physician Ought to Know in Relation to the Nature of Bodies, the Laws of Motion; Staticks, Hydrostaticks, Hydraulicks and the Proprieties of Fluids; Chymistry, Pharmacy and Botany; Osteology, Myology, Splanchnology, Angiology and Dissection; the Theory and Practice of Physick: Physiology, Pathology, Surgery, Diet, &c. (1719). This broad scientific outlook was complemented with rigorous attention to data produced by observation and experimentation, as opposed to pure speculation. The human mind left to its own internal devices is notoriously unreliable, taught Boerhaave’s Calvinist creed, since it is in a fallen state and too corrupted by sin as for having a correct reasoning. A systematic critical comparison of our thoughts with what a careful look at the world outside shows is the only relatively safe method for arriving at right conclusions. In Dr. Boerhaave’s Academical Lectures on the Theory of Physic, edited by his talented student Albrecht von Haller and published in English from 1742 as “a Genuine (p.162)

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Animal Spirit in Action Translation of his Institutes and Explanatory Comment” (Fig. 10.5), we read:

He that desires to learn Truth, should teach himself by Facts and Experiments; by which means he will know more in a Year, than by Abstract Reasoning in an Age. Proper Experiments have always Truth to defend them; also Reasoning join’d with Mathematical Evidence, and founded upon Experiment, will hold equally true; but should it be true; without those Supports it must be altogether useless.30

Figure 10.5: Title page of Herman Boerhaave’s Academical Lectures on the Theory of Physic, from the volumes of which most of the quotations included here were taken, being an English translation of the celebrated Institutiones medicae, with “Explanatory” editorial comments (first volume, published in 1742).

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Animal Spirit in Action Boerhaave’s teachings are of special interest to us here for three main reasons. The first is that his work integrated the chemical and medical knowledge produced during the scientific revolution of the 17th century into a basically coherent system, which was largely accepted as standard theory by most natural philosophers throughout most of the 18th century. What Boerhaave taught could perhaps be questioned or even challenged, but not ignored, in any serious scientific, medical, or philosophical debate. Second, many of the important figures in the story of animal spirit throughout the 18th century were either his direct disciples or indirectly influenced by him to a considerable degree. Last but not least, he conceived of all living bodies—be they human, animal, or vegetal—as complex hydraulic apparatuses largely composed of vessels in a wide variety of calibers, all carrying fluids of various classes. These conduits range from large ones, such as arteries and veins, to microscopic and hence almost invisible ones, like those of nerve fibers. The animal spirit is one of such fluids and therefore just a specific instance within a more general, and highly influential, scheme. In the remainder of this chapter we review the physiology of the animal spirit, and a bit of its pathology, at their zenith in the early decades of the 18th century as they were expounded by Boerhaave, one of the staunchest crusaders of the theory, and a few other supporters. Not everyone agreed with this leading-edge scientific explanation of nerve function, of course, so we will also take a look at the competing views of some of its detractors. The reader is kindly asked for leniency toward the lesson-like tone in this part of our book, a reconstruction built by drawing from different works written by Boerhaave, which is aimed only at presenting a summary of our main subject the way a medical student probably would have written it in Leiden at around 1730.

Nature and Origin of the Spirit In purely physical terms animals and plants, just like all natural bodies—says Boerhaave31—are ultimately made up of diverse types of elementary corpuscles or atoms, which can be found either firmly associated with each other to form solid anatomical parts, or in a fluid state as humors and juices. Chemically, though, animals like plants consist for the most part of spirits, salts, oils, and simple earth. Spirits, therefore, constitute an entire chemical class ranging from the Spiritus rector, “a kind of Aura, or Vapour” that provides individual identity to a particular body, all the way down to common volatile liquids like alcohol and liquors. In fact the term “spirit” is often used by Boerhaave as a synonym of alcohol or liquor, occasionally even in the same paragraph.32 Accordingly, animal spirit is in this context definitely (p.163) a juice,33 as William Croone would have it,34 although a very special juice indeed as judged from its properties.

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Animal Spirit in Action Several lines of evidence indicate that animal spirit is an extremely thin and swift fluid. These indications are (1) its celerity of action, for an arm or leg responds instantly to the intention of raising it; (2) its quick evaporation, leaving little or no residue; and (3) the fact that it can flow within the exceedingly narrow vessels of the tiniest insects, small embryos, and even the animalcules that pullulate in semen. Thus this fluid is obviously quite different from any saline or oily matter known. “’Tis [sic] rather more probable,” concludes Boerhaave, “that this Juice or Spirit of the Brain and Nerves is like those of the most subtile and pure Water.”35 In turn this assumption leads to certain suppositions about its submicroscopic constituents, which necessarily have to be the most diminutive corpuscles of any circulating in the body. Animal spirit must therefore consist of “the most simple, dense or firm, subtile and moveable,” bits of matter, most probably spheroidal particles after being polished by frequent passes once and again along incredibly narrow ducts.36 For, just like any other humor in the body, the animal spirit proceeds from blood that has passed “thro’ many Degrees of Attenuation” (i.e., stages of progressive filtration) as it flows through a long succession of vessels of diminishing calibers, “till its parts become small enough to pervade the last Series of Vessels in the Cortex, and then it becomes the subtile Fluid of the Brain and Nerves.”37 Good scientists are always ready to modify their views whenever a discovery forces them to reject a seemingly established concept, no matter for how long that concept has been a part of accepted theory, particularly if the new finding reveals a gross mistake. Accordingly, following Vesalius’ recognition that, in contrast to bovines, the human brain has no rete mirabile38 (i.e., a vascular plexus where according to Galen the vital spirit [pneuma zootikon] was refined to become animal spirit [pneuma psykicon]39), this process has now been moved upwards and located in the brain substance itself, specifically in the cortex.40 “This Liquor being very subtile,” says Boerhaave, “perfectly simple, fluid and volatile, is therefore termed the Spirits of the Nerves, which are, from their Offices, distinguish’d into natural, vital, and animal, as we shall see hereafter.”41 It is the third class of “spirits”—the animal spirit—that is secreted in the brain cortex and controls the “animal” (i.e., governed by the anima or voluntary) faculties. Vital (involuntary) functions, on the other hand, depend upon the correspondingly named spirit that is most probably produced through an analogous process in the cerebellum. Finally, natural spirit, in contrast to the other two classes, arises at no particular organ but from the thinnest vessels in many different places, and instead of sensory or motor roles it serves to nourish and repair the smallest structures throughout the body.

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Animal Spirit in Action Boerhaave replies vigorously to several objections thus far raised against the idea of animal spirit, starting from that which points out the lack of any visible proof of its actual existence.42 This juice cannot be demonstrated to the eye, retorts our author, only because there is no instrument capable of showing it, just as no one could demonstrate continuity between arterial and venous capillaries before van Leeuwenhoek created his wonderful microscope lenses. Likewise, no one should be surprised that nerves do not swell if a ligature is applied to them, as someone might expect if a fluid is moving within, just as “no one could ever demonstrate the swelling of a lymphatic Artery by Ligature, when it is notwithstanding a real Artery, and an infinite Number of times larger than any of the nervous Tubuli.” Boerhaave admits as true that no content seems to come out from a nerve when its cut end is subject to negative pressure (i.e., suction) in an air pump such as those used by Robert Boyle. “But,” he responds, “suppose the Juice of the Nerves as gross as the common Air, do you think that Air could be perceived issuing out of the Body in an exhausted Receiver; but the nervous Juice is probably finer, more pellucid and less visible than the Air.” Still worse is to confuse—as did, to Boerhaave’s consternation, “the honest and otherwise judicious Malpighi and Bellini”—the subtle spirit of the nerves with the “the very thick, viscid, and lymphatic Juice which issues from the Nerves of an Ox Tail that has been cut off.”43

Circulation and Amount of Spirit As just mentioned, the animal spirit proceeds from blood that has been highly filtered through “the last Series of Vessels in the Cortex.” These utmost thin vessels are seemingly continuous with the myriads of delicate “tubuli” located in the “white, dry, and compact Substance” called the “medullary Part” of the brain —that is, the region situated just below the “external, ash-colour’d, soft, and moister Substance” termed “the cortical Part,” where numerous layers of vessels of ever-decreasing diameters lie at every successive stratum inward.44 Accordingly, the highly purified part of the blood that flows through the narrowest vessels in the lower levels of the cortex “is thence propell’d from every Point thro’ these Tubuli into the Medulla oblongata” (p.164)

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Animal Spirit in Action in the brain stem, where it is collected to be delivered through the nerves to diverse parts of the body as necessary.45 Boerhaave summarizes the forward part of this trajectory as follows (Fig. 10.6):

So that every moment a Person is alive and well, the Blood is impell’d from the Heart to the Cortex of the Brain, and its thinner Juices being attenuated in their Passage thro’ the several Series of the Vessels in the cortical Fabric, are at last transmitted in the Form of a most subtile Liquor into the medullary Tubuli; from whence it passes in an uninterrupted Course into every individual Part of the Body by the Nerves.46 Now, just like other fluids composing the blood, most of the animal spirit juice eventually gets back to the heart, and in this case it is next taken from here again “to the Spring from whence it came, to wit, the Brain.”47 The notion of animal spirit circulation seems to have originated with Boerhaave’s countryman Henricus Regius (1598–1679), who observed bubbles moving externally from the tail to the head over the body surface of a garden slug, and apparently related this phenomenon to the circulation of the blood.48 The returning phase of animal spirit can be completed along two partly different routes (Fig. 10.6), the actual pathway depending on (1) whether the nerves fuse with ducts embedded in the walls of hollow organs and pour the spirit into these organs as a lubricant vapor to “prevent their Concretion;” or (2) whether the channels become progressively ramified down to the minimal possible caliber, and then anastomose or connect again to become continuous with the macroscopic vessels involved with the venous return. In each case the recurrent trajectory includes pellucid and lymphatic veins, which pick up the spirit, and then larger vessels that lead up to the heart.49 A small fraction of animal spirit does not get back to the heart and therefore neither to the brain, but is exhaled through the skin “every way forming a spirituous Transpiration, as we know there is an arterious one.”50

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Animal Spirit in Action Thus the total amount of animal spirit remains fairly constant, as is also the case with the total blood supply to the body. Further, two main considerations suggest that the amount of animal spirit must be sizable. First, it is evident that the nerve tubules or fibers receive a continuous flow of spirit from the medulla, because ligation or injury of the nerves immediately abolishes all their normal actions. Furthermore, this consequence also proves that the animal spirit is the agent that performs all nervous functions.51 In addition, if the dimensions of the nerve fibers or tubules are compared with the bulk of the whole encephalon, it is easily realized that the number of fibers there has to be unimaginably huge. Since a large proportion of these fibers is usually at work in diverse nervous functions, this implies that a “vast Quantity of Juice forcibly propell’d hither must inevitably keep those Tubuli constantly open and full for Action.”52

Figure 10.6: Circulation routes of animal spirit in the body, according to standard medical theory in the 18th century as taught at the school led by Herman Boerhaave. Just like with any other physiological factor, the original source of animal spirit is food arriving from the stomach into the intestine (bottom), where the nutrients become chyle that is next taken up by the lacteal vessels into the liver, where the fluid’s contents are finally concocted into blood. This fresh new blood gets mixed with the rest already in circulation, as the whole is taken via the vena cava from the liver into the heart, which immediately propels the bulk of liquid into the network of arteries and arterioles that branch progressively along the vascular system (left). The blood is thus forced to flow through increasingly fine capillaries on its sinuous way from arteries to veins (top), along two possible routes. Most of the blood is carried back to the heart via the venous return (center), but the subtlest part of the liquid (animal spirit) is strained through the finest capillaries that connect with the medullary tubuli in the brain, and hence passes from the blood into the nervous system (right). Animal spirit is first collected within the “medulla oblongata,” then sent over as required to various destinations via the spinal cord and the nerves, and eventually makes its way to lymphatic vessels that ultimately drain into veins. Thus, just like circulating blood repeatedly returns to the liver and the heart, so nearly all of the circulating animal spirit returns sooner or later to its source in the brain. A small fraction, however, is lost by transpiration through the skin (right).

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Animal Spirit in Action Hence the nerve or animal spirit is kept continuously in motion, driven by the pulsations of the heart and the elastic (p.165) contractions of the arteries, both forces contributing to propel the fluid along its circular path throughout the body. Yet we should not imagine this movement to be fast or violent under normal conditions. In fact, the long and tortuous microscopic network, composed first of extremely narrow blood vessels with numerous bends and twists, and then of even finer nervous tubules in the medullary part of the brain, presents a formidable resistance to the thrusting power of the heart and the arteries. Therefore the fluid is actually strained through this network, so the impetus and velocity of flow in the brain are both reduced to much less than in any other vessels in the body, becoming in fact “constant, gentle, and equable.”53 It must be noted, however, that some decrease in the total quantity of animal spirit may occur under certain circumstances. Thus, for example, “Too little Sleep or over-watching consumes the Spirits, which can no otherwise be repaired than by Sleep.”54 This strict dependence of spirit levels upon sleep is presumably due to the fact that diminished awareness or unconsciousness entails reduced sensory stimulation, and therefore a lower level of activity of the whole system (see below), which can thus relaxedly replenish the store of spirit within the “medulla oblongata” (as it was then defined).

System Malfunction and Treatment As happens with other body humors, marked alterations in the speed of movement of the animal spirit can be detrimental to health, simply because it is involved in a wide variety of physiological processes. In fact, an “Excess or Deficiency in the Motion of the Spirits of the Nerves is more especially dangerous, since from thence all the digistive [sic] Powers, Secretions, and Excretions are disturbed or injured, so as to produce different Disorders almost of every kind.”55 Thus, for example, “to instance only an irregular Motion of the animal spirit differently varied, may produce, maintain, and increase a great Number of Diseases, with various Symptoms,” for The Spirits direct or govern all the Sphincters and Anastomoses throughout the whole Body, whence follow an infinite Number of Disorders from a Disturbance of the Spirits. Hysterical Women often become paralytic or apoplectic from slight Passions.56 Nevertheless, those multiple or generalized effects from the same cause do not support claims “at all times cried up, and especially by the Chemists,” that a single remedy can be effective to treat all diseases. It is true that all these Disorders lie in the same Humour, and the Physician cures them with Opium; yet it cannot be thence justly concluded, that therefore Opium will cure all Diseases: the nervous Juice or Spirit is indeed the Governor of the whole, yet it cannot from thence be esteemed always a Panacea, according to the Opinion of Dr. Phelips, Physician to the Prince of Conde.57 Page 18 of 39

Animal Spirit in Action It can therefore be concluded that “many Diseases are often removed by one Remedy, but never all Diseases.”58 That said, it could then be accepted that “the Remedies hitherto known to be more universal, are Water, Fire, Mercury, and Opium.”59 Experience had shown, for instance, that “most chronical Diseases arise from Obstructions; but Obstructions so far as they are such, all give way to the Power of Mercury.”60

Message-Conveying by Animal Spirit It is perhaps needless to point out here that the above-mentioned slow circulation of the animal spirit has little to do with the actual nerve functions involved in instantaneous sensory perception and muscular movements. The animal spirit must be circulated as a routine, ongoing maintenance process to keep the nerve fibers always full, fresh, and ready to respond to stimuli or motor commands. A much swifter, different kind of spirit motion is obviously required, for example, for having a protective hand raised to the face as soon as the eyes report to the brain that a potentially damaging object is fast approaching. And the same, of course, can be said of running, dancing, fencing, and other complex exercises and sports. Animal spirit transmits sensory and motor signals through a subtle movement comparable to the instant end-to-end transmission of a scratching sound along the trunk of a fallen tree, perceivable only when applying the ear to its surface. More illustrative is the following example inspired by an experiment attributed to the physicist Christian Huygens (1629–1695): Let a thousand polish’d Ivory Balls be placed in a hollow Tube fifty Feet long; if now the first of these is struck forward, at that very instant of time the last of them will depart from the last but one, while the intermediate ones are at rest. In this Experiment all these intermediate Spherules must have changed their spherical Figure by the Impulse, and recovered it again in so short an instant of time, except the last, which flew off from the rest, as having no other to resist it. Hence therefore the most hard Bodies in a very small Compass may propagate Motion ad infinitum.61 Now, as noted above, there are significant reasons to think that the corpuscles of animal spirit may be the most “dense or firm” in the body, so it is likely that they will behave the same way as ivory balls. Accordingly, the Boerhaavian animal spirit corpuscles do not have to be actually displaced in order to carry messages or commands; they do not even (p.166)

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Animal Spirit in Action have to oscillate like the “Motions backwards and forwards of the small Particles” that constitute the vibrations conveying sensory impressions, in the theory advanced by David Hartley a few years later upon premises postulated earlier by Newton.62 On the contrary, it is likely that the animal spirit corpuscles efficiently transmit nervous impulses while staying virtually static in their positions (Fig. 10.7).

Once we know how the nerve signals are propagated, it will be easier to understand how such signals participate in the perception of, and response to, stimuli. Yet explaining this requires a brief summary of the pathway involved in these processes.

Figure 10.7: Swinging metal balls illustrate the physical principle by which motion can be instantaneously transmitted along nerves by a succession of compact particles of animal spirit, according to Boerhaave. The impact of a ball knocking the second of the series on the left at once shoots out the last one on the right, with the intermediate balls scarcely moving, if at all.

Sensation and Perception Basic anatomy shows that the nerves involved in all forms of perception “descend” from the brain to the corresponding sense organs. Thus, writes Boerhaave, the optic nerves are “truly a Production” of the brain,63 so “the Image of the visible Object falls upon the Medulla itself of the Brain.”64 He explains that “as the mucous or soft Pulp, namely, the Medulla of the optic Nerve, is seated directly in this Point [the retina, where the entering image is ‘painted upon’], under the Pupil and crystalline Lens; this is evidently the Part which receives the Pictures of the Objects, and conveys by its continuity the Impression of the Image to the common Sensory, so as to excite in the Mind an Idea of the thing seen.”65 In an accompanying note we learn that: “There, that is in the Medulla of the Brain itself, the Mind sees, and not the Eye, as Aristotle justly observes. But,” Boerhaave continues in keeping with his above-described philosophical position, “it is not the Business of a Physician to enquire what Vision is in the Mind, only he is to know what it is in the Eye.”

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Animal Spirit in Action Similarly the “soft auditory Nerve,” after passing out from the encephalon through several slender channels, finally forms “a soft pulp into the Vestibulum under the oval Membrane: From all of which it is evident that the sonorous Rays by the trembling of this Membrane are conveyed” to the mind.66 The olfactory nerves, in turn, descend straight from the brain through the bone and get distributed over a large surface, “so that within our Noses the naked Substance of the Brain lies exposed.”67 All of these different “impressions” consisting of “a Change in the Surface of the Nerve, excited by the contact of the moving Object,”68 will be relayed directly to a collective receptive center, the “common Sensory” (Sensorium commune). It is at this ill-defined intra-cerebral location, aptly described in today’s terms as “the central switch in the ‘machina nervosa’,”69 where the “impressions” received by the sense organs excite “ideas” about the thing seen or heard (see below). These ideas become differentiated depending upon several factors, such as (1) the type of object causing the impressions; (2) “the particular Fabric”—that is, the histological organization as we would now say—of the sense organ involved; (3) the kind of nerve affected; and (4) “the different Part of the Medulla of the Brain from whence the nerve comes.” Indeed, according to Boerhaave’s opinion, “it seems probable, that each Set of Ideas dwell at the Origin of each particular Nerve in the Brain; those of Sound about the Origin of the auditory Nerves; those of Light about the optic Nerves, &c.”70 He further reasons that the “common Sensory” must be “near to the Seat of Life and the Mind,” as is suggested particularly by smelling, for fainted people show an immediate awakening reaction to a proper medicine brought up close to the nose.71 More specifically, the common Sensory seems to be seated where the ultimate lymphatic Arteries in the Cortex of the Brain first unite themselves to, and fill the beginning of the Nerves with Spirits throughout all the Ventricles and inequalities of the Brain, &c.…But the Territories or Limits of this common Sensory seem to be very large and various, so that each Nerve seems to have its particular Part in the Brain where those Ideas dwell which were conveyed by the same; the Ideas of Odours about the Termination of the olfactory Nerves; of Colours about the endings of the optic Nerves, and of Motion about the Nerves subservient to the voluntary Muscles, &c. In this Part it is that the great Commerce betwixt the Body and the Mind seems to be placed.72 Yet so far we have just part of the explanation for sensory physiology, since the

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Animal Spirit in Action Change only in the [sense organ] Nerve is not sufficient to produce Sensation; but it is farther required, that the same Change be propagated through a free Nerve to some Part in the Medulla of the Brain, and from every single (p.167) Nerve to a corresponding particular Part in the Medulla of the Brain; and this we learn from Ligatures, Wounds, and Corruptions of the Nerves and Brain.73 The actual mechanism involved in propagating the change is given in a brief note, where he advances a tentative answer to the question and concludes the matter with a confession: If it be asked, What Change is made in the sentient Nerve; I answer, that the Spirits propel forward those which lie next adjacent; and these again move the next, till the last but one moves the very last; and therefore the Change in the common Sensory can be nothing more than a Repulse of the Spirits against their Origin. This is certainly a very simple Explanation, but we know not of any other.74

Muscle Action Sensations sometimes have consequences that may be manifested as different actions or as no overt response at all. This variability in the response results because, when the impressions received by the sense organs arrive at the common sensory and become ideas, these may provoke in the mind either joy or sadness, or neither of them. Accordingly, the sensory message can cause love, hatred, or indifference toward the object eliciting such ideas.75 “But we are so framed,” continues Boerhaave, “that this Condition of the Mind either of Love or Hatred is apt to excite such muscular Motions in the Body.”76 And, just as the spirit of the nerves carries sensory impressions to the common sensory in the brain, so too “these muscular Motions are excited by means of the Spirits or Juice of the Nerves, propelled from the Brain into the Muscles.”77 These considerations have an interesting implication. The “common sensory” receives impressions transmitted by the nerves from all over the body, and in turn dispatches motor commands to all muscles subject to the control of the will, which are also distributed virtually everywhere around the organism. The astounding number of connections required to link all these in-and-out nervous pathways simply cannot be contained in a receptacle that is below a minimal size. It is therefore evident that the seat of the mind just cannot be the smallish “pineal Gland, as Cartesius would have it.”78

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Animal Spirit in Action In a separate long section Boerhaave discusses the difficult problem of muscle physiology.79 Here he deals with a major obstacle posed by sheer anatomy. The actual distribution of nerve fibers in a muscle is almost impossible to ascertain because our sense of vision, even in the case of “the armed Eye of Lewenhoec [sic],” lacks the power for perceiving the finest fibers inside the muscular mass. Nevertheless, based upon careful observations by several leading anatomists,80 who described nerve terminals expanding as a soft membrane in the skin and other organs of the body, it is highly probable, explains Boerhaave, that the individual nerve fibers expand also within every innervated muscle. Therefore, he postulates that the muscle fibers themselves “are a very fine Expansion of the ultimate Extremities of the smallest Nerves, deprived of their coats, hollow internally, and of the same Figure with the Muscle…being filled with Spirits or nervous Juice.”81 And this most likely interpretation means that everything which either perceives or moves in the Muscle, belongs only to the Nerve: and therefore every Muscle, so far as it is an Organ of Motion, appears to be a Continuation of the Brain, Cerebellum, and spinal Marrow; and that there is a continual Flux of nervous Juice from those Springs, namely, the Brain, Cerebellum, and spinal Marrow, into every point moving the Muscle.82 Next Boerhaave explains that the animal spirit proceeding from the brain supplies only voluntary muscles, whereas the involuntary ones receive vital spirit from the cerebellum. The question may then be posed of how does he account for reflex responses, which frequently involve otherwise voluntary muscles even when these are not at that moment commanded by the brain. This problem is, in fact, addressed by considering that “While the Will remains undetermined, all the voluntary Muscles remain equally full in all their Vessels, and equally disposed for Motion by the Blood and Spirits.” Accordingly, it can thus happen that “The Limbs being bent by an external Force, even against the Inclination of the Will, causes the flexor Muscles to put on the State of contracting or shortening in the same manner as if they acted by their own proper Motion, only with a less Force.”83 Although Boerhaave does not elaborate further on this point it is clear that nerves, like the will, do not participate in this phenomenon. It should therefore be inferred that at least the flexor muscles could respond directly to stimulation —that is, with a nerve-independent activation of their intrinsic capacity for contraction, as had been recognized since Galen and more recently investigated by William Harvey and especially Francis Glisson.84 But there is reason to surmise that Glisson’s work may have made Boerhaave somewhat uneasy (see below), so probably he preferred leaving this subject at that point.

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Animal Spirit in Action Another instance of voluntary muscle action apparently independent of the will occurs in automatic movements, “which operate only from Custom by the Influence of the Mind, of which by continued Use we are insensible; which Muscles taking their first Action from the Command of the Will, do nevertheless afterwards continue to operate in a manner as if it was spontaneously.” It is therefore unawareness of willed actions, rather than unwillingness, that takes place, for example, while we “walk at the same time that we are thinking upon divers Affairs.”85

(p.168) Mechanism of Muscle Action All things considered it seemed plain to Boerhaave that, whatever might be the cause of muscular motion, the muscle must dilate, fill, and alter the membranes of its fibers, so “as to reduce them from an oblong to a rounder Figure, increasing their smaller Diameter, and diminishing their larger, so as to bring the Tendons nearer to each other.”86 It was also apparent to him that such cause must necessarily come from the brain, the cerebellum, or the spinal marrow. Thus, he reasons, it “can be no other than a very thin fluid Body, very easily or quickly moved, and that it must be forcibly thrust into or applied to the Muscle.”87 Only the “nerve Liquor” or animal spirit satisfies all these requisites, and it is not “difficult to understand its Manner of Action.”88 A different puzzle was how to account for the obvious capability of the muscles to move sequentially at appropriate times, not all of them synchronously, even though nerves connected to the sources of spirit permanently supply all. The explanation Boerhaave gives is that the expansion of a flexible container by an influx is directly proportional to the quantity of fluid injected, and inversely proportional to the resistance offered by adjacent bodies.89 The quantity of fluid being poured, in turn, is greater when the flow is swifter. Consequently, the faster the spirit moves through a given nerve, the larger will be the dilation of a muscle at its end. Further, the motion of this muscle will be stronger if nearby muscles receive the spirit or nerve juice relatively slowly, and are therefore comparatively relaxed. As a corollary, complete rest or inactivity will follow an equal distribution of nervous juice to all the muscles of the body. But, replies Boerhaave in anticipation of the obliged question, “If you enquire after the Cause which produces this greater Celerity of the nervous Juice at pleasure, I must openly confess my Ignorance of it.”90

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Animal Spirit in Action Such a confession did not prevent him from then going back, just a few pages ahead, to this enigma of spirit physiology situated at the center of the mind–body problem.91 There seemed to be no doubt that the power increasing the celerity of the juice or spirit in a given nerve was the mind, or that the origin of the movement is inside the brain. One could even be reasonably sure about the specific part of the brain involved, for all the evidence suggested this was the common sensory—that is, the frontier between the ultimate and finest arteries and the beginning of the medullary tubuli. And yet the basic question of the mind’s action remained unanswered: Whether or no it constringes [sic] the Nerve, and by that means propels the nervous Juice more swiftly? Certainly there seems to be no other Way, by which that Juice can be propelled, than by Pressure at the Origin of the Nerves. But in whatever Way it acts, whether by propelling the Juice, or by dilating the Nerve, and deriving the Juice; the Difficulty in determining its immediate mechanical Action will always remain, that is, it will always remain to be accounted for, in what manner the Mind can act upon elastic Bodies which repel each other, so as to force them into the Nerves.92 Neither Boerhaave nor anyone else knew exactly how the mind could actually operate the spirit in a nerve, nor should this “be reasonably expected to be accounted for.”93 Indeed this was one of the main reasons why, as we have pointed out, “physic” was just “physic” and totally apart from “psychic” to Boerhaave, and also the reason why the celebrated Dutch professor made sure his students and readers understood certain things right from the beginning. The last two of ten main precepts, in particular, should be kept always present to avoid errors in medical practice: That, (9.) we cannot understand or explain the Manner in which the Body and Mind reciprocally act upon each other from any consideration of their Nature separate; we can (10.) remark by Observation their Effects upon each other, without explaining them; and when any Difficulty or Appearance has been traced so far, that it only remains to explain the manner of their reciprocal Action, we are to suppose such account Satisfactory, both because it may be sufficient for all the Purposes of the Physician, and as it is impossible to search any further.94 As the foregoing sections show, the animal spirit theory was for Boerhaave and his school much more than a simplistic, ingenuous belief. On the contrary, it was a hard-to-learn, advanced nerve and muscle physiology i.e., science on a difficult subject at its ultimate frontier so far, in a century drenched in optimism and confidence in the boundless power of human reason. Very much like our own. But science is always also a permanent intellectual battle requiring special skills, and, we shall see next, even the most respected of professors had to be on guard against real or perceived threats to his thinking. Page 25 of 39

Animal Spirit in Action Boerhaave Defending his Turf It is intriguing that Boerhaave did not always reflect the thoughts of his predecessors and contemporaries as accurately as he undoubtedly could. In some instances, mistakes seem to have been made unintentionally. But in others, especially when certain scientific ideas clashed with his own, questions can be raised about how he, one of the most knowledgeable and meticulous men of this era, could misrepresent certain experimental findings and ideas that should have been very well known to him. Of course, scholars shall never be able to reconstruct exactly what was going through his mind in such instances, but it must nevertheless be pointed out that some of his statements about what past or contemporary colleagues had to say about the nerve spirit were plainly wrong, whereas other rivals were denigrated and quickly dismissed. (p.169) Take, for example, Boerhaave’s comments about the suggestion introduced by Isaac Newton, and then afterwards developed by David Hartley, that nerve fibers transmit sensations to the mind and motor excitation to the muscles via vibrations.95 As pointed out in the preceding chapter, Boerhaave wrote without identifying the source that there is “no Face of Truth in that Opinion, which asserts the Nerves to perform all their actions by Vibrations, like those which arise from striking a tense Chord or Thread: since this is repugnant to the Nature of the soft, pulpy and flaccid Nerves which have so many Inflections and Incurvations.”96 He then goes on to clarify in an accompanying note that, Thus, say they, a Motion may be communicated from the Brain to any particular Part instantaneously, in the same manner as a Vibration is propagated from one Part of the tense Chord to the other without any sensible Interval of Time…but these Gentlemen [again, no names are given] do not consider the Impossibility of such Oscillations in the Nerves, which without their integuments are nothing more than a soft Medulla, so yielding, than an Ounce Weight will express all the pulpy Substance which the optic Nerve received from the Brain; but for a Body to be soft and flaccid like a Pulp, and to perform Vibrations like a tense Cord at the same time, is quite opposite to the Nature of things, and are Conditions that were never observed in any one Body.97

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Animal Spirit in Action In due fairness one must recall here that Newton and Hartley wrote of vibrations in a “medium” or in infinitesimally small “particles” within the nerve fibers, never referring to the fibers themselves as tense cords like those of a musical instrument. Moreover, Hartley, writing years after Boerhaave’s death, would specifically reject this last proposal as “highly absurd.”98 In addition, it cannot be overlooked here that Boerhaave was a leading authority on Newtonian theories, and one who incorporated many of the great physicist’s ideas into his own science. Hence the erudite Dutch professor, of all people, should have understood that Newton, with whose name the vibrational idea was most associated, never envisioned harpsichord- or bowstring-like nerves, though others may have misinterpreted the point. In another note discussing common arguments against a role for animal spirit in nerve function, Boerhaave refers to the famous experimental results obtained by his fellow countryman Jan Swammerdam and the Dane Niels Steno, who both demonstrated the weaknesses of the theory.99 Further, he mentions how snakes still slither after removal of the heart, that frogs swim after heart and lung ablations, and that eels continue to move after being cut into pieces, so their hypothetical hydraulic systems in charge of moving muscles were necessarily destroyed. Yet, in his words: all these are in Reality no objections to the Existence of a nervous Fluid; for the first two Experiments make nothing against us, and the rest only shew [sic] that the Fabric of the Nerves in cold amphibious animals is different from that of the Nerves in Quadrupeds and hot Animals; so that no Argument of Force can be thence drawn to make any Conclusion with regard to the human Body.100 This hasty and baseless spurning of actual facts and experimental observations is atypical in Boerhaavian writings, which is precisely why one cannot help but being left wondering about its motivations. Elsewhere, brief critical discussions of hypotheses put forward by preceding authorities—Galen, Descartes, Bernoulli, Willis, Borelli, Bellini—all unfitting in one way or the other for the animal spirit champion in Leiden, lead also to their prompt dismissal because those suppositions are all repugnant to Sense, the Fabric of the Organs, the Matter, Mixture and Proportion of the Humours, with the Continuance and Number of the Appearances observable in this Action. Nor have we the least Occasion to call in their Assistance.101

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Animal Spirit in Action Still, in other instances Boerhaave chose not to debate ideas that were against or deviated from the consistency of his impressive physiological integration, or dispute findings that he clearly perceived might be construed as challenging to his teachings. Instead, he appears to have intentionally misrepresented those very findings, and his defense of the animal spirit theory provides a good example of that kind of maneuvering. Thus, in a long section describing experimental lesions at several levels of the neuromuscular system and the interpretations of the corresponding results,102 he portrays Francis Glisson as supporting a conclusion that is the exact opposite of the one obtained by the English physiologist. Boerhaave reports that Glisson carried out an experiment that seemed to demonstrate “that the Muscles increase their Bulk at the time of Contraction,” and therefore, continues the Dutchman, “we may conclude for certain, that there must be an Accession of some Fluid, which enters and tumifies the Muscle with a moving Force.”103 Yet the fact of the matter is that Glisson, apparently after a demonstration presented a few years earlier at the Royal Society by Jonathan Goddard,104 wrote that “it is clear that the muscles when taut or contracted, are not at that time inflated or swollen, but are on the contrary unswollen and actually diminished.”105 Clearly Boerhaave did not think too highly of the intellectual abilities of some of his predecessors, saving his accolades for his beloved Hippocrates, the immortal Thomas Sydenham, and some select others, including Malpighi and van Leeuwenhoek, who did not try to come forth with general theories based on limited sensory experiences. In this critical distinction, however, he comes off as less than fair in more than a few instances, leaving knowledgeable readers scratching their heads. What is also noteworthy here is how far he was willing to go beyond (or around) the verifiable (p.170) facts at hand with his occasionally revisionist history and theorizing. Boerhaave’s account of the animal spirit theory may have been dressed in the finest clothes of the day, but underneath the finery there is still much that derives from the ancients, and also much that is based on reasoning well beyond what is obtainable through sensory impressions—that is, the speculative, “dubious,” and “uncertain” theorizing that Boerhaave routinely dismissed as “repugnant” and “corrupt” in others. In retrospect, even though he never reasoned about first causes, his cause-and-effect reasoning from some basic experimental observations was hardly restrained, and his speculations about the invisible animal spirit and secondary causes would not withstand the test of time.

Supporters and Dissenters

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Animal Spirit in Action Just as Boerhaave disagreed with many of his predecessors on a number of issues, the mechanistic position he championed was fiercely opposed by many of his cotemporaries. This should come as no surprise, given the wide range of views in the bustling early 18th century that we described at the start of this chapter. Although going into a detailed analysis of what many philosophers and scientists at that time thought about Boerhaave’s positions regarding the soul and animal spirit would be well beyond the scope of this book, some examples are in order. Thus, for example, in Britain, Thomas Morgan (d. 1743) regretted that

so great a Man as Professor Boerhaave lately attempted to support the Bellinian Hypothesis of muscular Motion,106 without answering any of the Objections, which had been brought by me and others against it.…In the fourth Edition of his Institutiones medicae, which I have now by me, and which was published in the Year 1727, he takes a vast deal of Pains to support the Bellinian Doctrine of muscular Motion, by the Influx of animal spirits from the Nerves; but to no other Purpose, that I can see, but to overthrow his own Hypothesis, and prove

Figure 10.8: Alexander Monro Primus (1697–1767), a Scottish physician who for a short while was a student under Boerhaave, eventually becoming a leader in the reputed school of medicine at the University of Edinburgh. Monro is counted among those who defended the teachings of their dear professor and friend at Leiden. (Line engraving by P. Thomson, 1793, after an original portrait by A. Ramsay, 1749; Wellcome Library, London, cat. V0004067)

himself mistaken.…But that the nervous Fibrillae are vascular, and that they convey a Fluid to the Nerves, which is the Cause of muscular Motion, is what I cannot conceive or believe.107

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Animal Spirit in Action The Scottish professor Alexander Monro Primus (1697–1767; Fig. 10.8), a former student and then junior friend of Boerhaave in Leiden before becoming himself a leader at the University of Edinburgh Medical School, came to his esteemed professor’s defense. In his treatise on the anatomy of the nerves, he spent over 20 pages and 30 paragraphs on an exhaustive examination of all the pros and cons of the nerve-spirit hypothesis, as compared with the vibration theory of nerve function. His allegedly sober analysis came out as very much biased in favor of the former.108 The whole subject, however, was not free of terminological and conceptual ambiguity and confusion. In a “rational” consideration of the matter by another author, who was also a reader of Boerhaave’s, it is held that the “animal spirits,” as they were generally understood, “have no foundation in any Phaenomenon that we know in nature…[and yet]…they must exist.”109 This revelation derives from an everyday observation: The Animal spirits are said to be good, when a person is lively, chearful [sic], and capable of all Animal actions, in such a perfection as our nature will allow. But this is saying no more, than that such a one enjoys a good state of health, whence ariseth that lively disposition. What is therefore meant by Animal spirits, is not so much a production of the Animal substances, as the pure effect or result of a Mens sana in corpore sano.110 This conception, one not far from our own current colloquial reference to a good mood as found in phrases such as “lift up your spirits,” was evidently too distant from the sanctioned theory then taught in medical schools throughout Europe. Equally misplaced was the location finally assigned to the animal spirit by that same author as a result of his ensuing long “rational” consideration, and clearly identified in the (p.171)

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Animal Spirit in Action proposition summarily stated at the beginning of the book: “That the Animal spirits so called, are not contained in the Nerves: But what can rationally be meant by Animal spirits, must be spirits existing in the blood only.”111

Other contemporaries attempted similarly unconvincing explanations. One of them was Emanuel Swedenborg (1688–1772; Fig. 10.9), a brilliant part-scientist, part-mystic Swede of many talents.112 Despite being an avid reader of Boerhaave, his general stance was opposite to that of the Dutch master: whereas, as discussed above, Boerhaave tried as much as he could to keep the study of the body strictly apart from Figure 10.9: Emanuel Swedenborg anything concerned with the (1688–1772), a Swedish scientist turned soul and mind, Swedenborg’s mystic via philosophy, guessed that a main interest was to analyze the “most pure fluid” in the nerve fibers (i.e., relationship between the animal spirit) is the medium of material and the spiritual communication between the soul and the spheres in humans and the body. (Engraved portrait on frontispiece universe at large. No doubt the of Opera Philosophica et Mineralea, tome most significant meeting place 3; Wellcome Library, London, cat. of both realms was the brain, M0006410) and therefore Swedenborg studied it in detail, trying to identify the specific regions of this organ associated with the higher faculties of mind. Following this approach, he realized the major importance of the up-to-then largely neglected cerebral cortex, and succeeded in localizing specific functions in different areas (e.g., voluntary motor functions in the opposite Rolandic region, thinking and planning in the front part of the brain). Consistent with his overall neurophysiological scheme, Swedenborg held the nerve spirit in the highest regard:

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Animal Spirit in Action From the anatomy of the animal body we clearly perceive, that a certain most pure fluid glances through the subtlest fibres, remote from even the acutest sense…. This fluid is in the third degree above the blood, which it enters as the first, supreme, inmost, remotest and most perfect substance and force of its body, as the sole and proper animal force, and as the determining principle of all things. Wherefore, if the soul of the body is to be the subject of inquiry, and the communication between the soul and the body is to be investigated, we must first examine this fluid.113 As it happened, however, Swedenborg’s theories and findings fell on deaf ears, in part because he did not teach at a university nor publish his observations in widely disseminated books of medicine. Regrettably, some of his key writings on neurological subjects were not even published until the 1880s, by which time the concept of cortical localization of function had strong support from others.114 Still, as by now the reader has surely noted, Swedenborg’s comparatively late views on the nervous spirit only harked back again to the fatigued old notions passed on by the ancient Greeks and pulled along throughout the Middle Ages. It had become pretty obvious that the theory of nerve function was in urgent need of some fresh air. Then, at around the middle of the century, at least a few professors started to presage a different way of looking at nerve function—that is, with a frame of mind that would take research beyond the views expressed by Boerhaave and mostly everyone else.

New Horizons One representative instance of this awareness is a well-informed British professor of anatomy and physiology named Charles Nicholas Jenty, active in the first half of the 18th century and author of a three-volume series of lectures that came out in 1757 and went through several editions. In a balanced review of neuromuscular phenomena that clearly follows what Alexander Monro had previously done, Jenty went a step further than the Scottish professor. Critical of the hypothesis of nerve fiber vibrations, and abstaining almost completely from using terms like “spirit” and its derivatives, the author nevertheless still adheres to the (p.172) paradigm of a nervous fluid. But whereas Monro virtually always referred to this as a “liquor,” Jenty shows a preference for the Newtonian word “aether.” And then we are presented with a novel analogy that is worth quoting here at some length, since it reflects a notable change in thinking that was beginning to occur: The surprising Discoveries which have been made of late Years, by a Variety of Experiments upon Electricity, do in some Measure give us an Idea of the great Subtility and Velocity of the nervous Fluid. I have been informed…that the Swiftness of the electrical Effluvia is prodigious…and perhaps this may be very similar to the Motion and Action of the nervous Aether. Page 32 of 39

Animal Spirit in Action Thus much being premised, and it being taken for granted, that we have an aethereal Medium in the Brain, the Spinal Marrow, and all the Capillamenta of the Nerves, ever ready to be conveyed into the muscular Fibres, by the Power of the Will, and which Medium consisting of the most refined Matter in Nature; it follows, that the Motion of this nervous Aether may be as quick as Lightning, and also its attractive Power must be exceeding strong, by Virtue of its vast Degree of Subtility; as is evident from what Sir Isaac Newton has calculated concerning the Rays of Light.115 Having commented earlier on the attractive power of the electric matter (static electricity) that is “excited” by rubbing certain nonmetallic materials together, Jenty states: I think we have great Reason to conclude, that muscular Motion does proceed from the influence which the nervous Aether has upon the component Particles of the muscular Fibres themselves, by instantly increasing their attractive Virtue towards each, so as to make them run closer together, or, as it were, up into Heaps, as long as such an additional attractive Medium is in the Fibres. A Newtonian aether, rather than animal spirit, causing mutual approaching of the particles constituting muscle fibers, as Hartley had supposed, yet not through mere oscillatory vibrations but by flowing instantaneously along nerves, rather like the electrical fluid? This curious mix of vibrationism and the classic stream-like model of nerve messaging, with a twist to the exciting new physics, is just a transitional foretaste to a subject that we will have much to say about in the final three chapters of this book. But first we must take a brief look at a longstanding parallel development in biological thought, by which nerveindependent—and therefore unrelated to animal spirit—apparently autonomous actions of muscles and other organs were explained throughout the centuries. Notes:

(1) See Chapters 6 to 9. (2) Descartes, 1649, Fifth Article; see also Chapter 6. (3) Stahl, 1708. (4) King, 1964. (5) Rather and Frerichs, 1968, p. 36, XXX; see also Stahl GE, Leibniz GW, 2004, p. 101, XXXI. Note: Doubt XXX in the English translation by Rather and Frerichs corresponds to Doubt XXXI in the French version, because the former includes the two parts of Doubt XXII as items a and b, thus numbering only 30 doubts.

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Animal Spirit in Action (6) Rather and Frerichs, 1970, p. 61. (7) Stahl GE, Leibniz GW, 2004, p. 143, Réplique XXXI (here translated by the present author). For a review of Leibniz’s conceptions about medical matters see Grmek, 1990. Unfortunately this last paper does not cover ideas on the nervous system or the subject of animal spirit. (8) See Chapter 9. (9) Stahl, 1720. (10) See Greek and Roman atomism, Chapter 1. (11) Hoffmann, 1746/1754, p. 438, §39 (quoted in King, 1964). (12) Hoffmann, 1695, Chapter 3, §24–25 (King, p. 13). (13) Ibid., §18 (ibid., p. 12). (14) Ibid., Chapter 5, §20–21 (ibid., p. 20). (15) Ibid. (ibid.). (16) Ibid., §47 (ibid., p. 22). (17) Ibid., §49–50 (ibid., p. 23). (18) Ibid., §53 (ibid., p. 23). (19) Ibid., Chapter 6, §20 (ibid., p. 25). (20) Ibid., §3 (ibid., p. 24). Square brackets as in the original. (21) Ibid., §9 (ibid.) For precedents about the weight-raising power of inflated bladders, see Chapter 8. (22) For a contemporary biography of this important and unusual man see Burton, 1746. An authoritative modern study can be found in Lindeboom, 1968, and in compact form in Lindeboom, 1975. For more recent essays see Cook, 2000, and Knoeff, 2002. (23) See Chapter 17 in Lindeboom, 1968; Ashworth Underwood, 1977; Hull, 1997. The views of several former students of Boerhaave will be reviewed in this and the next chapters. (24) Spinoza, 1677, Part II, Prop. 13 (White and Stirling, 1990, pp. 611–614).

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Animal Spirit in Action (25) To what extent he succeeded in this purpose is controversial. For contrasting opinions about how Boerhaave’s religious views may have oriented his scientific thought see Cook, 2000, and Knoeff, 2002. (26) Boerhaave, 1742–1746, vol. 1, §21, n. 2, p. 53; see also §27, pp. 65–70. This edition is the standard English translation of Boerhaave’s Institutiones medicae, after the original Latin version edited by Albrecht von Haller, to which all verbatim quotations of this work are here referred. (27) Skinner, 1961, p. 325. (28) The sole expression selected to show the use of the word physician for a medical doctor, in a digital version of a well-known dictionary—“physician of the soul”—would have sounded contradictory or even blasphemous in the 17th and early 18th centuries. Certainly Boerhaave would have frowned upon hearing it. (29) In practice it is in chemistry where the key to most of natural philosophy, in particular as regards medical matters, is to be found; see Boerhaave, 1735, Part II, pp. 50ff. (30) Boerhaave, 1742–1746, vol. 1, §29, n. 1, p. 74. The milestone contributions to this story by Albrecht von Haller will be reviewed in Chapter 12. (31) Boerhaave, 1735, Part II, pp. 36ff. (32) Ibid., p. 47. Boerhaave’s conceptions about spirits can also be found in his 1730–1735 treatise on nervous diseases (Boerhaave, 1959). For a condensed presentation see Koehler, 2007. (33) “Juice” is in fact the term used interchangeably with “Spirit” in the standard English translation. The expressions found in the original Latin version, however, are Spiritus cerebri and Spiritus nervorum; see for example Boerhaave, 1752, heading in pp. 128–130, and p. 134, §291. (34) Croone, 1664, Section 13, p. 7 (Croone, 2000, p. 72–73); see also Chapter 6. (35) Boerhaave, 1742–1746, vol. 2, §277, pp. 294–295. (36) Ibid., §275, p. 290, and §277, n. 4, p. 297. (37) Ibid., §275, n. 2; p. 290. (38) Vesalius, 1553, Book VII, 12; see Chapter 5. (39) Galen, Usefulness of the Parts, Book IX, 4 (May 1968, vol. 1, pp. 430–434); see also Chapter 2.

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Animal Spirit in Action (40) Boerhaave was an expert on Vesalius’ work, having published a new edition of the great Fabrica in collaboration with his student Bernhard Siegfried Albinus (Boerhaave and Albinus, 1725). (41) Boerhaave, 1742–1746, vol. 2, §291, pp. 325–326. (42) Ibid., §289, pp. 318–323, and notes. Quotations in this paragraph are all referred to these pages. (43) Ibid., §290, p. 324. (44) Ibid., §237, p. 202, and §235, n. 9, p. 197; see also §269–271, pp. 271–278; and §277, n. 4, p. 297. In the original Latin version Boerhaave used the term Medulla cerebri as opposed to Cortex cerebri (e.g., Boerhaave, 1752, p. 112), obviously in the general sense of the noun as derived from medius, “what is in the middle,” as for example did also Vesalius referring to the inner part of bones (see also Skinner, 1961, pp. 268–269). Thus Boerhaave’s “medulla of the brain” is not to be confused with the term Medulla oblongata that he uses for most of the brain stem (see immediately below), nor with its continuation the Medulla spinalis or “spinal Marrow”; for details see Boerhaave, 1742–1746, vol. 2, §237, nn. 4 and 5, pp. 203–204. (45) Ibid., §274, p. 285. (46) Ibid., §284, n. 5, p. 310. (47) Ibid., §286, n. 1, p. 313. (48) See Clarke, 1978. (49) Boerhaave, 1742–1746, vol. 2, §292, pp. 326–328. (50) Ibid., n. 1, p. 328. Apparently this last term refers to sweat, since blood descending through the subclavian, axillary, and brachial arteries down to the hands is the cause of the “sensible Perspiration observable there…whence the Heat and Sweating of the Palms;” ibid., §305 with notes, pp. 353–354. See also Boerhaave, 1742–1746, vol. 3, §424, n. 4, pp. 302–303. (51) Ibid., vol. 2, §284, p. 307. (52) Ibid., §287, pp. 314–315. (53) Ibid., vol. 2, §288, pp. 315. (54) Ibid., vol. 5, §768, pp. 438–439.

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Animal Spirit in Action (55) Ibid., vol. 5, §783, p. 469. There is a parallel here with ancient Greek views about health problems caused by interference with the flow of pneuma in the body (see Chapter 1, esp. note 39). (56) Ibid., vol. 6, §1180, item 9 with n. 7, pp. 377, 379. Please note that, in turn, the “Passions of the Mind are altogether febrile Disorders of the Spirits”; ibid., vol. 5, §783, n. 3, p. 470. For more on passions according to Boerhaave see Cook, 2000. (57) Ibid., vol. 6, §1180, n. 7, p. 379. (58) Ibid., §1181, p. 379. (59) Ibid., §1182, p. 380. (60) Ibid., §1180, n. 8, p. 379. (61) Ibid., vol. 4, §569, n. 1, p. 234; see also vol. 2, §288, n. 1, p. 317. (62) Hartley, 1749, Prop. 4, pp. 11–12; see also Newton, 1718, Query 21, p. 326; theory discussed in Chapter 9. (63) Boerhaave, 1742–1746, vol. 4, ibid., §516 and n. 3, pp. 74 and 76. (64) Ibid., §542 and n. 1, pp. 142–143. (65) Ibid. (66) Ibid., §561, pp. 207–210. (67) Ibid., §495, n. 1, pp. 32–33. (68) Ibid., §566 and n. 1, p. 226–228. (69) See Koehler, 2007, p. 220. (70) Boerhaave, 1742–1746, vol. 4, §570 and n. 4, pp. 234–236. (71) Ibid., §491, n. 1, p. 26. (72) Ibid., §574, n. 2, p. 247. (73) Ibid., §568 and n. 3, p. 230. (74) Ibid., §568, n. 3, p. 231–232. (75) Ibid., §572, p. 242. (76) Ibid., §573, p. 245.

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Animal Spirit in Action (77) Ibid., §574, p. 246. (78) Ibid., n. 2, p. 248. (79) Boerhaave, 1742–1746, vol. 3, §388–416, pp. 164–271. (80) Reportedly Bartolomeo Eustachius, Raymond Vieussens, and Marcello Malpighi; ibid., §395, n. 4, pp. 178–179. (81) Ibid., §395, p. 176. (82) Ibid., n. 6, p. 180. (83) Ibid., §401, items 13–14, p. 195. (84) Galen, De motu musculorum, I, 8 (Goss, 1968); Harvey and Glisson are both discussed also in Chapters 7, 8, and 11. (85) Boerhaave, 1742–1746, vol. 3, §401, n. 24, p. 215. (86) ibid., §402, item 7, p. 216. (87) Ibid., 217. (88) Ibid., §403, p. 222. (89) Ibid., §404, pp. 223–225. (90) Ibid., n. 1, p. 224. (91) Ibid., §407, n. 2, p. 230. (92) Ibid. (93) Ibid., §407, p. 229. (94) Ibid., vol. 1, §27, p. 66. Numbers within parentheses correspond to the precepts being considered. (95) See n. 62 above. (96) Boerhaave, 1742–1746, vol. 2, §285, p. 310. (97) Ibid., n. 1, p. 311. (98) Hartley, 1749, Prop. 4, pp. 11–12. (99) See Chapter 7. (100) Ibid., vol. 2, §285, n. 3, pp. 312–313. Page 38 of 39

Animal Spirit in Action (101) Boerhaave, 1742–1746, vol. 3, §408, pp. 231–235. (102) Boerhaave, 1742–1746, vol. 3, §401, pp. 191–216. (103) Ibid., n. 21, pp. 213–214. (104) See Birch, 1756, vol. 2, pp. 411–412. (105) Glisson, 1677, p. 167 (Fulton and Wilson, 1966, p. 219). See also Chapter 7. (106) The reference is to Lorenzo Bellini (1643–1704), an Italian iatromechanist follower of Giovanni Borelli, who developed an influential hydraulic kind of physiology based on fluid rather than solid mechanics. For a short biographical sketch see Brown, 2008. (107) Morgan, 1735, pp. 149–151. (108) Monro, 1741, §29–62, pp. 11–30. (109) Kinneir, 1739, p. 13. (110) Ibid., pp. 11–12. (111) Ibid., p. 5. (112) Swedenborg is not a popular figure among historians of the medical sciences. For compact reviews of his singular place in the history of neuroscience see Norrving and Sourander, 1989, and Finger, 2000, pp. 119–121. For an easily available full-scale biography see Benz, 1948/2002. His own representative works on medical subjects include Swedenborg, 1741, and 1882, 1887. (113) Swedenborg, 1741, §219, p. 211. (114) See Finger, 2000. (115) Jenty, 1757, vol. 1, Lecture 15, pp. 333–334.

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Non-Spiritual Physiology I:

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Non-Spiritual Physiology I: “Physic” Rather than “Psychic” Functions C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0011

Abstract and Keywords This chapter outlines the views about physical or natural responses from ancient Greek philosophers until the revolutionary medical theories that were introduced by Giorgio Baglivi and Francis Glisson. It studies Baglivi's claim that fibers composing the organs—particularly the muscles—are directly responsive to irritation. It shows that the Scientific Revolution that occurred during the Renaissance had deeply affected the understanding of living matter in a deep and very basic way: Organs were all composed of fibers, despite their differences in form and function. Gottfried Leibniz is credited as being the first one to have held this view. Keywords:   physical responses, medical theories, Giorgio Baglivi, Francis Glisson, fibers, irritation, Scientific Revolution, living matter, organs, Gottfried Leibniz

The motions and actions which physicians style natural, because they take place involuntarily…and they therefore do not depend on the brain, still do not occur entirely without causing sensation, but proclaim themselves subject to sense, inasmuch as they are aroused, called forth, and changed thereby. William Harvey, 1651, Anatomical Exercises on the Generation of Animals, Exercise 57 (Willis, 1990, p. 456). Page 1 of 22

Non-Spiritual Physiology I: Scientific theories gather support from concordance with observed facts, and from the “reasonableness” of their interpretation in terms of current knowledge. This happened also with the theory of animal spirit: it had a reasonable and respectable background in the framework of Greek medical doctrines, and it was fully compatible with the advanced automaton engineering of the 17th century. Yet there are always gaps in every theory and, as reviewed in the previous chapter, even the most eminent Boerhaave confessed ignorance about, for example, the key question of how the “celerity” of the animal spirit might be differentially regulated in contiguous nerves activating antagonist muscles. Since a vacuum in knowledge always stirs the emergence of alternative or complementary theories, the questions left unanswered by the extant ideas about animal spirit prompted the proposition of ad hoc hypotheses. In this chapter and the next we shall examine how certain apparently odd facts led to the parallel development of a rather unorthodox conjecture, one that throughout the centuries would continue to creep its way along the sidelines of the main theory. Such a supposition attempted to account for the immediate responsive behavior of living matter—a phenomenon observed since antiquity in some definite cases—through conceiving the existence of a special property essentially independent of animal spirit. We will find here again, under a different light, names that were introduced already in previous chapters, and in addition we will meet new players in the long-lasting endeavor of finding out how living organisms are capable of dynamically relating to their environment. The reader is kindly asked to look on the chapters indicated in the notes for general information about authors already mentioned in this book.

Odd Facts As we have seen, up to the European Renaissance there was overwhelming consensus if not general agreement that—if we are permitted to abuse the words just for the sake of stressing the point—every animal is animated by an anima, where animation is to be understood as the capacity of moving coordinately, either as a voluntary act or in response to external factors. Then, in the 1600s, René Descartes gave voice to the feeling of the still few but increasingly numerous dissenters, who found it more reasonable to conclude that the anima has little to do with managing the body it inhabits, for its main occupation is rather to think, a faculty existing only in humans among the mortal terrestrial beings. According to this view, the so-called “animals” should be regarded to a large extent more like automatons,1 and perhaps some of these heretics would have endorsed a proposal for calling beasts with a neologism such as “machinals,” more adequate to point out their true ontological soulless status.

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Non-Spiritual Physiology I: But even hard-core Cartesians admitted that, in order to function as a coordinated unit and relate effectively to the environment, a fast communication system is necessary among the multiple parts of an animal body. This system, almost everyone agreed, must be composed of nerves connected to the central nervous organs located within the head and the backbone in the vertebrates, or in analogous regions of the body in other kinds of animals. The actual seat of the soul was thought to be the “common sensory or sensorium,” (p.174) most likely found in the medullary region below the brain’s cortex, where all sensations are received and from where all the appropriate motor responses are dispatched. Animal spirit constitutes the medium, contained within the nerve fibers, through which all those input and output signals are conveyed. In fact, only Georg Ernst Stahl2 and his followers sustained that the anima itself could act directly at every point in the body, as it is locally required at every moment. Nevertheless, a difficulty with such standard model, for which lots of supplementary explanation was demanded, arose with physiological processes that occur automatically without necessarily being consciously perceived. These were assigned to several different categories, apart from the beating of the heart, which was in a class of its own as the source of all other bodily activities. Take breathing or digestion, for example. Each of these functions goes on normally, even during sleep, without the awareness of the individual in whom they take place. They were considered as routine, housekeeping vital jobs dependent upon the cerebellum, rather than psychic functions that necessarily involve the will and therefore the brain itself. Yet even in these cases the soul can take notice of their occurrence, if she so wishes, just by paying close attention to the body. Thus we can all know exactly when we inhale and when we exhale. Moreover, within limits, it is even possible to command breathing at will. Digestion is completely automatic and beyond direct willed control for us, but we can still realize it occurs after meals because it is accompanied by a number of vigorous though usually low-level internal sounds. Even if we are commonly unable to perceive these in our own bodies, we can hear the rumbling of the entrails in any dinner companion who allows us to apply an ear to his or her belly. Needless to say, crosstalk between the cerebellum and the brain can keep the soul well abreast of these basic vital operations of the body, should this be warranted. Thanks to such communications, for example, deliberate motions are executed if something threatens to block respiration, or if bodily activity is impaired as a consequence of an uneasy digestion.

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Non-Spiritual Physiology I: Far less clear was the situation of an organ that seems to react largely by itself, one without any noticeable message to the soul, and without the possibility of being under even minimal control of the will. This is the case with the exceedingly discreet gallbladder, the small muscular pouch below the liver where bile, one of the four classic humors, is temporarily stored before use. At the appropriate time after food is ingested, the gallbladder contracts and releases a fair quantity of its contents into the duodenum, the initial portion of small intestine following the stomach. Once there, the bile was imagined as greatly helping for the cleanup of many unnecessary residues that come with the food. Hence, it was viewed as critical for a good maintenance of the alimentary tract, and therefore as a main focus of medical attention since antiquity. Not surprisingly, the container storing this fluid, the gallbladder, remained an equally ancient source of problematic questions because, among other peculiar features, it is scarcely supplied with nerves. So, how does the soul know exactly when to order the gallbladder to eject the bile on due time for the latter to perform its supposedly cleansing action? Is the distant “common sensory” within the head perhaps capable of issuing certain commands spontaneously and on a timely basis without the intervention of some sort of remote detection? And if so, through what channel other than nerves is that motor command quickly conveyed? Or could it rather be that the gallbladder itself determines when to execute its own contraction? In this seemingly autonomous property, the little pear-shaped sac stands apart from all other hollow organs. Although the stomach operates usually by itself, the fact that vomiting can be induced voluntarily or by other psychological factors (e.g., seeing internal organs in a surgical operation, or a partly decomposed body) indicates at least some degree of psychic subordination. Additionally, the intestines and the urinary bladder both report to the soul (mind) about their state of distention, and in healthy adults they obey its willful orders concerning evacuation. Even the uterus sends urgent signals as soon as its activity is initiated in childbirth labor. The gallbladder is different. In the following paragraphs we shall briefly review the legacy of ancient opinions about the problem posed by the gallbladder and similar “soulindependent” body parts, as an introduction to the emergence of new ideas on the topic during the 17th century. These in turn would evolve into certain outrageous propositions that appeared in the Siècle de Lumières, which we shall see in Chapter 12.

Distinguishing “Animal” from “Natural”

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Non-Spiritual Physiology I: The complementary capacities of sensing something and executing an appropriate motion (i.e., the two basic faculties of the nervous system) were known from ancient times to exist even in inorganic matter. As mentioned at the beginning of our journey, Thales of Miletus, hailed as the first great Western philosopher, reportedly attributed a soul to the lodestone precisely because it shows such properties.3 Again, growing plants obviously also have intrinsic abilities to distinguish up from down when they elongate stems and roots, as well as to orient themselves in relation to the sunlight. Hence Plato acknowledged they partake of that “third type of soul,” which in humans is “situated between the midriff and the navel.”4 Such a soul, however, is totally devoid of opinion, reasoning or understanding, though it does share in sensation, pleasant and painful, and desires.…Hence it [i.e., a plant] is alive, to be sure, and unmistakably a living thing, but it stays put, standing, fixed and rooted, since it lacks self-motion.5 Aristotle also granted the simplest kind of soul to plants, one that only permits nutrition, growth, and reproduction, in contrast to that of animals, which in addition is capable of sensation and in many cases of promoting self-movement.6 (p.175) Nevertheless thereafter, starting with the Stoic philosophers in the Hellenistic period that followed Aristotle’s death, vegetation was deprived of even that lesser or minimal soul. They recognized that it is nature (physis) that first organizes the bodies of living beings: “in their view [of the Stoics] it is Nature which puts together the bodies both of plants and animals; and this she does by virtue of certain faculties which she possesses—these being, on the one hand, attractive and assimilative of what is appropriate, and, on the other, expulsive of what is foreign.”7 This Stoic lead was then picked up in the second century CE by Galen, who produced a three-book treatise on the subject of those “natural” (i.e., physic, as opposed to “animal” or psychic) faculties. He started the first of these books with the following lines: Since feeling and voluntary motion are peculiar to animals, whilst growth and nutrition are common to plants as well, we may look on the former as effects of the soul and the latter as effects of the nature.…accordingly we employ those terms which the bulk of people are accustomed to use, and we say that animals are governed at once by their soul and by their nature, and plants by their nature alone, and that growth and nutrition are the effects of nature, not of soul.8 Thus life is possible without a soul, even if simple and quite limited. Yet, according to Galen, this means that there could be many body functions in higher animals and humans that might occur via the exercise of the natural faculties alone, independently from the soul. Thus, for example, Page 5 of 22

Non-Spiritual Physiology I: when the stomach is sufficiently filled with the food and has absorbed and stored away the most useful part of it in its own coats, it then rejects the rest like an alien burden. The same happens to the bladders [urinary and biliary], when the matter attracted into them begins to give trouble either because it distends them through its quantity or irritates them by its quality.9 Such trouble is accompanied in most of these organs by discomfort or even pain. The exception is the bladder alongside the liver, whence it is clear that it possesses fewer nerves than do the other organs. Here too, however, at least the physiologist must discover an analogy. For since it was shown that the gallbladder attracts its own special juice, so as to be often found full, and that it discharges it soon after, this desire must be either due to the fact that it is burdened by the quantity or that the bile has changed its quality to pungent and acrid.10 The mechanics involved in attracting, retaining, and discharging contents in such organs that behave according to nature, rather than according to a soul, are carried out by three sets of properly oriented fibers embedded in their walls, each set performing a specific task: There was good reason for it [the inner tunic of each bladder] to have the movement performed by the straight fibers in order to attract, that performed by the transverse fibers in order to expel, and that performed by the oblique fibers in order to clasp its contents on all sides and retain them. If only the transverse fibers are tensed, the breadth becomes less; if the straight fibers act alone, the length is decreased; but if straight, transverse, and oblique fibers all draw together at once, the whole part is contracted, and when they all become longer, it expands.11 Now, we are usually unaware of these operations because “all these parts [kidneys, spleen, liver, and gallbladder] receive exceedingly small nerves which are to be seen on their outer tunics, because Nature has granted to each one of them only as much sensation as is necessary to distinguish them from plants and make them animal parts.”12 And the reason for making these parts “animal” (i.e., with at least a sensory relationship to the psyche or anima) was just a safety measure for preventing dangerous and extreme circumstances; in other words, Galen goes on, “conferring perception of what will cause pain […for…] If they were completely without sensation, they would all, I think, be easily ulcerated, eaten away, and putrefied by the daily supply of residues flowing into them.”13

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Non-Spiritual Physiology I: Therefore both the functions of the natural faculties as well as their instruments, namely fibers, were quite clear to Galen. Yet, he confesses, the term “faculty” should be taken as just a provisional handy name awaiting further investigation. As he put it: “so long as we are ignorant of the true essence of the cause which is operating, we call it a faculty [dynamis or moving force].”14 To Galen this power of the vegetative organs (organa physica) is something analogous to that by which the magnetic stone can attract iron.15 In other words, it is a “natural” (physic) property, not an “animal” (psychic) virtue as Thales had supposed. We will see below how the self-discharging faculty of the humble gallbladder sparked new thinking in the late 17th century. But before going into the Early Modern era we must mention another class of organs, much closer to our main interest here, that according to Galen also exhibit a natural faculty despite being perhaps the most “animal” of all: muscles. In his first book dedicated to these organs Galen states: When a dead [i.e., freshly excised] muscle, which has none of the influence of the brain [psychikos], has been cut across entirely, you see it retract toward the ends. This would seem, not illogically, to be the work of the constitution of the muscular substance. If the substance of the muscle is intended by nature [physis] to retract itself, what need is there of the psychic power to move it (p.176) unless the power from the brain is useful for making the muscles to give way to each other’s motions?16 Thus the possibility that skeletal muscles, the organs in charge of moving our limbs and hands, and therefore of serving as the ultimate instruments for the expression of our own free will, might act in principle by themselves independently from the direct control of the soul, was already formulated in antiquity. Since, as we know, little was added to or changed in Galenic physiology during the Middle Ages, this line of our story would be continued in the Renaissance.

Distinguishing Sensation from Perception The doctrine of the natural faculties was admitted in general by Andreas Vesalius,17 the more influential critic of Galenic anatomy, who agreed that the internal hollow organs have inherent capacities for attracting, retaining, and expelling their contents as required to fulfill the various demands in the many parts of the whole body. He pointed out, however, that many organs also possess another ability to attract their own nourishment from the blood in order to stay in optimal condition. In contrast to the common faculties, which are carried out by the three classic types of fibers, this local attraction is “produced solely by a force innate in those parts without any assistance from fibers.”18 Here we have a further instance, 14 centuries after Galen, of a vital necessity in the satisfaction of which the participation of the soul was not deemed essential. Page 7 of 22

Non-Spiritual Physiology I: William Harvey,19 a prominent alumnus of the Vesalian school, was even uneasier with traditional medical theory, in particular as regards the actual seat of life and soul. In his treatise on animal generation Harvey claims, contrary to general belief, “that sensation and motion belong to the foetus before the brain is formed, for the foetus moves, contracting and unfolding itself, when there is nothing more than a little limpid water in the place of the brain.”20 No brain, no seat of the soul in Galen’s physiology. Consequently, Harvey reasoned, there must be at least a “natural” or physic (again, as opposed to “animal” or psychic) sense of touch: as there are some actions and motions the government or direction of which is not dependent on the brain, and which are therefore called natural, so also it is to be concluded that there is a certain sense or form of touch which is not referred to the common sensorium, nor in any way communicated to the brain […] Now such a sense do we observe in zoophytes or plant-animals, in sponges, the sensitive plant, &c. […] so also do certain actions take place in the embryo and even in ourselves without the agency of the brain, and a certain sensation takes place without consciousness.21 Thus, in Harvey’s view, the so-called “natural faculties” must be taken to include not only motions but feeling as well, a complementation that is fortunate because only through the coupling of both properties through “irritation” are we able to study living things: For that which is wholly without sense is not seen to be irritated by any means, neither can it be stimulated to motion or action of any kind. Nor have we any other means of distinguishing between an animate and sentient thing and one that is dead and senseless than the motion excited by some other irritating cause or thing, which as it instantly follows, so does it also argue sensation.22 Regarding the primary source of such faculties Harvey had no doubts. He argues convincingly—disagreeing here strongly with Aristotle, despite his generally Aristotelian views—that the blood is always first: “the privilege of priority [appearing first during embryonic development] belongs to the blood alone; the blood being that which is first seen of the newly engendered being…From this [among other reasons] it clearly appears that the blood is the generative part, the fountain of life, the first to live, the last to die, and the primary seat of the soul.”23

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Non-Spiritual Physiology I: What are then the roles of the central nervous system in Harvey’s conception? In brief, general control and coordination, for “it is one thing for a muscle to be contracted and moved [like in random spasms and convulsions], and another for it by regulated contractions and relaxations to perform any movement, such as progression or prehension.”24 The difference between the two kinds of movement depends on the brain, though the basic “natural motions,” we are told immediately after, “proceed from the power of the heart, and depend on it.” It would remain for scientists of future generations to discover how muscle power might work.

Irritability A younger philosophically minded physician in 17th-century Britain, Francis Glisson, found inspiration in Harvey’s new and strangely fresh ideas.25 We have noted in Chapter 8 that Glisson was among the first to question, based on experimental evidence, that muscles swell when they contract, as was maintained by most proponents of the animal spirit doctrine. Now we will briefly look into how he arrived at a complementary conclusion, according to which muscle contraction is to be viewed as an essentially self-contained phenomenon. In considering how it is that the gallbladder—once again—excretes bile at a certain moment and not at another during digestion, Glisson concluded in orthodox Galenic terms that this occurs because the relentless increase in the (p.177) content of the small vesicle eventually distends it beyond a given limit, at which point it becomes “irritated.” To quote: “if the parts thus irritated are hollow, membranous, and fibrous, their resistance must needs occur through contraction of all fibres, until their cavity is reduced to a smaller compass and some part at least of the humor contained therein is removed to the outside, all of which holds true in the gallbladder.”26 Reflecting upon this ability of some body parts to react directly to local stimulation, and under the influence of Harvey’s speculations on the immanency of life in all parts supplied with blood, Glisson arrived at a comprehensive hypothesis of responsiveness in matter at large.27 According to this view every substance exists at the same time in two senses: as a material presence and as a container of energy that is the fountain of all action. Life is the spontaneous release of such energy, and therefore it can be found in many natural forms, even in the inorganic world. In every case the internal energy is manifested when some kind of “motion” occurs, as the substance in question “perceives” anything that can satisfy a basic “appetite.”28

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Non-Spiritual Physiology I: Since the basic “appetite” is always permanent and energy is indwelling in matter, the key to eliciting “motion” must be “perception” (perceptio). It is mainly through “perception” that substances in the different kingdoms of nature are distinguishable from each other. Biological entities, given their constitution with various functional systems, can have up to three different modalities of “perception”: (1) “naturalis”—that is, a basic direct response of living matter to stimulation; (2) “sensitiva,” which involves the transmission of information through nerves to a brain that thus becomes aware of the occurrence of an external stimulus, and which therefore can include conscious sensation; and (3) “animalis,” in which the stimulus comes from the soul itself. According to this conception, virtually all parts in the animal body have some ability to sense a change in their own substance or immediate surroundings, and most of them also have the capacity of executing in return some action, with or without the necessary intervention of the nerves. In other words, they are “irritable.”29 Such automatism is categorically different from that proposed by Descartes and his followers as an explanation for the self-movement of living organisms.30 As an alternative to the sophisticated clockwork mechanism envisioned by the Cartesians, in which every part of the apparatus is driven by the immediately adjacent part, Glisson conceived of a machine in which minute springs or small levers (i.e., fibers, see below) possess the faculty of executing simple movements by themselves. And this was not just the product of pure imagination. Danish physiologist Niels Stensen (Nicolaus Steno in Latin works) had recently concluded that the “fibra motrix,” a definite structure that is in turn made up of tiny fibrils, “is the true organ of the movement of an animal.”31 This conviction was based upon a number of observations, among which it can be read that the constitutive fibers do not all shorten always at once in the heart and other muscles, but rather “individual fibers move separately at different times.”32 Nor was Glisson the only one thinking about possible answers to explain this curious phenomenon. At about the same time in Oxford, John Mayow supposed that single muscle fibrils would shorten by contortion, just like a fine musical string will twist and contract when it is exposed to a candle flame that heats it up without reaching the actual burning point.33 The source of such intense local heat within the muscles, according to Mayow, is the violent reaction generated when particles of “nitro-aërial [i.e., animal] spirit” released by the nerves enter into contact with the “saline-sulphurous particles” contained in the muscles themselves.

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Non-Spiritual Physiology I: Glisson’s concept was subtler than this, far less physical and in a sense more biological. He became convinced that living matter possesses a unique primitive capability, “irritability,” based on the general energetic properties of all matter.34 It is independent from and also antecedent to the soul, because it also dwells in inanimate substances. Years later, when he again wrote about gastrointestinal topics,35 irritability was already a major protagonist in his physiological scheme. Fibers in the animal body would respond to their being touched by foreign objects, or to exposure to other external or internal circumstances, because they are endowed with inherent natural perception: “You may say that the fibres are particles equipped with sensibility which can be excited by reason of their capacity of sensation [feeling].”36 Once a fiber detects a change of conditions affecting it, one of three possible reactions may occur. The simplest one is merely moving either towards or away from the cause of the change, depending upon the pleasant or unpleasant quality of the latter, and then returning to the initial state. No nerves are involved in this local transient response, so that neither the common sensorium in the brain nor the soul seated there becomes aware of the disturbance, everything occurring below the level of consciousness. Now, some fibers are connected to nerves at certain specialized places of the body, typically in the external sense organs but also in those in charge of reporting internal conditions. In these cases the brain is immediately informed of the local reaction, so the soul becomes updated about changes in the environment or in the body itself. This involvement, in turn, (p.178) may be followed by appropriate motor commands issued through the nerves to certain muscles, again depending upon the nature of the stimulus. The third possibility is that the soul takes the initiative and the brain “moves the fibre of the muscles in order to seek that which it desires.”37 The power of irritability requires the fibers to be “imbued with resident spirits [spiritibus insitis] and with those inflowing, vital spirits [influentibus, hisque vitalibus],” the latter being provided by the blood. But as a property basically independent from the soul, and therefore also from the nervous structures, irritability operates in muscles and other body fibers without the involvement of animal spirit. This does play its usual transmitting role in Glissonian physiology, but not in the primary mechanism of living matter as it responds directly to stimulation.

The Rise of the Solids

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Non-Spiritual Physiology I: A most interesting situation was now a part of the scene. Fibers, which for centuries had been regarded as simple structural features of both plants and animals,38 as purely mechanical devices with static or dynamic roles, suddenly emerged as elementary sentient units of living organisms as well. The exciting interest of this novel perspective was further boosted by the technological marvel of the day, the microscope, which showed fibers to be not only peculiar to but also seemingly ubiquitous in living matter. Already in 1656, according to Pierre Borel (1620?–1671), this optical instrument had showed that “the heart, the kidneys, the testicles, the liver, the lungs and the other parenchymas of the body are heaps of organelles and fibers.”39 Marcello Malpighi, who from the mid-1660s carried out studies with pieces of organs especially prepared for microscopic examination, described a similar pattern for the brain in general. He found that the “whole white portion of the brain is divided into small, almost round fibers,” which seemed to take their origin from a multitude of “minute glands” in the cortex.40 In fact, “An intimate connection and continuation between these cortical glands and nervous fibers is observed after boiling the brain.”41 A few years later, Malpighi discovered that plants are also wholly constituted by microscopic fibers as well as by “utriculi” or “sacculi.”42 Early in the following decade, Nehemiah Grew (1641–1712) concurred: “The most unfeigned and proper resemblance we can at present make of the whole body of a plant, is to a piece of fine bone lace, when the women are working it upon the cushion.”43 That same year the extraordinary Dutch amateur microscopist Antoni van Leeuwenhoek,44 following inspection of bovine muscle fibers pressed flat in front of his single-lens instrument (see Fig. 7.10), wrote to his British colleague Robert Hooke: From this it became clear, nay clearer than I can here represent, that the flesh-fibres in their turn consist of a great number of fibres, which for distinction I will call filaments. […] I gave my mind to this subject and now say that, since we see that a large muscle in its turn consists of many thousands of minute muscles, each enclosed in membranes, and that each flesh-fibre again consists internally of filaments, that each flesh-fibre is a muscle and that each filament (100 of which make a fibre) is in its turn a muscle of flesh comprising many vessels also enclosed in membranes.45 This bold conjecture was amply justified for Leeuwenhoek, who 6 years earlier had astonished the world with the revelation of a variety of incredibly tiny animals that appeared to him a thousand times smaller than the eye of a louse.46 Now, comparing dimensions in his careful study of muscle fibers, he recalls in amazement those “creatures which are thinner than one of the filaments of which a flesh-fibre is composed, and remember that such an animalcule must have a skin, veins, nerves and muscles, nay is as perfect as a large animal.”47 Page 12 of 22

Non-Spiritual Physiology I: The startling new evidence produced by microscopes, together with the slowly concocted unorthodox views about the irritability of fibers mentioned above, at last shook up the basic conceptions about the living world, leading to what later would be called a “paradigm shift.”48 From time immemorial the bodily fluids had been the absolute rulers of medical theory. In early days it was first the blood, which later became tied up with phlegm and two types of bile (yellow and black) as the four humors of Hippocratic doctrine, all of them in turn guided by or in some connection with several kinds of pneuma or its Latin equivalent, spiritus. These free-flowing and permeating components were always credited with promoting all of the organic functions, either rhythmically dilating the heart or carrying sensations and actuating the limbs, while at the same time nourishing or conditioning every bodily part. Indeed, good health (eucrasia to the Greeks) was seen as the equivalent of proper humoral balance, whereas sickness (dyscrasia) was thought to reflect humoral imbalance. Moreover, a slight constitutive (p.179) excess in one of the humors was believed to determine personal temperament and usual behavior. As a vestigial mark of such durable ideas, today we still refer to sanguine, phlegmatic, and choleric (from khole, meaning yellow bile) or melancholic (from melan-khole or black bile) personalities. The time had now come to recognize that the leading role in physiology corresponds to the solids of the body, rather than to the fluids, and getting rid of all those embarrassing contradictions posed by experience accumulated over the years. It had become clear that it is the heart that propels the blood, not the inverse, as proved by its power to continue beating in total isolation from the rest of the body (even from the blood) after being dissected out from a frog, for example. And it is the muscles that contract by themselves, even if uncoordinated, irrespective of the presence of a spirit-delivering brain, as observed in decapitated tortoises and snakes.49 In effect the solids of the animal body, typically organized as systems of fibers, are the ones that possess the property of self-movement, one of the great secrets of life. Thus a totally new and promising “solidist” physiology (as opposed to the former “fluidist” model) emerged and began to take shape. The leading exponent of this new vision was Giorgio Baglivi (1668–1707; Fig. 11.1), a former pupil of Malpighi who was born the same year as Herman Boerhaave. Although a native from what is today the Croatian city of Dubrovnik, Baglivi’s career developed fully in Italy, where he received medical education and graduated probably in Salerno.50 He then traveled actively, working for hospitals in different Italian cities, and settled finally at Bologna, where he became an assistant to Malpighi. When the latter moved to Rome, Baglivi followed him as a personal secretary, eventually becoming one of the physicians in charge of two popes.

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Non-Spiritual Physiology I: An obedient student while at the same time unsatisfied with inherited medical theory, Baglivi questioned established knowledge with indefatigable experimentation. Thus he made notable improvements over the simple techniques used by his professor when preparing specimens for microscopy. Apart from washing and boiling the sample pieces, Baglivi experimented by soaking or marinating them for various periods in liquids of different compositions and concentrations—wine or vinegar, alcohol, acids, milk, and so on.51 Most of these procedures were carried out in the hope of extracting nonessential substances that might obscure the true underlying structure of living matter. Inspecting such preparations with a high-quality microscope of “four lenses,” Baglivi confirmed that all solid parts of the animal body are fibrous, being able to witness this even in the fetal stages.52 According to Baglivi the fibers could be classified into two main types, depending upon the part of the body being considered. In one category he placed muscle, tendon, and bone, which are characterized by having basically parallel arrays of fleshy or “muscular” motor fibers, more or less infiltrated with blood (in muscle and tendon), or more or less mineralized by adsorption of salino-earthy particles (in bone). The second group included blood vessels, glands, nerves, and virtually all of the internal organs. These Baglivi found to consist of web-like arrangements of “membranaceous” fibers, which he believed are ultimately derived from the “dura mater” or outer fibrous membrane enveloping the encephalon and spinal cord. Needless to say, natural variations among individuals will be expected in their fibers, just like in any other anatomical feature, depending on age, gender, lifestyle, and other factors. Thus, for example, we read that fibers are softer in women than in men, in children than in adults, and in the French if compared to the Italians, although the fibers in the latter are still softer than those in the more rugged Spaniards and Africans.53

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Non-Spiritual Physiology I: (p.180) The two major types of fibers actually belong to two complementary motor systems, one of them related to the heart and the other to the brain, so that functioning together both integrate the overall activity of the animal body.54 The motor system centered in the heart is in charge of distributing the blood, which apart from its nourishing qualities performs a major role in muscle contraction (see below). The twin system is centered in the encephalon, where the rhythmic contractions of the dura mater

Figure 11.1: Giorgio Baglivi (1668–1707), once assistant to Marcello Malpighi and eventually a physician to Popes Innocent XII and Clement XI, inaugurated a revolutionary “solidist” vision of physiology in which bodily functions and malfunctions are understood primarily in terms of interactions among the structured anatomical parts, constituted mostly by fibers, rather than among humors, spirits, and other fluids. (Line engraving on the frontispiece opposite to the title page of his Opera omnia, 1714, by C. Duflos after an original portrait by Maratti; Wellcome Library, London, cat. M0008694)

produce an ebb-and-flow effect upon the nervous fluid (animal spirit) contained in the underlying minute glands discovered by Malpighi all over the brain’s cortex. Thus the dura mater now presses upon the minute glands, hence propelling their nervous fluid toward the periphery to promote various actions, whereas on relaxation at the next instant it draws or sucks back the fluid, which thus assists in bringing sensory impressions up to the brain.55 This idea of rhythmic contractions squirting nervous fluid or spirit out from the encephalon, we shall recall, had been around for quite some time. Already Jean Fernel had written about it, except that it was the brain itself rather than the meninges that contracted (see Chapter 5).

Nevertheless, vital movement is a property of the muscle fibers themselves, with the nervous fluid playing only a regulatory function. As explained in a later dissertation: having often and carefully examined the structure of the muscles…I began to assert that the principal, not to say the whole power of motion, or the force moving the muscles [potentiam moventem musculos], resides in the muscles themselves, that is, in the special fabric of the fibers […] and that the spirits flowing through the nerves serve no purpose other than to regulate their motions.56

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Non-Spiritual Physiology I: As regards the fluids, the blood is more immediately determinant of the moving power of muscle, though this is so because it contains numerous floating solids capable of producing irritation; indeed, its countless round globules can prod the muscle fibers to contract and at the same time greatly facilitate the relative displacements of those threads by serving as rollers in between them. Baglivi described this process with the help of a few sketchy pictures to illustrate how the regulation of

Figure 11.2: Baglivi’s illustration of the mechanism of muscle contraction, a (Baglivi 1714, p. 405, figure II [figures are labeled with Roman numerals in the original work, although references to them in the text are given in the Arabic system]). The diagram shows his conception of how muscle is organized at the microscopic level; five fibers are depicted, with rows of regularly spaced roller balls (blood globules) in between them. Since the roller balls are all of roughly spherical shape and equal size, being also regularly distributed, they cause an even irritation of the fibers, which therefore slide uniformly (AB edge to the right in relation to CD edge) and

movement depends on the variable diameter of the rolling globules. The explanation is given in the text as follows:

stay straight, so no net contraction occurs.

Fig. 2 [Fig. 11.2 here] represents a simple muscle, where AB [and] CD are fibres between which the blood balls run. The balls are in contact with both the upper and the lower fibres and the result is a two-fold pressure or waving. If the rolling balls are of the same diameter, as in the figure, the wave movement will be slight and regular and the contraction of the ends small, but if the diameter changes there will at once be an irregular wave movement in the fibres, a greater tension at the middle and a greater contraction in the end portions, as shown in fig. 3 [Fig. 11.3 here].57 The round blood globules can present variations in diameter and even get distorted to become ovoid or irregular. Consequently the globule-to-fiber contact surface, and therefore the extent of fiber irritation, varies all the time. As a result muscles “constantly try to contract.” Moreover, “Actually, the muscles would be in incessant movement if the antagonist muscles did not keep them in check, and it is only when this force is surmounted by nervous fluid [animal spirit] that muscular contraction results in visible muscular movement.”58

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Non-Spiritual Physiology I: Exactly how the nervous fluid or animal spirit tilts the balance between antagonist muscles to produce such an effect was admittedly a difficult problem for Baglivi. Nevertheless, he suspected that somehow the highly purified liquid has the ability to alter the shape of the blood globules, and thus to directly modulate the amount of their irritating interaction upon the fibers. Once again, as in the case of Glisson, animal spirit still played a role in this theoretical framework, but that role is now a secondary one, no longer the protagonist. The evidence in favor of an autonomous motile power in muscle fibers became so overwhelming that even the animists had to recognize its existence and eventually put it to work in their own theories. Thus we find Baglivi’s somewhat (p.181) older contemporary Georg Ernst Stahl, whom as seen in the previous chapter charged the soul again with directly controlling the functions of the living machine, making use of the intriguing independent property of muscle fibers to account for certain phenomena. Once the voluntary psychic or animal operations had been explained, he added:

Figure 11.3: Baglivi’s illustration of the mechanism of muscle contraction, b (Baglivi 1714, p. 406, figure III). The diagram shows two muscle fibers in between which roller balls (blood globules) of slightly varying sizes, shapes, and spacings can be appreciated. The

uneven geometry and distribution of the Now it only remains to make roller balls, induced possibly by an influx one single and last of nervous fluid (animal spirit), results in observation: that all the uneven sliding of the fibers that causes principal movements undulations and therefore shortening of ordinarily called vital, though the assembly. involuntary, which are executed over the whole extension of the body, do not have however but just one and the same kind of instrument, that is the contractility of the muscle fiber, especially destined to produce this effect.59 The new thinking in this domain of physiology could not be ignored by anyone attempting to build a no-nonsense, comprehensive medical science.

Concluding Remarks

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Non-Spiritual Physiology I: By the end of the 17th century, the Scientific Revolution sparked in the Renaissance had affected the understanding of living matter in a deep, very fundamental way. The organs, much as they differed in form and function, were all apparently built from similar tiny elements: fibers. And at least some of these basic constituents seemed to have a primitive life of their own, in the sense of detecting specific changes and directly responding to them. Either the fibers had minuscule souls, or else they behaved merely according to their nature (physis), independently of animistic (psychic) control. The first view was held by Gottfried Leibniz, the German philosopher who battled Stahl’s simple-minded animism.60 Increasing numbers of scientists, however, were attracted by the possibility that life could be a largely physical phenomenon. Thus organisms, which for centuries were conceived as strictly non-divisible units, each ruled in toto by its respective soul, started to be seen as assemblies of organs that under certain conditions could be taken apart and separately studied for some time. This was the revolutionary approach taken, for example, by Jan Swammerdam in the mid-1660s,61 when he devised using an excised muscle in a glass vial to critically test the idea that muscles would swell while contracting, and also by Marcello Malpighi when he could directly observe the blood passing from arteries to veins through capillaries in a living lung placed under his microscope. These methods were clearly different from the occasional sectioning of a muscle in half by Galen to show that the two parts could still shorten by themselves, or from his demonstration of how a squealing pig could be muted by cutting a nerve in its neck, and also from Leonardo’s instantly destroying the life of a frog with a pointed probe driven through its vertebral column. The new brand of researchers attempted to intervene in living bodies in a less crude and more systematic way, not only in order to better inspect their structure with a more lucid insight like the anatomists, but also looking for its working processes with inquisitive and objective minds. Experimental physiology had been born. An exciting host of novel ideas and possibilities followed these developments, ushering in the elegantly confident intellectual atmosphere of the 18th century. Everything could be properly understood, at least in principle, given enough time and clever, disciplined thinking. Among the few pending enigmas were the nature, or physis, of fibers in the animal body, and the mechanisms of irritability —the subjects of our next chapter. (p.182) Notes:

(1) Although not in the radical sense of considering them incapable of feeling as it is often misinterpreted. See also Chapter 6. (2) See Chapter 10.

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Non-Spiritual Physiology I: (3) Aristotle, On the Soul, I, 2, 405a20–21; DK 11 A 22 (Barnes, 1995, vol. 1, pp. 645–646); for reference to authors of classic Greece see also Chapter 1. (4) Plato, Timaeus, 77b-c (trans. Zeyl, ed. Cooper and Hutchinson, 1997, p. 1277). The tripartite model of soul according to Plato is discussed in Chapter 1. (5) Ibid. (6) Aristotle, On the Soul, II, 2–3, 413a21–414b1 (Barnes, 1995, vol. 1, pp. 658– 659). Animal embryos possess just the nutritive faculty, like plants, so at that stage of development also animals are endowed only with the simplest soul; see Aristotle, Generation of Animals, II, 3, 736a31–35 (Barnes, 1995, vol. 1, pp. 1142–1143). (7) Galen, Natural Faculties, I, 12 (Brock, 1952, pp. 44–47). (8) Ibid., I, 1 (Ibid., pp. 2–3). Galen’s work related to animal spirit is discussed in detail in Chapter 2. (9) Ibid., III, 12 (Ibid., pp. 284–285). (10) Ibid. (Ibid., pp. 288–289). (11) Galen, Usefulness of the Parts, V, 11 (May, 1968, vol. 1, p. 267). (12) Ibid., 9 (Ibid., p. 263). (13) Ibid., 10 (Ibid., pp. 264–265). (14) Galen, Natural Faculties I, 4 (Brock, 1952, pp. 16–17). (15) Galen, On the Affected Parts, I, ch. 7 (Siegel, 1976, pp. 41–42). (16) Galen, De motu musculorum, I, 8 (see trans. Goss, 1968). (17) For more on Vesalius’ work see Chapter 5. (18) Vesalius, 1543, De humani corporis fabric libri septem, book III, Chapter 1, pp. 257bis-258bis (Richardson and Carman, 2002, p. 3). See also Temkin, 1965. (19) See Chapter 7 for other aspects of Harvey’s contributions to this story. (20) Harvey, 1651, Anatomical Exercises on the Generation of Animals, Exercise 57 (Willis, 1990, p. 455). (21) Ibid. (Ibid., p. 457). The “sensitive plant” refers to Mimosa pudica, a herb imported from the New World that caused great excitement and puzzlement in Europe due to the remarkable property of folding its leaves inward when touched, and slowly extending them back again after a few minutes. Page 19 of 22

Non-Spiritual Physiology I: (22) Ibid. (Ibid.) (23) Ibid., Exercise 51 (Ibid., pp. 430 and 431). (24) Ibid., Exercise 57 (Ibid., p. 457). (25) For a discussion on the influence of Harvey on Glisson, see Pagel, 1967. For a review of Glisson’s career see Walker, 1971. His work regarding animal spirit is reviewed in Chapter 8. (26) Glisson, 1654, p. 396; quoted in Temkin, 1964, where the historical origins of the term “irritation” are traced back to antiquity. For a different view on the history of irritability see Verworn, 1913, pp. 1–17. (27) This theory became the subject of a whole treatise on the philosophy of living matter (Glisson, 1672). For a detailed essay on this development see Giglioni, 2002. (28) At this time, 15 years before the publication of Newton’s Principia, someone might reason for example that a stone falls every time it “perceives” (thanks to a perceptio materialis [i.e., the lowest grade of perception]) an opportunity for satisfying an intrinsic and inextinguishable appetite for resting in as low a position as possible. (29) Relevant compact explanation found in Glisson, 1677, Chapter IX, pp. 195– 199. (30) See Chapter 6. (31) Stensen, 1667, p. 4 (Collins et al., 1994, p. 97). See also Chapter 7. (32) Ibid., pp. 56–57 (Ibid., pp. 200–203). (33) Mayow, 1674 (Brown and Dubbin, 1907, pp. 282–284). See also Chapter 8. (34) This view constitutes a philosophical position known as hylozoism, which is sometimes confused with vitalism (i.e., the idea that life is due to some vital force other than physicochemical processes). To a large extent hylozoism (i.e., the idea that matter can become alive if it is organized in the proper way) is actually the opposite of vitalism. (35) Glisson, 1677. (36) Glisson, 1677, VII, 2, p. 169. See translation in Clarke and O’Malley, 1968, p. 168. (37) Ibid., 1, p. 169.

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Non-Spiritual Physiology I: (38) For a classical comprehensive historical review of fiber theory see Berg, 1942. Shorter and updated accounts are available at Grmek, 1970, and Frixione, 2000a and 2004. (39) Borel, P. (1656) Observationum microcospicarum [sic] centuria. The Hague. Quoted in Grmek, 1970 (translated here from the French original). (40) Malpighi (1665) De cerebro. See partial translation in Meyer, 1967. For more on Malpighi see Chapter 7. (41) Malpighi (1666) De cerebri cortice. See partial translation in Meyer, 1967. Considering the crude procedures for specimen preparation and the primitive optical conditions of microscopes used by Malpighi, most of the “fibers” he saw were probably bundles of actual nerve fibers. For a detailed technical discussion of this matter see Clarke and Bearn, 1968. (42) Malpighi (1671/1674) Anatome plantarum. London. (43) Grew, N. (1682) Anatomy of Plants. London. Quoted in Singer, 1989, p. 159. (44) For other aspects of Leeuwenhoek’s role in this story see Chapter 7. (45) Van Leeuwenhoek, 1682 (Collected Letters…, 1948, pp. 396–397). An equivalent account would be independently communicated years later to the Royal Society of London by Wijer Muys (1682–1744); see Muys, 1714. For Van Leeuwenhoek’s findings about nerve structure see Chapter 7. (46) Van Leeuwenhoek, 1676 (Collected Letters…, 1941). (47) Van Leeuwenhoek, 1682 (Collected Letters…, 1948, p. 397). (48) A “paradigm shift,” a technical term introduced by Thomas Kuhn (1962) to denote a key element of scientific revolutions, means looking at the same things in an utterly different and novel way, like in those ambiguous pictures where two unrelated figures can be identified in the same image depending solely upon the mental attitude. (49) For an example of contemporary discussion of these facts see Stensen, 1667, pp. 58–59 (Collins et al., 1994, pp. 205, 207). (50) For a compact profile of Baglivi, see Grmek, 1981. His main work is briefly reviewed in Grmek, 2000. A more extensive study can be found in Toscano, 2004. (51) Baglivi, Specimen libri primi De fibra motrice, II. In: Opera omnia medicopractica et anatomica, 1714, p. 266. (52) Ibid., I, p. 263. Page 21 of 22

Non-Spiritual Physiology I: (53) Ibid., 265. (54) Ibid., V, pp. 272ff. (55) For a detailed discussion of Baglivi’s conceptions about the reciprocal mechanical interactions of the dura mater and the nervous fluid or animal spirit, see Toscano, 2004, pp. 115–122. (56) Baglivi, De anatome fibrarum, et de morbis solidorum, In: Opera omnia medico-practica et anatomica, 1714, p. 401. The English translation is taken here from Vartanian, 1960, p. 235. Latin expression not included in the translation quoted here. (57) Ibid., p. 405. The English translation is taken here from Bastholm, 1950, pp. 184–185. (58) Ibid., p. 406 (trans. Bastholm, 1950, p. 185). (59) Stahl, 1708, pp. 474–475; quoted in Vartanian, 1960, p. 235 (translated here from the French original). Italics as in the source. (60) See Chapter 10. (61) See Chapter 7.

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Non-Spiritual Physiology II:

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Non-Spiritual Physiology II: Irritable Fibers C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0012

Abstract and Keywords This chapter is concerned with the fast development of the notion of irritability during the 18th century. This developed through the envisioning of various sensitive-motive “principles” found within the body and the creation of an elaborated theory of fibers. It discusses the influential work of Albrecht von Haller, who changed the concepts and methodologies of the physiology of the neuromuscular system forever. This chapter notes that it is Haller and his work on irritability that marked the arrival of irreversible decline for the idea of animal spirit. Keywords:   irritability, sensitive-motive principles, theory of fibers, Albrecht von Haller, physiology, neuromuscular system, animal spirit

Irritation, is a Species of Stimulus, expressing a lesser Degree of it than Vellication, or Corrugation. Quincy, 1722, Lexicon Physico-Medicum, p. 224. I call that part of the human body irritable, which becomes shorter upon being touched; very irritable if it contracts upon a slight touch, and the contrary if by a violent touch it contracts but little.

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Non-Spiritual Physiology II: Haller, 1755, A Dissertation on the Sensible and Irritable Parts of Animals (Tissot M, trans.), p. 4 (p. 8 in Temkin, 1936 ed.). [F]iber is to the physiologist what line is to the geometrician. Haller, Elementa physiologiae, 1757, Book 1, Section 1, p. 2. The new thinking in the physiological domain just described in the previous chapter was an uneasy legacy from the 17th century to the next. From a certain perspective it was intellectually exciting, since the secrets of life seemed closer at hand than ever before. The Cartesian dream of robot-like mechanical organisms, greatly supported by the demonstration of the heart being a pump that keeps the blood moving continuously in a circle like a wheel (even if Harvey himself counted among those who laughed at Descartes’ model of animal bodies as automata), plus the notion that localized solid fibers rather than ubiquitous diffusible fluids are the main actors of life processes, and the invention of an optical instrument capable of revealing the so-far-hidden arrangements of those very fibers in different organs: all of it constituted a scenario in which discovering the remaining mysteries was perceived as just a matter of time. The optimistic stance was not too different from our own in recent years upon the full description of the human genome. In contrast to current molecular biology, on the other hand, that promising outlook implied an imposing challenge, for it meant pushing aside nearly all previous theories and replacing them with alternative explanations. Physiology, and therefore its inseparable siblings of interest in medical practice, pathology and therapeutics, needed to be built up again in an almost piece-by-piece fashion. The advancement in the entire field of the health sciences could no longer be a result of occasional incremental steps like it had always been before, ever since the treasure of ancient Greek knowledge was gradually discovered in the late Middle Ages. Now the foundations of medicine were jumbled up to the point that the very concept of “disease” was in need of redefinition. Such was the price of a true revolution in science.

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Non-Spiritual Physiology II: Last but certainly not least, the new perspective about living things was mildly frightening to physicians and other scientists. Just how much of the psychical realm would end up being downgraded to the physical level, as it had happened already with the animal spirit during the 17th century? What if, as was the case with the animal spirit, other psychical realities were again called into question and even referred to as lexical relics, to be understood as really akin to the vapors of salt or wine? What if, following this trend, research would show that animal life can indeed be explained wholly in mechanical terms, as Descartes had claimed? What would then be the ontological status of the human body and soul? True, reasoning capacity could still be invoked as an exclusive human faculty, as proof of man’s soul. But how should “reason” be understood in this context, so that a sharp demarcation could be established in relation to clever dogs that can learn an endless series of tricks, or sharp wild foxes capable of outsmarting not only turkeys and hens but hunters as well? Physiology had become an attractive but particularly difficult and troubling beast, and no one could help it. Nor anyone attempting to build a no-nonsense, comprehensive theoretical framework for medical science could afford to ignore it, of course. Inevitably the novel, handsome maverick was destined to remain a misfit, even in the hands of the master of eclectic conciliation at Leiden, Herman Boerhaave.

Boerhaave and his Disciples The celebrated Dutch professor, whom we met already in Chapter 10, derided Baglivi’s model of how the nervous fluid (p.184) is set in motion by contractions of the dura mater, pointing out that this outer membrane wrapping the encephalon simply cannot move because it is so firmly attached to the interior surface of the skull that its vessels become imprinted on the bone.1 Nevertheless, Boerhaave and his pupils accepted the idea that fibers are the distinctive ultimate units of all living matter, in which they behave as structural or mechanical devices. In fact, he starts explaining his theoretical foundations of physiology with the assertion that human anatomy “is composed of solid and fluid Parts,”2 and continues immediately in the following paragraph with a definition of the former: The solid Parts of the human Body are either membranous Pipes, or Vessels including the Fluids, or else Instruments made up of these, and more solid Fibres, so formed and connected, that each of them is capable of performing a particular Action by the Structure, whenever they shall be put in Motion…and the Faculty of performing various Motions by these Instruments, is called their Functions; which are all performed by mechanical Laws, and by they only are intelligible.

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Non-Spiritual Physiology II: Despite the priority assigned here to the solids, though, Boerhaave declares just a few pages later that the mechanical laws he is referring to are those of the fluids—that is, “the Laws or Principles of Hygrostaticks, Hygraulics, and Mechanics.”3 This is confirmed in a note to this paragraph: “All Motions in the human Body proceed primarily from the Fluids; the Bones are moved by the Muscles, the Muscles by their Nerves, and other Vessels, and these again by their contained Fluids.”4 In fact, Boerhaave was never fully clear or explicit as to the origin of movement in the living body. This is indeed remarkable for a rigorous analyst of such caliber and seems to betray a fundamental uncertainty about the essence of life itself that may have bothered him for years.5 Late in his career he taught that while one should attempt to understand the motion of the animal body as a machine in Newtonian terms, the immediate cause of that motion is a different question. He then goes on to state, in vintage Cartesian parlance, that once the machine is properly built and adjusted, “one single impulse is given to it which suddenly imparts motion to the whole and causes this to continue.”6 Yet many examples were known in which the living machine could be wholly dismantled and still its isolated organs or even fragments of the latter continued to show signs of independent activity. Boerhaave specifically recognized (albeit without further comment) that in the heart, the primary motor for all fluids in the body, there seems to be “a latent and surprizing [sic] Propensity to contract and dilate alternately; even so as often to move in that Manner after the Animal is dead, and itself taken out of the Body, and even after it has been cut in Pieces.”7 In a public lecture delivered 2 years before his death, he had no choice but to admit that this property of the heart should also be taken into consideration. In his words: “I will call it its irritability, and by this name I understand its innate aptitude due to its fabric, thanks to which it easily and promptly contracts upon” appropriate stimulation.8 As we shall see below, some of Boerhaave’s talented pupils, while broadly supporting their great professor’s theoretical edifice, would try to find their own ways of explaining or dealing with the enigma of the original source of vital power. At any rate, it became clear that the structural organization of a living body is sustained by solid fibers that, like everything else according to the recently refurbished classic theory about matter, ultimately consist of immutable, indivisible, elementary submicroscopic corpuscles or atoms.9 And when we come to living things,

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Non-Spiritual Physiology II: Chemistry, then, alone informs us, that the first Elements of which the solid parts of the Body are compounded, are a mere Earth firmly united together by an oily glutinous matter, which cannot be separated from them but by the extreme force of an open Fire. ’Tis [sic] teaches us too, that Water also insinuating itself among these Elements, serves to bind them together, and being consolidated and concreted with them will not be expelled without a great deal of difficulty.10 But the clue to really understanding living matter stems from the actual arrangement of those earthy first elements in space. According to Boerhaave’s medical syllabus, translated from the Latin as Aphorisms Concerning the Knowledge and Cure of Diseases, the simple earth particles are aligned and glued to each other in rows so as to make up minimal fibers (Fibram minimam)11 —that is, the elementary structures of all solid parts in a living body. This subject was examined in more detail by one of his outstanding pupils, Gerhard van Swieten (1700–1772), who at one point was postulated as Boerhaave’s successor in Leiden, though he eventually moved to the University of Vienna. Once there, Swieten obviously felt that some of his teacher’s ideas were in need of further clarification beyond what could be found in the books, and he tried to help in this endeavor by perusing his own notes taken as a student and then writing extensive “commentaries” to Boerhaave’s Aphorisms. In these detailed explanations we learn that two or more minimal fibers or linear chains of earthy particles can adhere to each other laterally as a monolayer, thus constituting the (p.185) most delicate kind of membrane (Fig. 12.1).12 Such minimal membranes, when curled up into tiny cylinders, constitute the thinnest category of vessels. And since a filled-up unit of the latter is in fact a fiber of a second order, it can in turn associate sideways with other similar fibers as a second-order membrane, which rolled up into a tube becomes a fiber of the third order when full. This modular grouping pattern is repeated again at higher dimensional orders, until coarser fibers are produced that can interweave and form the relatively thick membranes limiting the largest arteries and veins (or equivalent channels in plants), as well as other hollow organs. The basic stages of this structural hierarchy were aptly illustrated by the surgeon Johannes de Gorter (1689–1762; Fig. 12.2), another distinguished disciple of Boerhaave’s. He discussed at length the construction and organization of such fiber structures in the first pages of his compendium on medicine (Fig. 12.3).13 Nevertheless, he disagreed with the

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Non-Spiritual Physiology II:

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Non-Spiritual Physiology II: (p.186)

Figure 12.1: Modular construction of fibers of different calibers, according to Boerhaave’s school. The successive stages B to E are shown in side view (left) and end view (right). Earthy particles link to one another in linear fashion (A) to constitute tiny minimal fibers (B). The latter can then associate sideways to form delicate sheets or minimal membranes (C), which curling up into closed cylinders constitute minimal tubules or fibers of the second order (D). These can in turn associate sideways to make up membranes of the second order (E), which form vessels or fibers of the third order (F). Higher levels in this hierarchy constitute the macroscopic membranes and vessels found in different organs.

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Non-Spiritual Physiology II: gross mechanical action assigned by Boerhaave to the animal spirit. Instead, de Gorter gradually arrived at the idea that all living matter possesses some kind of “motu vitali,” which becomes expressed through the activation of an intrinsic potential for movement (potentia movendi).14 In the case of muscle, the activation does depend on the influx of animal spirit, but there was simply no way that the latter alone could account for the largescale phenomenon of contraction. This conception, apparently the product of de Gorter’s independent reasoning, is almost indistinguishable from that of Glisson’s irritability.15

The Enormôn and Other “Principles” Looking for an appropriate word to denominate the intriguing capacity of living matter to respond autonomously to stimuli soon became part of the problem of theorizing about it. Several authors opted for the term “principle,” which really meant nothing, although it had the advantage of having a semantic resonance with the notion of arché or primordial substance of early philosophy in venerable antiquity.16 Boerhaave, among his old-age efforts to find a satisfactory conciliation between iatrophysical theory17 and the (p.187)

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Figure 12.3: Johannes de Gorter’s illustration of modular fiber construction, as shown on a plate in his Medicinae compendium, 1751, in which the elementary earthy particles are depicted elongated instead of round (cf. Fig. 12.1 above).

Figure 12.2: Johannes de Gorter (1689– 1762), a brilliant though somewhat dissident Dutch pupil of Boerhaave’s, on the frontispiece opposite to the title page of his Medicinae compendium, 1751. (Line engraving by J. Houbraken, 1735, after an original portrait by J. Quinckhard)

Non-Spiritual Physiology II: observed facts of intrinsic motion in isolated animal parts, tried to position himself on safe ground by invoking the concept of an “impetum faciens”18 (impetus making), that some Hippocratic physicians, as well as Galen, had used in classic antiquity.

The Latin term that acquired currency to express this idea in the 18th-century medical language was chiefly “enormôn,” a word derived apparently from the Greek “hormônta” or moving power.19 Boerhaave’s nephew, Abraham Kaau-Boerhaave (1697–1770), put the name into wider use by writing an essay on the topic.20 But it was mainly Hieronymus (Jerome) David Gaub (called Gaubius, 1705–1780; Fig. 12.4) who would insist on recovering

Figure 12.4: Hieronymus David Gaub

the ancient word,21 and who championed its modern application.

of Boerhaave’s who popularized the term enormôn to denominate a principle that

A chemist and a physician, as well as the actual translator of Swammerdam’s Biblia naturae

http://commons.wikimedia.org/wiki/ File:Hieronymus-David-Gaub.jpg)

(1705–1780), a German chemist and physician also known as Gaubius, a pupil

energizes the biological machinery of the body. (Portrait by H. van der My, 1741;

from Dutch into Latin,22 Gaub was close to Boerhaave, who supervised for him a dissertation on the true nature of the solids. The Boerhaavian training of the pupil in chemistry shows in his discussions of bodily materials, where we read that the earthy parts of these substances are “the basis and stabiliment [sic] of the whole machine.”23 To attain such stability, however, the particles necessarily have to be held together by indispensable glutinous particles.24

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Non-Spiritual Physiology II: Now, in order to perform the functions of life, the solids need to be energized, and this Gaub believed is due to that “impetuous principle in the body,” the enormôn. This, however, could also explain health disorders through becoming faulty either by excess or by deficiency: “The latter I call torpor, the former irritability.”25 Therefore irritability is not in this context a property but merely a pathological condition of living matter: “Irritability, as I understand it, is when the sensibility of the living solid is so great, that upon the slightest irritation it breaks out into such violent motions as disorders the tenor of the functions.”26 Nevertheless the impetuous agent or driving force itself was considered to be the most outstanding feature of the living body, perhaps deserving of the name life itself. It is the principle of motion of all parts of the body, from which all of those movements spontaneously carried out by the body in the absence of awareness of the mind are derived; it seems also to cause the residual twitching seen in parts of living creatures cut off or torn away.27 In Gaub’s view, the enormôn is coextensive with the nervous system throughout the body; therefore, its main seat is the encephalon, from where it stretches down along the spinal cord and out through the nerves. Consequently, it represents a sort of internal skeletal figure within the body, “a neural man” or “kind of man within a man.”28 Still, this enormôn of the body is harmonized and perhaps unified with an enormôn of the mind, so it “can therefore be regarded as a kind of intermediary through which the mind and the organs of the body communicate.”29 This communication provides the substrate for Gaub’s main contention: that medical actions upon the body could also influence the mind and therefore the soul. In other words, that what had so far been reserved to the psychic sphere could become another department of physic. Neither “animal spirit” nor “irritability,” in the common understanding of this word at the time, is found in this picture of psychosomatic medicine. However, Glisson’s hylozoistic conception of an intrinsic vital force in living matter,30 essentially independent from the mind even if largely controlled by the latter through the nervous system, is clearly present in Gaub’s enormôn.

Mechanizing the Soul The idea of an autonomous capability for motion in living matter, though framed in a quite different perspective, (p.188)

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Non-Spiritual Physiology II: was put forward almost at the same time by another former disciple of Boerhaave’s, the notorious French physician and visionary Julien-Offray de La Mettrie (1709–1751; Fig. 12.5).31 This author so outraged his countrymen in 1745 with the publication of a book titled “Natural history of the soul” (Histoire naturelle de l’âme), where mental faculties are presented as the product of organic changes in the brain, that shortly after he was forced to flee France and take refuge in the far more open-minded Leiden, where people knew him from his student days at the medical school.

Unrepentant, 2 years later La Mettrie published his still more famous book L’homme machine, in which the standard list of movements observed in freshly decapitated animals, excised hearts, and isolated muscles is presented as ample evidence proving “in an incontestable manner that each small fiber or part of organized bodies moves by a principle of its own, the action of which does not depend of nerves like the voluntary movements.”32 Then, from this conclusion and in full alignment with the major trend of current medical thought that we have seen in the above paragraphs, La Mettrie gears up and argues forward to a sweeping consequence: “the soul is but a principle of movement, or a

Figure 12.5: Julien-Offray de La Mettrie (1709–1751), still another pupil of Boerhaave’s, was a French physician and very original writer whose important but daring books—particularly his L’homme machine—irritated the high ranks of political and ecclesiastical power, first in his home country and then in Holland. Several of the authors who are also discussed in these pages, like Hieronymus David Gaub and Albrecht von Haller (see below), felt abused in print by their colleague and took personal offense to many of La Mettrie’s outright materialistic views. (Line engraving by G.-F. Schmidt, after an original portrait by M. Quentin de La Tour; public domain picture, freely available at http:// commons.wikimedia.org/wiki/ File:Julien_Offray_de_La_Mettrie.jpg)

sensitive material part of the brain that one can, without fear of error, regard as a principal spring of the whole machine.”33

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Non-Spiritual Physiology II: We can easily understand why this sort of declaration equating the immortal soul with a springy part of the corruptible material brain, issued in a provocative and almost cheerful style, was quite more than even many relatively liberal 18thcentury minds were prepared to handle. La Mettrie’s inherently advanced thinking could hardly bring his contemporaries along to such an optimistic peek into the future. L’homme machine was ordered burned and banned, whereas its author now could not even remain in the comparatively tolerant Holland. Ultimately he obtained political asylum in Berlin, under the safe protection of the powerful Prussian king, Frederick the Great. Not even La Mettrie’s more independently minded colleagues could go along with his radical materialistic views allegedly based on the implications of modern medicine. Gaub, in particular, was deeply embarrassed that La Mettrie cited several clinical cases mentioned by the former in his own work, just to put them in support of theses with which the German author did not agree. The situation became so uncomfortable for Gaub that 16 years later he decided to produce a revised edition of the lecture that La Mettrie had freely abused, in order to rebut the scandalous opinions contained therein. Right from the starting lines of the new version Gaub confessed: I do indeed regret bitterly that a little Frenchman—a Mimus or Momus? [sic]— brought forth a repulsive offspring, to wit, his mechanical man, not long after sitting before this chair and hearing me speak, and did this in such a way that it seemed to many people that I had furnished him with, if not sparks for his flame, at least matter for embellishing his monstrosity.34 In a more relaxed vein, Scottish professor of medicine Robert Whytt (1714–1766; Fig. 12.6), a younger but significant alumnus of Boerhaave’s school,35 quietly converged on selecting the same words used by La Mettrie for the above definition of the soul—a principle of movement and sensitivity—but with a distinctive twist: Whytt’s active sentient principle is associated with, rather than being just a part of, the body. In practice, however, it is an incorporeal potency just like Gaub’s enormôn: “we cannot but acknowledge,” wrote Whytt, “that he [‘the all-wise AUTHOR of nature’] has animated all the muscles and fibres of animals, with an active sentient PRINCIPLE united to their bodies, and that, to the (p.189)

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Non-Spiritual Physiology II: agency of this PRINCIPLE are owing the contractions of stimulated muscles.”36

The two faculties of this principle (i.e., acting and feeling) are exactly those of the nervous system and also those of the soul. Accordingly, Whytt was “inclined to think that the anima and animus, as they have been termed, or the sentient and rational soul, are only one and the same principle acting in different capacities.”37 Needless to say, he was as puzzled as Boerhaave and many others by the seemingly autonomous motions displayed by headless animals or their isolated body parts. And, as the leading physiologist that Whytt was, there was no question in his mind that those movements “are owing to one and the same cause, viz. an irritation of their fibres or nerves.” Responding to irritation implied in the first place feeling the stimulus, however, and Whytt was convinced that “feeling is not a property of matter.” This is where the sentient faculty of the principle that he proposed was required, and he had a rational explanation for the

Figure 12.6: Robert Whytt (1714–1766), an outstanding Scottish physiologist and professor of medicine at the University of Edinburgh, hypothesized that an illdefined “active sentient principle” mediates reflexes and coordinates bodily movement in general. He was to sustain a protracted controversy on this subject with his Swiss colleague Albrecht von Haller, reviewed below. (Detail of oil painting by G. Bellucci, 1738, currently at the Royal College of Physicians, Edinburgh; Wellcome Library, London, cat. 0008120)

enigmas still surrounding these facts, in which he clearly distinguished what was known from what was not. To quote: it must follow that the motions of the heart, and other muscles of animals, after being separated from their bodies, are to be ascribed to this [active sentient] principle; and that any difficulties which may appear in this matter are owing to our ignorance of the nature of the soul, of the manner of its existence, and of its wonderful union with, and action upon the body.38 Page 13 of 31

Non-Spiritual Physiology II: Perhaps elegant, but going back again to ill-defined, mysterious soul-like agents as Gaub’s enormôn, or Whytt’s “active sentient principle,” seemed like no scientific explanation at all to many of their contemporaries in an “Age of Enlightenment.” Then again, no one could safely buy into La Mettrie’s doctrines either. A minimum of real light was badly needed for getting over this intellectual impasse on a most crucial topic. Here indeed was a task for a giant in physiology.

Not all Fibers Are Created Equal As discussed above, nearly all of Boerhaave’s pupils who were authors of note at the time endorsed, in one way or another, the novel hypothesis that living matter is equipped with an inherent capacity to move by itself in response to irritation. A question lingering in everyone’s mind, however, was whether all parts of the body are equally endowed with such capacity. The simple and general facile answer was that every fiber in the body is in some way sensitive as well as dynamic. Yet it was evident that whereas all types of muscles (i.e., skeletal, cardiac, gastrointestinal) are supremely irritable, the equally fibrous bone seemed quite unresponsive to stimulation. And what about other parts like tendons, ligaments, skin, glands, internal organs, or even the various components of the nervous system itself? Further, if muscle is so irritable in its own right, what was the exact function of the nerves and their animal spirit content in activating motion? No one knew for sure the correct answers to these questions, because providing them would have required a patient and thorough examination of different body parts in diverse animals. This challenge was squarely confronted by the Swiss-born but Prussian-based physiologist Albrecht von Haller (1708–1777; Fig. 12.7) with the help of Johann Zimmermann (1728–1795), an advanced student in his laboratory. Generally considered as the most influential of Boerhaave’s pupils,39 Haller complained that “the great source of error in physic has been owing to physicians, at least a great part of them, making few or no experiments, and substituting analogy instead of them.”40 A particularly troubling instance of those errors, he continued immediately, was that some celebrated authors have laid hold of the first notions of Irritability, so as even to make use of this property of our fibres…as a basis of almost an universal system of motion in the human body, and thence deduce the (p. 190)

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Non-Spiritual Physiology II: functions of the fibres, vessels, nerves, muscles, and in short of all our organs.

Thus Haller understood clearly the power of experimentation, and he was not one to be satisfied with just a few attempts here and there.41 In just a single year he and his assistant examined irritability and sensibility throughout the anatomies of 190 living animals, on top of similar work carried out in the previous years. Their results were rated according to strict qualitative and semiquantitative definitions, as famously described by Haller himself: I call that part of the human body irritable, which becomes shorter upon being touched; very irritable if it contracts upon a slight touch, and the contrary if by a violent touch it contracts but little.

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Figure 12.7: Albrecht von Haller (1708– 1777), a major Swiss figure of 18thcentury medical research, succeeded in providing a revised account of the structure and function of animal bodies in his Elementa physiologiae, which in many ways superseded the classic Institutiones medicae written by his professor Boerhaave, which Haller had edited and complemented with explanatory comments himself. Such advancement was the product of a systematic experimental approach that allowed him, among many other achievements, to map the properties of sensibility and irritability in the animal body. (Detail of mezzotint by J. Haid after an original portrait by C. Eberlein, 1745; Wellcome Library, London, cat. V0002516)

Non-Spiritual Physiology II: I call that a sensible part of the human body, which upon being touched transmits the impression of it to the soul; and in brutes, in whom the existence of a soul is not so clear, I call those parts sensible, the Irritation of which occasions evident signs of pain and disquiet in the animal. On the contrary, I call that insensible, which being burnt, tore, pricked, or cut till it is quite destroyed, occasions no sign of pain nor convulsion, nor any sort of change in the situation of the body.42 In the first pages of this seminal treatise Haller defensively admits to having exercised “a species of cruelty for which [he] felt such a reluctance, as could only be overcome by the desire of contributing to the benefit of mankind, and excused by that motive which induces persons of the most humane temper, to eat every day the flesh of harmless animals without any scruple.” The importance and impact of this work cannot be overstated for several reasons that bear mentioning. First, because of the social revulsion elicited by both the nature and the sheer scale of the methods applied to obtain the data. Second, because of the overwhelming amount of experimental labor invested in the project, which by itself set a new standard in physiological research. Third, because the results established that not all fibers are irritable or sensible. In fact, it turned out that only muscle fibers are irritable in Haller’s strict interpretation of the term, whereas only those parts supplied with nerves show sensibility. Not only were all these factors striking enough in themselves, but in addition this landmark in the history of physiology was destined to become the focus of bitter controversy on several fronts. To start with, Haller had to face the misfortune that his name became associated with the outrageous escapee La Mettrie, after the latter maliciously dedicated L’homme machine to him in an introductory piece dealing mostly with the voluptuousness of the senses.43 But while distancing himself from that hated materialist philosopher-physician, Haller had at the same time to acknowledge publicly that his findings called for a full revision of basic conceptions about how the whole body machine works, and therefore to define, again, the problem of the sovereignty of the soul. Haller, for one, though a very pious man, harbored no doubts about the fundamental independence of the material body:

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Non-Spiritual Physiology II: a finger cut off from my hand, or a bit of flesh from my leg, has no connexion with me, I am not sensible of any of its changes, they can neither communicate to me idea nor sensation; wherefore it is not inhabited by my soul nor by any part of it; if it was, I should certainly be sensible of its changes. I am therefore not at all in that part that is cut off, it is intirely [sic] separated both from my soul, which remains as entire as ever, and from those of all other men. The amputation of it has not occasioned the least harm to my will, which remains quite entire, and my soul has lost nothing at all of its force, but it has no more (p.191) command over that amputated part, which in the mean while [sic] continues still to be irritable. Irritability therefore is independent of the soul and the will.44 Furthermore, feeling himself forced to advance a hypothesis about the possible mechanism of muscle fiber contraction in response to irritation, but constrained to choose between the two single components of fiber structure in Boerhaavian chemistry—that is, inert earthy particles and glutinous linkages between them— his selection was inevitable and spiced with Newtonian flavor: “What therefore should hinder us,” Haller writes, “from granting Irritability to be a property of the animal gluten, the same as we acknowledge attraction and gravity to be properties of matter in general, without being able to determine the cause of them.”45 This position was sharply ridiculed by Whytt, whom Haller mentioned several times in proximity to the animism of the Stahlians for having recently published that nerve physiology involves a principle almost undistinguishable from the soul (see above). In an essay that included Haller’s name in its very title, Whytt asked: “if irritability be a property of the muscular glue, why may not sensibility and intelligence be properties of the medullary substance of the brain?”46 The Scottish professor’s stand as regards the primary source of animal motion was one of prudent recognition of ignorance, also bringing up an obvious reference to the highly prestigious Newtonian physics in support of his viewpoint: “if we are far from understanding the communication of motion and other actions of matter upon matter, how shall we be able to comprehend the manner in which an immaterial principle acts upon it?”47 In effect, each of these two great physiologists accused the other one of being overly simplistic, either by basing all explanations for a difficult problem on something purely metaphysical (Whytt’s “active sentient principle”), or else on something too elementarily physical (Haller’s gluten). This Whytt–Haller quarrel went on for years, and it was not the only one.48

Spiritual Distress

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Non-Spiritual Physiology II: Authors of the next generation who were active in the field during the 1770s and 1780s either sided with Haller or combated him (see below), in the wake of the publication of a treatise that was widely considered the replacement of Boerhaave’s classic Academical Lectures as the main reference in the medical sciences—that is, Haller’s monumental Elementa physiologiae corporis humani (1757–1766). Here he established his definitive legacy, in which irritability figured prominently with detailed reviews of all its properties and examples of the phenomenon of irritation.49 Nevertheless, this work approaches muscle physiology in more restrained terms than his earlier studies on the subject,50 perhaps due to wanting to be overcautious in this his opus magnus as regards the interpretation of experimental results. It will suffice for our purpose here to review Haller’s main conclusions about irritability, as they are presented in both the Elementa physiologiae and in the roughly contemporary third edition of his highly successful textbook on general physiology, the Primae lineae physiologiae (1767). In experimentally based Hallerian theory, every muscle is endowed with at least three kinds of forces: (1) a dead force (elasticity), (2) an active contractile power resident in its proper substance (vis insita), and (3) a power derived from the nerves and therefore from the soul. Irritability, therefore, has to be related to the first two physical or “natural” forces, which Haller found to be very different from each other. The dead force is that by which a fiber “resists lengthening out of its substance, and, when the extending power is taken away, restores the fibre to its former size.” This dead force is not exclusive to muscle, but is shared by a number of biological materials from both animal and vegetal origin, like feathers, flax, hairs, membranes, and vessels, as well as muscles following several days of having been excised from an animal.51 None of these materials would react to being just touched with a sharp or electrified point, as is immediately observed in fresh muscle due to the activation of its vis contractilis musculis insita. In comparison with the dead force, this vis insita or vis viva is “more proper to life,” since it may remain for several hours in an excised muscle. It is also “manifestly quicker” and capable of performing “the greatest motions” in response to pricking, stretching, or applying acrid substances to the muscle, “but most powerfully of all by a torrent of electrical matter.”52 The immediate explanation of contraction itself is based on the Boerhaavian model of a minimal fiber. Haller states clearly his position on this in the famous dictum that opens the Elementa physiologiae: “fiber is to the physiologist what line is to the geometrician.”53 Here he is alluding to a straight series of connected points as the fundamental unit of all polyhedral forms, which in material terms corresponds to a row of earthy particles sequentially joined to one another by a cohesive glue (see Fig. 12.1B). Contraction, therefore,

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Non-Spiritual Physiology II: seems to be a more brisk attraction of the elementary [earthy] parts of the fibre by which they mutually approach each other, and produce as it were little knots in the middle of the fibre. A stimulus excites and augments this attractive force, which is placed in the very nature of the moving fibre. The other explanations are hypotheses.54 Such other hypotheses are then summarily reviewed and discarded, starting from that one of intramuscular “nervous vesicles swelling by a quicker flux of nervous spirits” according to Boerhaave,55 for “they are inconsistent with anatomical truth, which demonstrates the least visible fibres to be (p.192) cylindrical, and in no part vesicular; and likewise repugnant to the celerity with which muscular motion is performed, and with the bulk of a muscle being rather diminished than 56

increased during its action.”

Thus Haller denied that animal spirit would swell anything within muscles, but stayed short of dismissing the animal spirit altogether, for this is mentioned immediately in the following paragraph as the cause that excites contraction (see quotation below). He evidently had trouble deciding what to make about the animal spirit, as he had it also accepting an electrical fluid moving within

Figure 12.8: Schematic illustration of Haller’s hypothesis of muscle fiber contraction. The constituent minimal fibers or fibrils consist of earthy particles aligned in a row, each particle connected to the two contiguous ones in the row by a glutinous substance. Shrinkage of this substance upon stimulation causes longitudinal approximation of the particles and therefore diminution in fibril length. (Illustration taken with permission from Frixione, 2000b, fig. 2.8, p. 45)

nerves.57 As to the agency that pulls the elementary particles of a muscle fiber closer to each other, so as to shorten the whole fiber, the textbook remains silent. Still, the Elementa physiologiae discusses again the only two options available from the chemical composition of muscle—earth and gluten (Fig. 12.8)—and comes to the same conclusion he had reached earlier in his milestone treatise on irritability (see above): it is in the second one where the dynamic capacity resides.58

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Non-Spiritual Physiology II: Impressive as they were, the scientific novelties presented by the Swiss experimentalist included conclusions that, coming from such a respected authority, might have been even more unsettling for his contemporaries than those thrown to them by the “preposterous” La Mettrie. For it was first the venerable Galen who decreed, following the Stoics and contrary to the wisdom he had inherited from his more brilliant elders in Athens, that plant life is totally soulless and the activities of internal organs in animals very much so too.59 Then Descartes had appeared suggesting that animal bodies, including those of humans, operate like automated machines. At about the same time, British physicians Harvey and Glisson seriously imagined that the blood and even simple fibers could have a primitive life of their own. Next Baglivi had dared to envision a physiological system in which fibers had the primacy. Now nearly everyone talked about “living fibers” acting by themselves, leading to the publication of openly heretical works like L’homme machine. Therefore, despite the efforts made by Stahl and his followers to counter this massive attack on religious fundamentals, it was only to be expected that sooner or later an outstanding scientist like Haller would allow himself to issue statements such as this: “The motive cause which occasions the influx of the animal spirits into the muscle so as to excite it into action, seems not to be the soul, but a law derived immediately from God.”60 The animal spirit—animae spiritus—managed by an impersonal law, or something other than the anima? Still worse, in the next paragraph Haller confirmed that, whatever divine law drives animal movement, its enforcement is purely corporeal: “It is so certain that motion is produced by the body alone, that we cannot even suspect any motion to arise from a spiritual cause, besides that which we see is occasioned by the will.”61 The situation had thus changed from granting that motion in certain parts of living organisms could perhaps take place without spiritual assistance, to claiming that only certain motions are spiritually guided in animal bodies, including that of man. The reactions to this atrocious position were immediate.

The vis nervosa Johann August Unzer (1727–1799; Fig. 12.9), a leading though moderate Stahlian who was established in northern Prussia, politely conceded that “The physiological works of Haller teach us, in a manner almost impossible to be surpassed, the mechanism of all parts of the animal body.” And next he adds: But do we know those laws by which the proper animal forces govern the body when acting separately from the physical and mechanical, and independently of them? Truly, no! or at least very imperfectly. The thoughts and desires are animal moving forces of the animal organism.62

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Non-Spiritual Physiology II: Unzer’s allegedly more complete picture of the problem distinguished between animal forces that act in accord with the sentient force of the mind, and animal forces that do not. Thoughts and desires belong obviously to the first type, in which case: “These united animal and sentient forces are termed animal sentient forces; and the movements they produce are sentient actions (actiones animae).” Now, the text continues, “When the animal forces act independently of the sentient force, they are termed pure animal forces or nerve forces [vis nervosa], and their movements are purely animal or nerve-actions.”63 In this context “irritability,” the word of the day, would denote a movement produced by a purely animal (i.e., mind-independent in this ambiguous nomenclature) force put into action by an appropriate stimulus, either natural or artificial. But Unzer also points out that muscles cannot be entirely freed from their nerves without damaging them, so that experiments become then unreliable. And since “all muscular movements which are attributed without adequate grounds to the irritability of muscles can also take place in virtue of impressions on their nerves,…it is probable that (p.193)

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Non-Spiritual Physiology II: no truth in all physiology is so physically certain as this; that all animal movements of muscles are primarily effected through the nerves only, whether in, or without connection with, the brain and the mind.”64

Haller’s results, in brief, were inconclusive and misleading to Unzer. As he saw it, muscle action is necessarily dependent upon the “pure animal forces.” The term corresponds evidently to the more common “animal spirit” as indicated by Unzer himself, although with a somewhat dubious choice of words (i.e., using vital instead of

Figure 12.10: Georg (Jiri) Prochaska (1749–1820), a Czech neurophysiologist who tried to explain the nerve impulse in the light of the new physiology, referring to it by the term vis nervosa (nerve force) instead of “animal spirit,” which it gradually replaced. He began to suspect that, rather than something that moves along within nerve fibers, the nerve force is rather a property of the fibers themselves. (Detail of line engraving; Wellcome Library, London, cat. V0004798)

animal as the adjective): Nerve-actions require the presence and free action of the vital spirits [lebensgeister in the original German text] in the animal machines…The cortical substance of the brain secretes the vital spirits from the blood, and distributes them to the nervous system. To this extent, the vital spirits and the brain can be considered as being necessary to the two kinds of vis nervosa [Nervenkraften in the original German text].65 Thus at least in nomenclature, if not in concept, “animal spirit” was beginning to be replaced by something else. This substitution went even further in the work of Unzer’s pupil Jiri (Georg) Prochaska (1749–1820; Fig. 12.10), a young Czech physiologist counted among the rising stars who might finally, and convincingly, remove the obscurities still surrounding nerve conduction.66

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Non-Spiritual Physiology II: In a 1784 dissertation on the functions of the nervous system, following a critical overview of the history of animal spirit, Prochaska undertook a detailed analysis of “What is understood by the vis nervosa, and what are its general properties.”67 Here he asserts that an invisible element enters into its composition, and that this constitutes the producing cause of all the functions of the nervous system. Since this is as mysterious and unknown as

Figure 12.9: Johann August Unzer (1727– 1799), a professor of medicine at the University of Halle like Stahl and Hoffmann before him, took issue at Haller’s physiology as simplistic and unreliable. While admitting the exceptional value of his Swiss colleague’s findings, he claimed that in the end they explain very little so far as the nervous system is concerned. Unzer chose to stay comfortably within the animistic outlook, proposing that nerve reflexes are the result of interplay between “animal sentient forces” and “sentient actions.” (Line engraving by unknown author; public domain picture, freely available by courtesy of H. P. Haack at

the vis attractiva of matter http://commons.wikimedia.org/w/ [conceived by Newton], it index.php? seems to me that it may be title=Special%3ASearch&search=Johann+August+Unzer& termed with (p.194) propriety the vis nervosa. I leave the inquiry, as to its nature, to the very sagacious and ingenious men already engaged in philosophical experiments. I shall only attempt to determine some of its general properties, before I enter upon the special functions of the nervous system.68 Interestingly, in Prochaska’s view of the active factor in nerves this is no longer just something contained within and capable of moving along them, but rather an intrinsic property that can be lighted up. In his words: “As the spark is latent in the steel or flint, and is not elicited, unless there be friction between the flint and steel, so the vis nervosa is latent.”69 Furthermore he intuited that, whatever the nature of the vis nervosa, it could not depend solely on the mere content of the nerves. Prochaska’s imagination was indeed fertile and unbounded:

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Non-Spiritual Physiology II: This property of the nerves does not depend solely on their medullary pulp, …but it appears…to be rather some other principle added to the medullary pulp, the conjunction of the two constituting the whole vis nervosa; and possibly the diligence of the very sagacious observers of nature may discover whether that principle be electricity, or phlogiston, or some species of air, or the matter of light, or a something compounded of these. That other principle, whatever it may be, seems to come to the nerves with the arterial blood, by means of the numerous blood vessels which accompany the nerves of the whole body throughout their whole course; or to be attracted from the air through inorganic pores; or in both these ways, and not to be sent into the nerves from the brain, as its only source, although the brain itself appears to acquire a suitable portion of the same principle through its own vessels.70 Still, the weight of a millennial tradition proved hard to dispel, for Prochaska also held that Another function of the nerves [apart from conducting sensations to the brain and motor commands to muscles] consists in a certain power over the blood-vessels, and specially the capillaries, in virtue of which, when the nerves are stimulated, they excite in that part to which they are distributed a much more copious accumulation of blood [or body fluids derived from the blood] than would have taken place in the normal condition of circulation. This phenomenon is termed congestion of the humours, afflux, derivation, abnormal direction, descent of the humours.71 A number of common physiological responses to various physical or purely mental stimuli bear witness to this effect of nervous excitation, he explains, from blushing to tear shedding, to salivation, to nipple and penis erection. And from this reasonable consideration he goes on to conclude that muscle contraction is just another instance of this general property: Since, therefore, irritation of the nerves causes congestion of humours in the vessels, it is easy to infer that in this same manner nerves, when irritated, excite the muscles to which they are distributed to contraction, that is to say, by the greater accumulation of the humour alone, caused in the vessels of the contracted muscle.72 Fluid injection, only this time being blood or humors instead of animal spirit, was once again seriously regarded as the more probable explanation of muscle contraction, just as in centuries of old. And thus Prochaska remained convinced that irritability is “necessarily dependent on the mechanism described” by him.

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Non-Spiritual Physiology II: Haller’s theory of irritability, on the other hand, was much better received and appreciated in southern Europe, particularly in Italy, where an enthusiastic Hallerian school quickly flourished at the University of Bologna under the lead of Leopoldo Marc’Antonio Caldani (1725–1813). Haller himself reported,73 quoting from a personal letter, how Caldani had been able to demonstrate twitching in muscles when an electrified rod was applied to their nerves, even after these had become almost dry and insensitive to stimulation with a needle. Probably still under the influence of Giorgio Baglivi,74 Caldani used these methods to test repeatedly, and to no avail, the irritability and sensibility of the dura mater. Some of these experiments were carried out in collaboration with the younger Felice Fontana (1730–1805), another admirer of Haller who, as we shall see next, took upon himself the concrete duty of expelling the animal spirit from physiology.

Animal Spirit Dismissed As it turned out, Fontana (Fig. 12.11) became one of the staunchest fighters for the cause of irritability, sometimes even disagreeing with his revered Haller over details of interpretation.75 Convinced that it constitutes a purely physical process that both Haller and his critics had occasionally compared with gravitation,76 and taking his inspiration from Newton’s approach to the study of motion in general, in 1767 Fontana established his ambitious Laws of Irritability. Right from the dedicatory page that serves as an introduction to this work, Fontana declares that his main objective is to get rid of, once and for all, the distracting animal spirit: I have noted that not a few important names and authorities openly deny this property of muscle fiber [irritability], although in such skepticism they overlook Haller’s experiments. Among the Hallerians as well no one up to now has shown that animal Spirits could not be the effecting cause of muscular movement. The reward of my effort on this problem has been to read the animal Spirits out of office, forever.77 (p.195)

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Non-Spiritual Physiology II: Following a detailed review and a critical analysis of the properties of irritability, based upon numerous experiments of his own, Fontana concludes: “From the above it flows forth spontaneously that the effective cause of muscular movements is most emphatically not to be ascribed to the animal spirits.”78 And next he continues with an urgent call to acknowledge this conclusion:

In order that the system of irritability may be validly established, the sum of matters stands on this, that from effecting causes of irritability the animal spirits be driven forth and revealed as an exciting cause. The too much neglected demonstration of this truth, even by the Hallerians themselves, brought it about that up to now the mechanists should attribute to nervous juice all the effects of muscular movements; in the truer view it should be accepted as depending on the new property of muscular fiber [irritability] which with marvelous ingenuity and sagacity the distinguished Haller suspected and with

Figure 12.11: Felice Fontana (1730– 1805), an Italian abbot, one of the most ardent “Hallerians” and a skilled experimenter, devised a set of Laws of Irritability and took upon himself the task of reading “the animal Spirits out of office, forever.” (Sculptured portrait at the Regio Museo di Storia Naturali et di Fisica, Florence; Wellcome Library, London, cat. M0018822)

the highest dexterity experimentally confirmed. Fontana’s wishful thinking clearly did not prosper, since the notion of animal spirit remained around for some time. Among other things, this was because Giambattista Beccaria (1716–1781), Tommaso Laghi (1709–1764), and other rivals of Caldani’s group had begun to associate animal spirit with the electric fluid within nerves and muscles.

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Non-Spiritual Physiology II: Later in his career Fontana himself eventually had to admit that “we are not only ignorant of muscular motion, but cannot even imagine any thing to explain it, and we shall apparently be driven to have to recourse to some other principle.”79 This last issue never happened because irritability was soon discovered to exist also in other cells apart from muscle fibers, a phenomenon that would be further studied during the 19th century,80 thus becoming a standard concept in biology that survived well beyond the 18th century, albeit in disguise under a different terminology.81

Concluding Remarks Haller’s work on irritability and its immediate aftermath, especially among the Italians, marked the onset of irreversible decline for the time-honored idea of animal spirit. The increasing suspicions about the existence of animal spirit, in turn, threw a dissolutive shadow of doubt regarding the presence of “vital or natural spirit” in the blood, something about which everyone from Galen onwards had no or comparatively few reservations. Thus an almost audible crack, under the weight of mounting experimental evidence, finally announced the imminent collapse of a scientific tradition that, like few others, had weathered over two millennia. And it was mainly Haller, with his unprecedented huge load of experimental work, who in fact marshaled the birth of a thoroughly spiritless or rather despirited physiology. The two main conceptions called to substitute for the crumbling edifice—irritability and electricity—were both quite mysterious and difficult to grasp or enter into the standard explanatory categories, but they had the unmistakable fragrance of something excitingly new. Notes:

(1) Boerhaave, 1742–1746, vol. 2, §288, note 1, pp. 316–317. (2) Ibid., vol. 1, §39 and 40, pp. 80–81. (3) Ibid., §41, p. 85. (4) Ibid., note 6, p. 87. (5) To what extent Boerhaave just abandoned his iatrophysical credo in this critical matter, or rather evolved to a more cautious intellectual position as a result of his Calvinist beliefs, is controversial. For discussions of these interpretations see, respectively, Cook, 2000, and Knoeff, 2002, esp. pp. 195ff. Another view can be found in Steinke, 2005, pp. 26–34. (6) Boerhaave, 1731; quoted in Knoeff, 2002, p. 195. (7) Boerhaave, 1742–1746, vol. 2, §187, p. 71. (8) Boerhaave, 1735-1737; quoted in Steinke, 2005, p. 34. Page 27 of 31

Non-Spiritual Physiology II: (9) Boerhaave, 1735, Part II, p. 46. Atomism, a materialistic philosophical school originated in Greek antiquity with Leucippus and Democritus, then continued into the Hellenistic period with Epicurus and Lucretius (see Chapter 1), was rescued from oblivion like other aspects of ancient science, and put again in circulation in the early 17th century by Pierre Gassend (or Gassendi, 1592–1665) and others (see Lennon, 1991). (10) Ibid., p. 52. (11) Boerhaave, 1737, §21, pp. 4–5. See also Rather, 1969, and Lindeboom, 1970. (12) Swieten (English translation), 1744, vol. I, Sect. 38, pp. 98–99. See also ibid. Sect. 21, pp. 39–40. (13) Gorter, 1731, pp. 1–5, and Plate I. See also Rather, 1969. (14) Gorter, 1737. (15) See Chapter 11. (16) See Chapter 1. (17) Iatrophysics or iatromechanics; that is, the 17th-century medical school in which, under the influence of Descartes, all physiological phenomena were explained in terms of simple mechanics, and therefore spontaneous motion was considered impossible (see Chapter 8). (18) Boerhaave, 1730-1735 (1959); cited in Steinke, 2005, p. 33. (19) See Rather, 1965, pp. 61–62. (20) Kaau-Boerhaave, 1745. (21) Gaubius, 1778, §188, p. 51. (22) Swammerdam’s work in this context is reviewed in Chapter 7. (23) Gaubius, 1778, §137, p. 37, and §142, p. 39. (24) Ibid., §143, p. 39. (25) Ibid., §188–189, p. 51. (26) Ibid., §190. (27) Gaub, 1747, Sermo academicus de regimine mentis quod medicorum est, §38; see annotated translation in Rather, 1965, p. 64. (28) Ibid., §39; ibid. Page 28 of 31

Non-Spiritual Physiology II: (29) Ibid., §41; ibid. p. 65. (30) See Chapter 11. (31) For various perspectives of this extraordinary figure in an extraordinary century see Vartanian, 1960; Wellman, 1992; Smith, 2002. (32) La Mettrie, 1747 (Jackson, 2004, pp. 71–72; translated here from the French original). (33) Ibid. (Ibid., p. 75). (34) Gaub, 1763, Sermo academicus alter de regimine mentis, §1; see annotated translation in Rather, 1965, p. 115. The epithets “Mimus” and “Momus” are not clarified in the translation, but they are obviously used here to ridicule La Mettrie and may be derived from the Latin mimus (mime), then intentionally corrupted to “momus” so as to reflect what Gaub felt La Mettrie had done with his scientific ideas. (35) For a study of Whytt’s career see French, 1969. (36) Whytt, 1751/1768, p. 128. Emphasized words as in the original. (37) Ibid., p. 148. (38) Ibid., p. 207. (39) For a compact biographical profile of Haller and links to relevant bibliography see Frixione, 2006. (40) Haller, 1755, p. 3 (p. 8 in Temkin, 1936 ed.). (41) Some historians have concluded that Haller’s most consequential contribution to physiology lies not so much in his many important discoveries, but in his method of doing science: abundance of hard facts obtained through tireless and well-designed experimentation, coupled to a minimum of cautious hypothesizing. For in-depth analyses of the Hallerian approach see Monti, 1990, and Steinke, 2005. (42) Haller, 1755, p. 4 (p. 9 in Temkin, 1936 edition). (43) For an account of this episode see Saussurre, 1949. (44) Haller, 1755, p. 38 (p. 28 in Temkin, 1936 ed.). (45) Ibid., p. 60 (p. 42 in Temkin, 1936 ed.); see also ibid., p. 58 (p. 40 in Temkin, 1936 ed.). (46) Whytt, 1755/1768, p. 293. Page 29 of 31

Non-Spiritual Physiology II: (47) Ibid., p. 292. (48) For a detailed analysis see Frixione, 2007. (49) Haller, 1762, Book 11, Section II, esp. pp. 440–466. (50) See Steinke, 2005, pp. 109–116. (51) Haller, 1767/1786, vol. I, Ch. 12, §391–393, pp. 226–227; Haller, 1762, Book 11, Section 2, §1–3, pp. 440–445. (52) Ibid., §400, pp. 231–232; ibid., §4–6, pp. 446–451. (53) Haller, 1757, Book 1, Section 1, pp. 2–8; see also Haller, 1767/1786, vol. I, Ch. 1, §1–7, p. 9–11. (54) Haller, 1767/1786, vol. I, Ch. 12, §407, p. 236. (55) See Chapter 10. (56) Haller, 1767/1786, vol. I, Ch. 12, §407, p. 236. (57) See Chapters 14 and 15. (58) Haller, 1762, Book 11, Section 2, §12, pp. 464–466; cf. note 45 above. (59) See Chapter 11 for these and the following precedents. (60) Haller, 1767/1786, vol. I, Ch. 12, §408, p. 237. (61) Ibid., §409, p. 238. (62) Unzer, 1771, Preface (Laycock, 1851, p. 4). (63) Ibid., §6 (ibid., pp. 14–15). Emphasized words and round or square brackets as in the English translation. “Nerve forces,” a word printed in singular (Nervenkraft) in this paragraph of the original German text, is found in this translation rendered as a plural and parenthetically equated with vis nervosa, a Latin expression used also by Haller though not by Unzer. (64) Ibid., §388, pp. 211–212. Emphasis as in the original. (65) Ibid., §362, p. 195. Notes within square brackets added here, Latin words italicized as in the original. (66) For a brief contemporary evaluation of the problem see H. A. Wrisberg’s note 105 in Haller, 1767/1786, vol. I, pp. 221–222. (67) Prochaska, 1784, ch. II, sect. 3 (Laycock, p. 389).

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Non-Spiritual Physiology II: (68) Ibid. (Ibid., p. 390). Emphasis as in the original. Note within brackets added here. (69) Ibid. (Ibid.) Emphasis as in the original. (70) Ibid., ch. III, sect. 1 (Ibid, p. 407). Emphasis as in the original. (71) Ibid., sect. 2 (Ibid, p. 408). Notes within brackets added here. (72) Ibid., sect. 3 (Ibid, p. 413). He had first suggested this neo-“balloonist” hypothesis of muscle contraction a few years earlier (Prochaska, 1778). (73) Haller, 1756-1760, vol. 3, pp. 143–144. (74) See Chapter 11. (75) For a study on Fontana and his work see Knoefel, 1984. (76) See above in this chapter and Frixione, 2007. (77) Fontana, 1767, dedication page; see English translation in Marchand and Hoff, 1955, p. 304. (78) Ibid., Part II, §6 and 7, p. 326. (79) Fontana, 1787, pp. 283–284. (80) See Verworn, 1913. (81) See Fulton, 1926; Needham, 1971.

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Introduction

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.199) Introduction In the previous section of this book, we showed how natural philosophers of the late-17th and early-18th century began to search for alternative ways to account for how the nerves and muscles might function, starting a break away from older animal spirit ideas. Haller’s admission that he could not imagine what might be happening within the nerves or muscles was reflective of the demand for finer tools, more information, and better concepts. He tried to construct his nerve and muscle physiology from a more empirical basis (nerves are sensitive, whereas muscles are irritable), even though he could not completely abandon elements of the animal spirit doctrine. The same can be said about Newton and Hartley in their quests to try to think of nerve physiology in a new way, one based on vibrations of particulate matter. Indeed, physicians, physicists, and others involved in what we would now call the life sciences were increasingly recognizing flaws, and in some cases quite serious cracks, in the animal spirit edifice that had been built and then altered or repaired over the ages. But without a good alternative to turn to, one that would go hand in hand with better technologies and methodologies, there was no mass exodus during the first half of the 18th century from very speculative theories to an explanation of nerve conduction (and muscle contraction) more firmly rooted in hard experimental facts. As we shall see in the three chapters in this section, however, the questioning that was occurring in the first half of the 18th century did have significant consequences. Like some of the experimental findings that began to appear late in the 17th century, what was transpiring forced people to think more deeply about the fundamental nature of the nerve fluid. In effect, natural philosophers were now pondering the sanctity of the ideas that many individuals had accepted rather uncritically, increasingly opening the door wider for a better alternative to explain motor and sensory, and even higher-order, phenomena. Page 1 of 7

Introduction In this regard, Newton’s thinking was particularly important, and for several reasons. First, he raised the possibility that the nerve force might be invisible, drawing attention away from a viscous fluid that could somehow stimulate the muscles—muscles that Glisson and others had by this time demonstrated did not inflate and expand like balloons. Second, he emphasized that such a force must be able to account for the incredibly fast speed of nerve conduction, something a secreted liquid seemed to fall short of doing. Third, Newton had made it absolutely clear that whatever the force is thought to be, it must still obey the laws of physics. And fourth, Newton was important because many natural philosophers following his large footsteps were convinced that the mysterious force must in some way involve particles in motion. As the second half of the 18th century got underway, a viable alternative to more traditional notions about the animal spirit slowly began to come to the fore. Whereas Newton and Hartley had been thinking about vibrations that might have an elastic or electrical virtue, some natural philosophers began to entertain the idea that the nerves might work by, of all things, electricity itself. To say the least, this idea seemed like both a good one and also a very bad one when it began to surface at this pivotal moment in time. On the one hand, electricity did seem to be a very rapid force, one capable of almost instantaneously bringing sensory information to consciousness, quickly stimulating muscles to contract, and explaining a myriad of experimental findings. Moreover, it was a force that could be studied in natural settings, and even more effectively in the laboratory with frictional machines, Leyden (storage) jars, and good experiments. But on the other, it was hard to imagine where such a force could come from, and even harder to envision why it would not electrocute or in some other way act deleteriously on the moist body possessing it. These were serious objections that would take time to overcome, and not seeing how the electricity could be confined to the nerves or perhaps the nerves and the muscles, Haller, among others of great stature, would at least initially have great difficulty with it. Chronologically, there would be considerable experimental evidence for at least some living animals releasing electricity before these perplexing matters could be understood.

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Introduction To appreciate what will now transpire, we shall begin with a chapter on how the science of electricity was blossoming during the middle of the 18th century, providing the contextual backdrop for the emerging concept of animal electricity. We shall then show how three types of electric fishes revealed that some animals probably do possess electricity, or a force that then seemed very closely related to frictional and atmospheric electricity. And finally, we shall conclude this section with a chapter showing how what was learned from torpedo rays, the so-called electric “eel,” and electric catfishes was then expanded to animals that do not have electric organs like these fishes and do not shock, and with further experimentation and a better understanding of chemistry and membranes, how the force was determined to be the same as manmade or atmospheric electricity. Thus, these chapters will focus on the conceptual and experimental origins of the electrical force that would prove to be the long-awaited successor to more speculative ideas about the identity of the spirit associated with the muscles and nerves. Importantly, the historical record will show that the shift that took researchers away from the structure (p.200) of the animal spirit doctrine—with the spirit originating in the brain and coursing through the hollow (or more solid) nerves to activate the muscles—was less than instantaneous. There would be considerable resistance to this paradigmatic change, and too great a need for more information for those scientists (most importantly, Luigi Galvani) now thinking about more than just a few unusual fishes to abandon the structure of the old model as the 18th century was drawing to a close. The idea that the electricity might originate from the nerves and muscles themselves, as we shall see, would be a 19th-century development. Moreover, understanding just how the nerves and muscles might do this will take us well into the 20th century. With these thoughts in mind, let us now see how new observations and experiments, better research tools, discoveries made far from the shores of Europe and in Europe itself, and a new leadership affiliated with national scientific societies and great universities converged to create a new way of thinking—one in which even our neuromuscular physiology would be presented as electrochemical in nature.

(p.201) Chronology Science

Cultural Context

1600 Gilbert’s De magnete

(See chronology in previous section) |

1671 Redi associates falciform muscles with | torpedo’s numbing power

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Introduction

Science

Cultural Context

1678 Lorenizini’s book on torpedoes 1709 Hawksbee’s rotating globe and frictional electricity experiments

|

1743 Krüger calls for electrical medicine

|

1746 Van Musschenbroek invents Leyden jar 1750 Ingram uses “electric energy” to describe eel’s discharge

|

1751 Franklin’s Experiments and Observations on Electricity

|

1751–72 Diderot’s and d’Alembert’s Encyclopédie 1753 Canton’s pith ball electrometer 1756 Van 's Gravesande compares electric eel to Leyden jar 1769 Bancroft’s book on Guiana (eel electricity) 1772 Walsh’s torpedo experiments 1773–75 Hunter describes torpedo and eel electrical organs 1774 Priestley discovers oxygen 1774 Cullen: First Lines of the Practice of Physic 1776 Walsh observes an eel spark in darkness

American War of Independence

Cavendish’s model of the Torpedo

Adam Smith: Wealth of Nations Watt’s commercial steam engine 1781 Kant: Critique of Pure Reason

1784 Mesmer’s theory of animal magnetism discredited 1789 Lavoisier: Traité élémentaire de chimie Page 4 of 7

French Revolution starts (storming of Bastille)

Introduction

Science

Cultural Context

1791 Galvani: De viribus electricitatis

Mozart dies at age 36

1794 Galvani: Trattato dell’Arco Conduttore Erasmus Darwin: Zoonomia 1800 Volta’s battery 1802 Treviranus coins the term “biology”

1802 Paley: Natural Theology 1808 Beethoven: 5th Symphony

1811 Bell: A New Anatomy of the Brain 1818 Mary Shelley: Frankenstein 1819 Schopenhauer: World as Will and Idea 1822 Magendie: motor and sensory neurons 1824 Beethoven: 9th Symphony 1825 Nobili invents galvanometer 1827 Ohm enunciates “Ohm’s law” 1828 Nobili demonstrates “frog currents” 1828 Wöhler synthesizes urea and thus founds organic chemistry 1832–38 Davy and Linari provide more evidence for torpedo electricity 1833 Müller: Handbuch der Physiologie des Menschen 1839 Schwann: cell theory Faraday: Experimental Researches on Electricity (1839–55) 1844 Matteucci: Traité des phénomènes electro-physiologiques 1848 Du Bois-Reymond: Untersuchungen über thierische Elektricität 1849 Helmholtz calculates speed of nerve conduction

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Morse demonstrates telegraph

Introduction

Science

Cultural Context

1856 Helmholtz: Physiological Optics 1859 Darwin: Origin of Species

Dickens: A Tale of Two Cities

1863 Huxley: Man’s Place in Nature 1865 Transatlantic cable completed 1866 Mendel inaugurates genetics

Dostoyevsky: Crime and Punishment

1868 Bernstein measures negative variation 1869 Tolstoy: War and Peace 1871 Darwin: Descent of Man 1873 Clerk-Maxwell: Treatise on Electricity and Magnetism 1875 Caton begins experiments on electrical responses in the brain 1879 Edison’s incandescent light bulb 1874 First Impressionist exhibition in Paris 1897 Michelson-Morley experiment 1900 Rediscovery of Mendel’s work Planck begins quantum mechanics 1901 First Nobel Prizes 1902 Bernstein: membrane theory Overton: structure of membranes 1903 Wright brothers’ powered airplane flight 1905 Einstein: special relativity 1906 Golgi and Cajal share Nobel Prize for work on the structure of the nervous system 1907 Picasso: Les Demoiselles d’Avignon 1909 Blériot flies the English Channel

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Introduction

Science

Cultural Context 1914 Start of World War I

1915 Einstein: general relativity 1917 Lenin in St. Petersburg: revolution in Russia 1918 End of World War 1 1922 Eliot: The Waste Land 1936 J. Z. Young: squid giant axon 1937 Turing’s computational machine 1939 Hodgkin, Huxley: action potentials in squid giant axon

Start of World War II

1940 Cole, Curtis: action potentials in squid giant axon 1945 Atomic bombs dropped on Japan End of World War II 1949 Cole: electrical characteristics of squid giant axon 1952 Hodgkin, Huxley, Katz: nerve biophysics 1953 Watson, Crick: DNA (p.202)

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The Increasingly Electrical World

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

The Increasingly Electrical World C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0013

Abstract and Keywords This chapter studies the early history of electricity and explains how it helped prepare the electric fish experiments that showed that some living organisms can generate and release electricity. This became a landmark development that opened more minds to the possibility that humans function electrically. It shows how electricity became one of the most stimulating branches of experimental natural philosophy during the middle of the 18th century. It then connects this development to new technologies and events. This chapter also discusses Benjamin Franklin and his introduction to electricity, plant electricity, medical electricity, atmospheric electricity, and the obsession with invisible forces. Keywords:   electric fish experiments, experimental natural philosophy, electricity, Benjamin Franklin, plant electricity, medical electricity, atmospheric electricity, invisible forces

From a thousand Experiments it appears that there is a fluid far more subtle than Air, which is everywhere diffused through all Space, which surrounds the Earth and pervades every Part of it. And such is the extreme Fineness, Velocity, and Expansiveness of this active Principle, that all other Matter seems to be only the Body, and this the Soul of the Universe…. Reverend John Wesley (1760, p. 9)

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The Increasingly Electrical World As we have noted, the concept of animal spirit, which began with notions about vapors and then fluids coursing through hollow nerves, would grudgingly give way to the idea that the nerves and muscles function electrically. This development would begin to take place at the middle of the 18th century, with electric fishes—and not frogs—being the first star performers in the physiological drama that would now play out. As can be imagined, this change in thinking was based on some very important developments and new ways of viewing the natural world. One was a better appreciation of electricity as a fundamental force of nature, a force that might be capable of accounting for a wide range of physical phenomena, and perhaps even life phenomena. A second development, closely related to the first, was a willingness to envision nerve and muscle physiology in new ways. Exemplified by the advent of vibration theories, this new openness stemmed in part from the fact that earlier animal spirit ideas could not explain certain findings and observations, including what seemed like the instantaneous speed of nerve conduction. Yet another development worthy of note was the accumulating evidence, albeit indirect at first, suggesting that some of God’s creatures actually seem to function electrically. In this chapter, we shall look at the early history of electricity and how it helped to set the stage for the electric fish experiments that would show that some living organisms can, in fact, generate and release electricity—a landmark development that would open more minds to the possibility that even we might function electrically (although our electricity would, of course, be considerably more subtle and therefore harder to detect). In effect, this chapter will be devoted to how electricity rose to become one of the most exciting branches of experimental natural philosophy in the middle of the 18th century. We shall tie this development to new technologies and to events that would entertain and amaze scientists, kings, and even an inquisitive Philadelphia printer destined to emerge as a central figure in this remarkable drama.

Technology and the Science of Electricity The modern history of electricity started with William Gilbert (1544–1603), an English natural philosopher, who would later serve Queen Elizabeth I (1533– 1603) as her physician (Fig. 13.1). In 1600, Gilbert published a book dealing with the earth as a magnet, his De magnete, in which he tried to separate electricity from magnetism by “trustworthy experiments.”1 On the pages of this text, which was written in Latin, we encounter the word electricam, a term derived from the Greek word for amber (elektron), the fossil plant sap known since ancient times for its ability to attract straw and feathers when rubbed. Gilbert’s Latin word lives on today in various modern forms, as exemplified by terms “electricity,” “electric,” “electrical,” and “electrician,” but more importantly, his book stimulated interest in a plethora of electrical phenomena, and with that interest, both technological advances and new experiments. Page 2 of 38

The Increasingly Electrical World Machines that could create sparks by friction began to be produced in Germany during the second half of the 17th century.2 Otto von Guericke (1602–1686) of Magdeburg, who read Gilbert’s book, wrote about a sulfur globe “the size of a child’s head,” which had an iron shaft through its center that allowed it to be turned (Fig. 13.2). While the globe was rotating, a person could rub it with his hands, a piece of leather, or perhaps some wool.3 In 1672, Guericke wrote that a properly charged sulfur globe could repel suspended threads and feathers. Further, these actions could be accompanied by crackling sounds and sparks. Within a few decades, rotating glass cylinders and disks became the methodology of choice, as these frictional machines, having a higher surface-tovolume ratio, worked at least as well and could be more easily and economically (p.204) manufactured to specifications. Francis Hawksbee (1666–1713), who worked with various glass globes and cylinders, found that by rotating and rubbing his glass instruments, he could make them glow bright enough for him to read with their light (Fig. 13.3).4 In his book of 1709, he reported that charged glass vessels could also generate sparks, make a second glass vessel glow, and cause strings and thin pieces of leaf brass to dance. The movements of his suspended threads could even be used to estimate the “degree of electricity.”

Recognizing the importance of being able to detect and even measure electricity, John Canton (1718–1772) described and illustrated a better electrometer at mid-century.5 His device used suspended elder pith balls (Fig. 13.4). The

Figure 13.1: William Gilbert (1544– 1603), who wrote about electricity and magnetism in his De magnete of 1600.

pith ball electrometer quickly became a standard piece of equipment for natural philosophers engaging in the study of electricity.

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The Increasingly Electrical World Prior to Canton’s invention, but upon learning of Hawksbee’s achievements, Stephen Gray (1666–1736), who had been a silk dyer in Canterbury before moving to London, showed that electricity from glass could be transmitted over relatively long distances using threads and wires.6 In addition, Gray distinguished between materials that could conduct electricity (conductors) and those that could not (non-conductors), but that could serve as insulators. These developments, which were described in 1731, helped Gray to achieve some fame among experimental natural philosophers. Nevertheless, most people knew him far better for being the man who showed that the human body could be electrified and could even throw off perceptible sparks. In his most famous experiment, which would become standard fare in his own electrical shows and those of others, Gray suspended a charity school boy in his care in a horizontal position using silk cords hanging down from a ceiling (Fig. 13.5). After being “electricised” with a glass cylinder held near his feet, the schoolboy was able to attract feathers and pieces of brass to his body. Even more astonishing, visible sparks accompanied by crackling sounds could be drawn from his charged body without hurting him in the least. Although machines for generating electricity more efficiently continued to be developed, there was still no way to store the electricity at this time. Being able to package the generated electricity in varying amounts, and then having the ability to release it on command, would play an extremely important role in our animal spirit story. Among other things, the advent of Leyden jar would provide a model for how many natural things, from thunder and lightning to biological phenomena, might work. Notably, releasing stored electricity on demand would allow researchers to compare the discharges of a few unusual fishes to a device releasing “true” electricity. The fact that similar sensations could be produced from living creatures and a properly charged Leyden jar would become one of the first pieces of replicable evidence to suggest that some living organisms just might be electrical—an idea that challenged the imagination and must have seemed incredible at the time, because the creatures that initially seemed most likely to be electrical felt slimy and lived in watery habitats. The much-needed Leyden (or Leiden) jar for storing electricity is basically a glass vessel that is covered with metal foil and filled with water, lead shot, or another conductor of electricity (Fig. 13.6). Thus, its basis is an inner and an outer conductor of electricity separated by a non-conductor, namely the glass. Attaching the jar to a metal rod called a “prime conductor,” which in turn is connected to a frictional machine, allows it to be charged. To release the accumulated charge, one merely completes the circuit between the inside and the outside of the charged bottle, and this could be done through metal wires, people holding hands, or any other conductor or conductors of electricity.

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The Increasingly Electrical World The Leyden jar received its name because Pieter van Musschenbroek (1692– 1761), a professor of mathematics and physics at the University of Leiden in the Netherlands, was involved with its accidental discovery in 1746 (Fig. 13.7).7 Jean Nicolas Sébastien Allamand (1731–1787), another Leiden physicist (who would later publish evidence showing that its discharges can be like those of a South American “eel”), and Andreas Cunaeus (1712–1788), a visiting student, had been working with him when the accidental discovery took place. (p.205)

Figure 13.2: Otto von Guericke’s 1672 illustration of a large sulfur globe being used in an electrical experiment.

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The Increasingly Electrical World Van Musschenbroek described his “terrible experiment, that I will advise you not to try personally nor will I do again, not even for the entire Kingdom of France” in a letter written in French to his contact at the Académie des Sciences in Paris (he was a foreign member). In translation, he continues:

I was doing some research in order to reveal the forces of electricity. To that purpose, an iron bar had been suspended with two threads of blue silk, and a glass globe that was spun rapidly had been placed near one of the extremities. It had been rubbed with the hands and communicated its electric force freely to the iron bar. On the other end, a brass wire hung freely. With my right hand, I was holding a round glass vase partly filled Figure 13.3: A frictional machine for with water. With my left producing electricity from glass. This hand, I was trying to draw illustration comes from Francis the crackling sparks that Hawksbee’s book, Physico-Mechanical issued from the electrified Experiments on Various Subjects, dated iron bar toward my finger. 1709. Suddenly, my right hand was hit with so much commotion that my body was rattled as if struck by a thunderbolt. My limb and entire body were terribly affected in a way that I cannot express.8 Ewald Georg von Kleist (1715–1759) from Kammin, a town in Pomerania (now Poland), who had been a student at Leiden, had actually come forth with a comparable device in 1745. His instrument used a water-filled, glass medicine bottle with a nail protruding through its cork stopper, which had been connected to an electrostatic machine. When Kleist held the outside of the bottle and touched the nail, he discharged the electricity through his body, also quite by accident. Nevertheless, what Kleist had also achieved is often forgotten today. This is because van Musschenbroek was an internationally known physicist and Leiden was a bustling (p.206) Page 6 of 38

The Increasingly Electrical World center of scientific activity, and also because of how the jar was introduced before the French Académie and the name it was to be given.

The more important point for our story is not that Kleist Figure 13.4: John Canton’s 1754 preceded van Musschenbroek, illustration of his pith ball apparatus for who then became better known. detecting electricity. Rather, it is that natural philosophers finally had various machines for making electricity, devices for detecting it, and ways of storing it by the middle of the 18th century. And with their growing armamentariums, they went before local and national scientific societies, elsewhere in Europe, and even across oceans, talking about and demonstrating the newly discovered wonders of electricity. These shows, as can be imagined, generated even more interest in electrical phenomena, and this stimulated even more questions about its role in nature. Not to be overlooked, although Sir Isaac Newton had died in 1727, his influence had not diminished, especially when it came to studying and understanding the pervasiveness of nature’s invisible forces, which was how electricity began to be seen as people looked more carefully at many facets of the natural world (see Chapter 9 and below).

Science and Amusements Natural philosophers interested in exploring the wonders of electricity, physicians who thought there might be merit in applying small amounts of electricity at the bedside, and showmen hoping to awe audiences began to acquire electrical instruments, fostering what would become a real growth industry in the mid-18th century. Of course, the aforementioned divisions were not really distinct, since anyone could call himself a natural philosopher and, at least in the British North American colonies, a physician. Further, leading statesponsored physicists, and not just itinerant showmen hoping to scratch out a living, directed some of the most spectacular demonstrations, albeit not so much for the scruffy masses able to pay a few small coins to be entertained, but for royal onlookers and their sometimes erudite entourages.

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The Increasingly Electrical World Abbé Jean-Antoine Nollet (1700–1770) was a leading figure in the nascent science of electricity, writing important works on the subject9 and serving as the official court electrician to Louis XV (1710–1774) and as an influential member of the French Académie des Sciences (Fig. 13.8).10 He was, in fact, van Musschenbroek’s correspondent at the French Académie and the scientist who coined the term “Leyden jar” when informed of the Dutch physicist’s discovery. Highly regarded at home and abroad, he came forth with a new theory of electricity and published a course on experimental physics that dealt with the laws of electricity. Nollet also understood the importance of being a good showman, and some of his demonstrations were indeed memorable. In one, conducted at Versailles, where the royal family resided and considerable governmental business was transacted, he asked 180 grenadiers to hold hands. When the soldiers at the ends of the human chain completed the circuit to some charged Leyden jars, all leaped involuntarily to the explosive discharge. The spectacles delighted (p.207)

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The Increasingly Electrical World Nollet’s benefactor, the King, as well as aristocrats from the Ancien Régime, family members, and others in attendance. In fact, Louis XV was so impressed that it is said that he asked Nollet to repeat what he had done, but this time in Paris.

Being Abbot of the Grand Convent of the Carthusians, Nollet now utilized 200 monks from a monastery in an even more dazzling demonstration. Connected by 25-foot pieces of iron wire, the monks in his order formed a chain over a mile long. They “gave a sudden spring” into the air when the

Figure 13.6: An assortment of Leyden jars for storing electricity. This figure is taken from Benjamin Franklin’s pamphlet on electricity, first published in 1751.

circuit they were forming was connected to a “battery”

1746).

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Figure 13.5: Stephen Gray’s suspended boy experiment, showing how sparks could be drawn from the boy’s nose by bringing a finger close to it (from Nollet,

The Increasingly Electrical World (p.208) of Leyden jars wired together.11 As for their accompanying utterances, some of the pious fathers even seemed to swear! Nollet wrote: “It is interesting to see the multitude of different gestures, and to hear the instantaneous exclamation of

Figure 13.7: Pieter (Petrus) van Musschenbroek (1692–1761), the gifted Dutch physicist who was involved with the accidental invention of the Leyden jar.

those surprised by the shock.”12

Needless to say, most shows were far from this spectacular, although the lectures and demonstrations were still billed as entertaining.13 This was, after all, the era of the electrically charged suspended boy, of making one’s hair stand up, the “electrical kiss,” “electrical stars,” and “electrical rain.” It was also when audiences paid to see strong men buckle and even large farm animals knocked down with Leyden jar discharges. For additional amusement, they might even watch a glass of brandy set aflame when brought to the lips Figure 13.8: Jean-Antoine (Abbé) Nollet of an electrically charged (1700–1770), French physicist and person, or even their own lips, electrician. should they be bold enough to volunteer for the experiment. As put by social historian Simon Schaffer: “Electrical fire dominated London natural philosophy in the mideighteenth century” and “Public interest in the new electrical demonstrations was intense.”14

Benjamin Franklin’s Introduction to Electricity Benjamin Franklin’s (1706–1790; Fig. 13.9) introduction to electricity started with a lecture-show given by an itine

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The Increasingly Electrical World rant Scottish electricianentertainer. Yet his roots were humble.15 He was born in the opening decade of the century into a working-class family in Boston, where his father eked out a living making soaps and candles. With many siblings and little money available for his education, the boy who loved books had only a few years of formal schooling before being forced to enter a trade when he was only 9 years old. After finding his father’s candle-making business not to his liking, he was apprenticed to one of his brothers, who ran a printing shop and was critical of the powerful Congregational Church and the conservative Boston Figure 13.9: Benjamin Franklin (1706– establishment. With his brother constantly in trouble, as well as 1790), whose experiments in colonial perceived as abusive and Philadelphia led to a better appreciation unwilling to recognize his talents, of the nature of electricity. Franklin was Franklin ran away when the instrumental in transforming the wonders opportunity presented itself in of electricity into a hard science, and he 1723. After a brief stop in New drew attention to the pervasiveness of York, he made his way to Boston, this natural force. where he found employment as a printer’s helper. He was soon able to start his own printing business, and with his highly successful Poor Richard’s Almanack and The Pennsylvania Gazette, eventually built a printing empire and amassed a very large sum of money for an American tradesman.

During his time in Philadelphia, Franklin did many things to better himself and his community, one of the most significant of which was to help establish the American Philosophical Society for promoting the sciences in the colonies. He also took on a number of governmental posts, including Postmaster of Philadelphia in 1737. While on a trip to Boston in 1743, which combined postal business with seeing his family, he noticed an advertisement in the Boston Globe for a “Course of Experimental Philosophy” to be given by a Dr. Spencer (fl. 1740s) of Edinburgh.16 Being inquisitive, he paid to see the suspended boy demonstration and many other things, and to hear Spencer discuss such phenomena, which the Scot related to fire.

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The Increasingly Electrical World Franklin was so amused and amazed by his time with Spencer that he encouraged him to head south to Philadelphia for more showings. Franklin then advertised his shows and also served as his ticket agent. In some notes dated May 29, 1744, which were penned by a person who attended the show, we read: “Between the hours of 3 & 4 the Governor, Commissioners, and the rest of the Company went to hear a Philosophical Lecture on the Eye, &c. by A: Spencer, M:D:, in which he…proceeded to show that Fire is Diffus’d (p.209) through all Space, and may be produced from all Bodies, Sparks of Fire Emitted from the Face and Hands of a Boy Suspended Horizontally, by only rubbing a Glass Tube at his Feet.”17 Franklin was clearly taken by what he had seen and learned in Boston and now in Philadelphia. Within a short time, he would be buying all of Spencer’s electrical equipment and would be coming forth with new electrical experiments and insights.18

Electricity in the Heavens Two years after meeting Spencer in Boston, Franklin’s Library Company received a package of electrical equipment along with an informative Gentleman’s Magazine article on electricity.19 This was a gift from Peter Collinson (1694–1768), a natural philosopher and an agent for Franklin’s Library Company in London.20 It was now that Franklin started his own electrical experiments, writing to Collinson in 1747 that he had never previously “engaged in any study that so totally engrossed my attention and my time as this has lately done.”21 His experiments soon took up so much of his time that he left the dayto-day management of his lucrative printing business to a partner,22 wishing to pursue his science in a manner befitting a proper gentleman, knowing he had sufficient income and investments to do so. Franklin conducted his experiments with several other Philadelphia tradesmen. Early on, one of them, Thomas Hopkinson (1709–1751), discovered that points are far better than balls or “blunts” for releasing and attracting “the electrical fire.” This discovery led Franklin to the pointed lightning rod, a home-, workplace-, and life-saving tool that he gifted to humanity, and one that immediately made him world-famous as a natural philosopher and inventor.23 Franklin also began to question Charles François de Cisternay du Fay’s (1698– 1739) idea that there are two distinct types of electricity, vitreous and resinous.24 Du Fay’s thinking stemmed from the observation that stroking glass and amber seemed to have opposite effects (attraction vs. repulsion). He also questioned Nollet’s notions of two distinct electrical streams (affluent and effluent) traveling in opposite directions, drawing angry responses from Nollet in France.

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The Increasingly Electrical World Franklin now came forth with a very different thought, one that he developed in the 1750s. It was that an object will be “plus,” or “electricised positively,” if it has an “over quantity” or excess of electrical matter, and that it will be “minus,” or “electricised negatively,” if it has an “under quantity” of electrical matter. With the particles equally distributed, there will be a neutral condition. Further, although the electrical fluid might move from one location to another, its overall quantity will remain constant. With his new way of thinking about electricity as invisible particles in motion, Franklin explained that “Mr. Musschenbroek’s wonderful bottle” works because there is an abundance of electrical fluid on the inside of the glass and a corresponding deficiency on the outside.25 In fact, he could produce the same effect as he could with a Leyden jar by using a flat pane of glass with thin metal foil on its top and bottom (a device that would also be used to study animal electricity, and one that would become known as the “Franklin square,” among other names). Hence, Franklin now felt that he could do better than his contemporaries when it came to explaining thunder and lightning storms. His basic idea was that lightning would shoot up from the overcharged earth to the undercharged clouds to restore the equilibrium, with an explosion occurring (like that of a Leyden jar, only greater) with contact and the restoration of the equilibrium. In brief, Franklin began to view lightning as being the same as manmade electricity but for its quantity. But could the similarity be proved? That is, could this idea, which some others were also endorsing, be put to the test? By this time, Franklin knew there was good indirect evidence for the association. He would, in fact, write: “Electricity agrees with lightning in these particulars: 1. Giving light. 2. Colour of the light. 3. Crooked direction. 4. Swift motion. 5. Being conducted by metals. 6. Crack or noise in exploding. 7. Subsisting in water or ice. 8. Rending bodies it passes through. 9. Destroying animals. 10. Melting metals. 11. Firing inflammable substances. 12. Sulphurous smell.”26 But could it charge a Leyden jar and show similar features to frictional electricity after being “captured”? After thinking the issue through, Franklin published a plan on how lightning could be captured using a tall vertical rod, his so-called sentry box experiment (Fig. 13.10). Shortly thereafter, in 1752, Thomas-François d’Alibard (1703–1799) did it in Franklin’s suggested way in France, while Franklin, in a variation of this experiment and not knowing what d’Alibard had just done, proceeded to do the same thing using a kite rigged with a wire rod and by placing a metal key at the earthly end of the string (Fig. 13.11).27 It was thus demonstrated that lightning could charge a Leyden jar, and that it could produce the same effects as the electricity (p.210)

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The Increasingly Electrical World generated by rubbing a glass tube —effects that even included ringing bells.28

Franklin was instrumental in widening the known electrical world, which is why we are giving him special attention in this book. He proved with experiments that electricity is not just an artificial force, but also a power that exists in raw nature. A question that would now generate considerable debate is whether it also exists in living nature. And even if suspected, could such a thing be proved? At this juncture, it is worth noting that Franklin’s contributions to the study of electricity would involve more than just studying lightning and the physics of electricity. As we shall see below, he also Figure 13.10: A “sentry box” with a tall conducted clinical “tryals” to pole for capturing electricity from the determine if electricity might heavens as illustrated in Franklin’s have utility in medicine. pamphlet from 1751. Moreover, he was also directly involved in testing the idea that some living creatures, notably some shocking fishes, might be electrical, the subject of our next chapter. But before we set forth to explore these topics, two more things about Franklin must be noted to give proper color to the picture we are trying to paint about electricity’s emergence as an alternative to the animal spirit notions we have been discussing. The first is that, in addition to receiving numerous honorary degrees from American and European universities, Franklin was awarded the Royal Society’s Copley Medal in 1753 and was elected a Fellow of the Royal Society in 1756.29 (p.211)

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The Increasingly Electrical World As noted in a previous chapter, the Royal Society emphasized the power of careful experiments to establish basic facts, as opposed to loose, magical, and occult thinking. This no-nonsense, highly empirical orientation was basic to Franklin’s approach to science and medicine, and it would figure prominently in the demise of earlier animal spirit ideas.

Our second important point, which might seem obvious to some readers at this juncture, is that Franklin’s discoveries and thoughts about electricity were widely disseminated by him and those in his circle. Not only did

Figure 13.11: The Currier & Ives illustration of Franklin’s famous 1752 kite experiment. Franklin is shown with his bastard son William (1731–1813), who was actually 20 years old at the time,

he send letters to assisting and serving as a witness. correspondents around the world, his formal communications were read before the Royal Society, and published both in the Philosophical Transactions of the Royal Society and in a more general periodical with a broader readership, The Gentleman’s Magazine.30 They were also compiled in a widely read pamphlet, his Experiments and Observations on Electricity, which first appeared in 1751 and then underwent multiple editions, including in French and other languages (Fig. 13.12).31 To say the least, Franklin’s impact on the field via these writings and less formal oral communications was enormous. His authority would help pave the way for people to think about and also accept some new ideas about electricity. One, of special interest to us, would be his belief that some fishes are, in fact, electrical —a subject of immense importance for moving physiology away from earlier animal spirit ideas.

Earthquakes and Plant Electricity Stimulated by Franklin’s work, but by no means solely because of it, natural philosophers could not help but wonder whether electricity might be the cause of a wide variety of physical phenomena.32 Looking towards the heavens, not only might thunder and lightning be electrical, but so could meteors and “fireballs.” Further, it now seemed that the aurora borealis and australis—the northern and southern polar lights with their dazzling colors—could be electrical.

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The Increasingly Electrical World But questioning eyes were not just turned upwards towards the heavens. Some were gazing lower with the thought that electricity could explain volcanoes and even earthquakes.33 A great interest in earthquakes had stemmed from what Newton had written about his aether also being under the ground (Chapter 9), and it intensified after London suffered a notable earthquake early in 1749. This led the Royal Society to look into the matter and, as reported by William Stukeley (1687–1765), who participated in the sponsored discussions and debates that ensued, this timely topic drew record attendance. (p.212)

Figure 13.12: The fifth (1776) edition of Franklin’s pamphlet on electricity, first published in 1751.

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The Increasingly Electrical World One of the ideas that had been bandied about prior to this time was that earthquakes are due to the kindling of sulfurous vapors trapped in the earth. Lightning, increasingly seen as a burst of electricity from a highly charged atmosphere, was in this way tied to earthquakes. After all, as put by Franklin’s protégé, Joseph Priestley (1733–1804) (Fig. 13.13):

May not the void space above the clouds be always occupied with an electricity opposite to that of the earth? And may not thunder, earthquakes, etc. be occasioned by the rushing of the electric fluid between them whenever the redundancy of ether is excessive? Is not the aurora borealis and other electrical meteors, which are remarkably bright and frequent before earthquakes, some evidence of this?34

Figure 13.13: Joseph Priestley (1733– 1804), Franklin’s protégé and author (with Franklin’s help) of an early history

Stukeley, a leading promoter of of electricity. the electrical earthquake theory, published several papers presenting his personal philosophical position in a special supplement to the Philosophical Transactions, which contained 57 articles.35 He attributed earthquakes to massive electrical shocks caused by electrical imbalances between the electrified earth and the non-electric clouds. There were, of course, variations on his theme, one being that the electricity travels from more to less electrified parts of the earth itself.

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The Increasingly Electrical World As can be imagined, some natural philosophers constructed electrical earthquake models. Joseph Priestley, who questioned the specifics of Stukeley’s conception, made several, and he described his efforts in this exciting branch of natural philosophy in the 1767 edition of his monumental History of Electricity.36 He thought that high-flying kites rigged with wires, like the one Franklin had flown in Philadelphia, might even be a means of preventing or controlling earthquakes. Others wondered whether lightning rods, by attracting electricity, might actually prove harmful by increasing the number of earthquakes. Of special importance for us, the general excitement about electricity was now also starting to spread to living nature. In this regard, the “motions” of some plants caught Robert Turner’s (fl. 1740s) attention. In 1746, the same year in which van Musschenbroek discovered the Leyden jar and Franklin began his forays into electricity, Turner published his Electricology: Or, A Discourse upon Electricity (Fig. 13.14). (p.213)

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The Increasingly Electrical World His stated goal was to “proceed to apply Electricity to the solution of some surprising Phaenomena, which have not as yet been accounted for, in any satisfactory manner.”37 Although his book is filled with electrical experiments, the proofs behind his explanations disturbed some of his more learned colleagues, who quickly saw the flaws in his rather loose logic.

Turner found one such phenomenon in “the Sensitive Plant, whose Frame and Texture, is so very nice and Tender, that, at the least touch of the Finger, it will contract its Leaves, as if sensible of the Contact.”38 Turner was referring to the mimosa, a plant with touch-sensitive leaves, and he felt he now knew how to explain its contractile actions. He wrote about “a most fine, subtile and invisible Fluid, diffus’d through the whole Expansion of Space; also, endued with the highest Degree of Elasticity, and, does by its Spring and Subtilty, easily pervade, and run through the Pores and Interstices of all

Figure 13.14: Robert Turner’s Electricology: Or, A Discourse upon Electricity, published in 1746.

Bodies in the Universe.”39 To Turner, the key had to be electricity, which was firmly tied to the Newton’s concept of a universal aether. Specifically, Turner wrote that this plant builds up an electrical “virtue” (charge), and that when it is touched it discharges, causing the leaves to distend. The leaves will remain limp until they can again build up a sufficient “Quantity of the Virtue,” meaning an adequate amount of the subtle, invisible, and elastic aether pervading the universe.

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The Increasingly Electrical World What is perhaps most startling here is that Turner had no direct evidence from the mimosa to support his bold assertion. All he really knew was how its leaves would respond upon being touched. His further experimental support was even more indirect. It involved charging a feather, which seemed to resemble a mimosa leaf, and then touching it, causing its plume to collapse. “The Feather, as it [again] receives the Virtue from the Machine, will open and expand itself by Degrees, till it has quite recover’d its former Shape, and at the Touch of a Finger shut up again.” “Just so acts the Sensitive Plant,” which contains “this Virtue Naturally,” he explains.40 It is worth noting that some natural philosophers, including Nollet, would claim that mild electricity could speed the germination of seeds and cause plants to grow their shoots and roots faster, the underlying thought being that it might enhance the movements of sap. This was another way in which electricity was tied to plants and vegetables at this time, even plants that are not endowed with as much electricity as the touch-sensitive mimosa seemed to be to Turner. The belief that some plants, such as nasturtiums and marigolds, could give off flashes of light at dusk, added to the ongoing speculations about plants drawing electricity (respiring) from the atmosphere.

Medical Electricity, Suffering Humanity, and the Nerves Staying with Turner, he concluded his 42-page discourse on electricity with a brief statement about the medical potential of electricity, a development then in its infancy. In terms of the bigger picture, and specifically the one we wish to provide about the ultimate demise of loose animal spirit ideas, this subject also merits attention for several reasons. After all, would it still be quite so farfetched to think that the mysterious fluid of the nerves might be electricity or a closely related force if electricity could repair or reconstitute injured or diseased nerves? Additionally, if electrical stimulation from machines and the discharges of some shocking fishes could be shown to have similar healing effects (such (p. 214) as relieving pain or a palsy), could this not be construed as more evidence to suggest that at least some living creatures are electrical? The therapeutic use of electric fish discharges dates quite far back, at the least to the first century AD. This was when a freedman by the name of Anteros accidentally stepped on a live torpedo ray that had been beached in his native Italy (for pictures of electric rays and other strongly electric fishes, see Chapter 14).41 To his amazement, the shocks he received seemed to relieve his podagra, the term for foot pains associated with arthritic conditions, especially gout, at this time. Scribonius Largus (c. 3 BCE–c. 54 AD), the Roman physician who provided this information in his Compositiones medicae, written about 54 AD, also found reason to recommend live torpedoes for treating a second kind of pain, the dull pain associated with headaches.42

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The Increasingly Electrical World Others now began to recommend torpedoes for these and other conditions. In this regard, Dioscorides of Anazarbos (fl. 60–70 AD) came forth with an important pharmacopoeia in the first century.43 In it, he wrote that torpedoes could be used to treat a prolapsed “seat” (most likely hemorrhoids, but possibly intestinal prolapse as well), a treatment also favored by Galen for this condition. These live-fish prescriptions continued to be recommended during the Byzantine period (e.g., by Marcellus of Bordeaux, Aëtius of Amida), although ointments made by boiling them, and hence not just their shocks, were also prescribed (e.g., by Alexander of Tralles). Middle Eastern physicians continued to recommend live electric fishes for podagra, headache, and other medical disorders. In some instances, it is clear that the ra’ad recommended is not a torpedo ray common to the Mediterranean but the electric catfish, which can be found in the Nile and several other warm African rivers and lakes. Abu Yahya Zakariya’ ibn Muhammad al-Qazwīnī (1203– 1283), a physician who practiced in Persia and Baghdad, for example, noted that the ra’ad is used to cure fevers in “India,” a term that in his day signified multiple places, including Ethiopia, the site of Lake Tana and source of the Blue Nile, both of which contain the electric catfish. Nevertheless, the use of electrical machines for treating illnesses and diseases with mild shocks, or by drawing sparks from a charged human body, did not stem from the idea that a few fishes used therapeutically in the distant past might have been electrical. First, the idea of using the shocks of live torpedoes or electric catfishes to treat various conditions had disappeared from the mainstream Western medical literature well before the mid-1700s. And second, a closer look at the chronology will reveal that medical electricity actually emerged slightly before respected natural philosophers began to entertain the idea that some fishes might be electrical. To appreciate what transpired, we must stress that 18th-century natural philosophers were guided by the idea that even seemingly mundane discoveries could have some utility. This was one of the driving forces of the scientific Enlightenment, and it was one reason why even people with little education in far-off lands were so interested in nature. But, as many people wondered, just what uses might there be for electricity? Seeing that a spark from an electrical machine could make a limb twitch might have provided an initial clue here. If electricity could cause twitching in a healthy person, perhaps it could also affect the nerves and muscles of people with paralyses, possibly restoring long-lost movements when other therapies failed.

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The Increasingly Electrical World Johann Gottlob Krüger (1715–1759), a professor of philosophy and medicine in the German city of Halle, was instrumental in starting what became an electrical therapeutics fad.44 In 1743, he told his students that “all things must have a usefulness: that is certain. Since electricity must have a usefulness, and we have seen it cannot be looked for either in theology or in jurisprudence, there is obviously nothing left but medicine.” He even opined: “The best effect would be found in paralyzed limbs.”45 In 1744, the very year in which Krüger’s lectures were published, Christian Gottlieb Kratzenstein (1723–1795), one of his more attentive students, tried using electricity on a few patients with movement disorders, probably due to arthritic conditions. Electrification for 15 minutes was all one woman required to overcome a finger contraction, whereas a man with two lame fingers found that he could play his harpsichord again after undergoing treatment. Kratzenstein published his findings a year later and they caused a considerable stir.46 As might be expected, what seemed like a miracle cure quickly drew wide attention, partly because of how ineffective the “heroic” medical practices of bleeding, purging, and blistering had been when it came to treating arthritis, the palsies, and other chronic disorders, and partly because it was economical and seemingly safe. The bar was raised even higher when Jean Jallabert (1712– 1768), a professor in Geneva, reported a notable success with a locksmith who had lost movement on the right side of his body years earlier in an accident.47 The advent of the small Leyden jar for storing varying amounts of electricity was also of great significance in the growth of electrical bedside medicine, giving therapists even more control over the shocks they would administer (Fig. 13.15). Among the well-educated elite, the therapeutic actions of electricity for such things as paralyses tended to be tied to nerve channels and the Newtonian idea of matter in motion. The basic thought was that electricity must somehow have the ability to unblock the blocked channels that are impairing nerve function. With most people still focused on a fluid in the nerves, as opposed to the solids in the nerve core, these blockages were often thought to be due to the nerve fluid becoming too turgid, which would impair the transmission of the animal spirit. It was further believed that the (p.215)

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The Increasingly Electrical World nerves could become flaccid in some disorders (e.g., melancholia, hysteria), something that could be treated by proper stimulation. Of course, actual physical damage to the nerves, such as from a bullet or saber wound, could also disrupt function, although electricity would be considerably less effective in treating these injurybased physical conditions.

Not only was it believed that electricity might tighten flaccid nerves, but in the 1745 Gentleman’s Magazine article that Peter Collinson sent to Franklin, readers were informed that “It has already been discover’d, or believ’d to be so, that electricity accelerates the movement of water in a pipe.” Readers were also told that electricity could cause blood to flow more freely from a cut vein. Robert Turner, who we mentioned above, explained: “Several who have been let Blood, have, when Electrified, bled more freely

Figure 13.15: A young woman undergoing treatment with medical electricity. This illustration comes from the third edition of instrument maker George Adam’s (c. 1720–1773) An Essay on Electricity of 1792, which contains a paper by surgeon John Birch (1745–1815) on medical electricity. Although of later date, it shows the basics for electrotherapy by mid-century: a machine for producing static electricity, a Leyden jar for storing it, and electrodes for releasing it on a select part of the patient’s body. The treatment sessions sometimes involved family and friends to comfort the patient, as can be seen here.

than before.”48 Hence, electricity should also cause turgid, viscid, and stagnated nerve fluids to flow more freely by clearing blockages in the nerve core. As put in the anonymous article in Gentleman’s Magazine, all of this would suggest that “There are hopes for finding a remedy for the sciatica or palsy.”49

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The Increasingly Electrical World Theory was not, however, the driving force for every practitioner drawn to this new sort of therapy. In particular, therapists who did not possess medical degrees tended to be more empirical or results-oriented than theory-oriented. Consider Franklin, who had only a few years of schooling and experimented with the new therapy. He really only cared about two things: whether medical electricity could be administered safely, and whether it worked. He was quite content to leave why it might or might not work to his better-educated physician friends. They, in turn, would now also be required to think long and hard about what these and other new discoveries in the field of electricity might be telling them about living nature and, more to the point, their favorite animal spirit ideas. Franklin was, in fact, one of the first electrotherapists.50 Starting in the late 1740s, he began to treat palsied patients in and near Philadelphia, including two men who had been prominent in colonial politics and even served as governors.51 In 1757, after arriving in London, he wrote a letter to the Royal Society about his experiences with palsied patients. He stated he found that paralyzed limbs felt warmer after treatment, and that they “were found more capable of voluntary Motion, and seem’d to receive Strength.” He even described a man who could not “lift the lame Hand off his Knee,” and how he, “on the fifth Day was able, but with a feeble languid Motion, to take off his Hat.” He explained: “These Appearances gave great Spirits to the Patients, and made them hope a perfect Cure.” But, he went on, this illusion was soon shattered. He stressed that, at least for paralytic disorders of long duration, he “never knew any Advantage from Electricity that was permanent.” Exercise and high expectations, he opined later in his formal letter, probably accounted for the temporary improvement. Franklin’s letter was published a year later.52 Abbé Nollet, who at first thought that electricity might cure paralyses, was also becoming skeptical about some of the initial claims that had been made about electricity’s virtues by this time. He had previously found, just Franklin now reported, that hope, enthusiasm, and expectations might account for some temporary positive outcomes.53 (p.216) Although Franklin also failed to find electricity effective in curing deafness caused by smallpox, or the signs of what might have been a brain tumor or abscess, he had a notable success when he treated a young woman with hysteria.54 For years, C.B. suffered from “convulsions” and “almost the whole train [of] hysteric symptoms.” When Franklin and Cadwalader Evans (1716–1773), a young Philadelphia physician, treated her with gentle shocks in 1752, they obtained a long-term cure.

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The Increasingly Electrical World Interestingly, one of the first papers Franklin heard when he began to attend the meetings of the Royal Society involved a young woman with hysterical palsy, who was cured with the application of electricity.55 But here it must be remembered that hysteria was looked upon in a very different way in the mid-18th century than it is now. To many practitioners, hysteria was a real disorder of the physical machinery of the body, albeit one caused by mental factors, such as the unnatural stresses of city life (unlike their urban sisters, farmwomen rarely showed it), not the imagined physical disorder today classified as a “conversion reaction.”56 The important point for readers of this book is not that the literature on medical electricity provided a mixed bag of results, with some individuals strongly in favor of it for almost every condition, others viewing it as just another quack remedy, and still others (like Franklin) thinking it might have merit for some but not all conditions. Nor is it the fact that this literature soon swelled with hundreds of articles, which is precisely what happened over the second half of the century. Rather, it is that it drew additional attention to electricity and, at least in some circles, served to remind people about how little was really known about nerve and muscle physiology. Further, it stimulated at least some thoughts about the nerves being electrical (see, for example, Jenty’s thinking in Chapter 10), since very small doses of electricity could trigger some of the same movements that could be witnessed under normal, natural conditions.

Animal Electricity Franklin’s proof of atmospheric electricity, the thought that some plants and even minerals (e.g., tourmaline) might be electrical, the growing belief that knowledge of electricity could explain many things in nature (e.g., earthquakes), claims about medical electricity, and Newtonian physics provided some of the Zeitgeist for the idea that there might also be electricity in the animal kingdom. This thought led some natural philosophers to try to focus on a few unusual creatures, such as fireflies and glowworms, insects that seemed to have an obvious abundance of electricity, in contrast to frogs, dogs, or human beings, where the case that could be made for electricity seemed considerably less supportable.57 But although these insects were interesting, as was the “stingcup,” a species of sea anemone, it was the study of electric fishes that quickly drew the most attention. This was because their more powerful actions, including actions at a distance, were familiar to many people and well recognized, and because their shocks felt so much like the explosive discharges from the newly invented Leyden jar.

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The Increasingly Electrical World In our next chapter, we shall look at how electric fishes became electrical, a fundamental step on the path toward establishing electricity as the mysterious and poorly defined spirit of the nerves. But before doing this, let us briefly return to Turner, the British natural philosopher who had argued, among other things, that touch-sensitive plants must be electrical. Then, to close this chapter and better set the stage for the next one, we shall comment further on how pervasive invisible forces were in 18th-century natural philosophy, and then on some of the issues that men of science were facing when trying to understand and categorize them. Starting with Turner, as noted above he tried to implicate electricity in a wide variety of natural phenomena, and he was convinced that he could demonstrate that some animals, just like some plants, had to be electrical. To drive home his point, he brought up the sea torpedo, a choice for which he deserves some credit. In his words: “the most rational and satisfactory Account for the Cause of this benumbing Property of the Fish, is deducible from the Principles of Electricity, by supposing it naturally endued with this Electric Quality, which rushes out very forcibly upon the Finger of them who touch it.”58 But Turner did not experiment with live torpedoes, and for all we know he might never have even seen or touched one, dead or alive, as they are uncommon off the English coast and rarely enter the Thames River.59 Not one to be held back by a lack of direct evidence, Turner turned to the ubiquitous flounder, which is also a flat saltwater fish. Easily caught in the waters off England, his intent was to transform a flounder into what he described as an “artificial Torpedo” by electrifying it. When he did this and then touched the charged fish with his finger, he received what he called “a stroke, or something like a Numbness…to the Hand.” The sensation, confined to the touching limb, quickly disappeared, just as others had described when they touched small Mediterranean or French Atlantic torpedoes. Turner also tried touching his charged flounder with various objects, but he seemed to know little about conductors and non-conductors of electricity, attributing the differences he experienced to whether the intervening object was soft or hard. To quote: “As the Torpedo conveys its numbness to the Hand, through hard and dense Bodies; but not thro’ soft ones: So when the Flounder is touch’d with a long piece of Iron, the benumbing Stroke is felt, but nothing is perceiv’d when touch’d with a soft Stick, tho’ but six Inches long.”60 Additionally: “If the Torpedo be touch’d thro’ the Interposition (p.217) of any thin Body, as Cloth etc. the Stroke is felt considerably: In the same manner it happens to the Person’s Hand, who touches the Flounder with a Glove on.”61 To say the least, Turner was optimistic that these experiments would “set the Matter of the Torpedo’s being an electrified Fish by Nature…beyond all further dispute.”62

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The Increasingly Electrical World Not stopping here, he now raised the issue of how the torpedo might “be electrified by Nature.” Here he drew from Newton’s thinking, pointing to a universal fluid, an electrical fluid, that he believed the unknowing fish accumulated through its pores. With his vivid imagination, he added: Nor is this Supposition at all ridiculous, for not only a few inanimate Bodies, as Amber, Glass, etc. but many animate ones, as Cats, Horses etc. and even some Men themselves have been found to be Electric. If so, why may not some Vegetables? Some Fish?63 Turner, of course, proved nothing he was claiming. He neither provided evidence for the torpedo being electrical, nor a good explanation for how it might accumulate electricity from an outside source. In fact, he showed no more than that a flounder, like a charged feather or a suspended boy in one of Stephen Gray’s electrical demonstrations, could hold an electric charge and release it when touched directly or through certain intermediaries, perhaps even across a small air gap. Nevertheless, what he did with his artificial torpedo was very much part of the Zeitgeist that led people to think about invisible forces and various notions intrinsic to the animal spirit doctrine. Consequently, even Turner, with his flimsy “evidence” and illogical jumps, helped to provide a platform for thinking in revolutionary new ways about nerve and muscle physiology.

Invisible Forces in Perspective Let us now turn to the extent to which invisible forces, of which electricity is one of many, had been like an obsession throughout the long 18th century. These forces were often thought of as fluids or fluid-like, and there were many of them, real and imaginary. As put by historian Robert Darnton, scientists during this century found themselves “surrounded by wonderful, invisible forces: Newton’s gravity, made intelligible by Voltaire; Franklin’s electricity, popularized by a fad for lightning rods and by demonstrations in the fashionable lyceums and museums of Paris; the miraculous gases of the Charliéres and Montgolfières that astonished Europe by lifting man into the air for the first time in 1783.”64 Darnton further (and appropriately) points out that, “if they desired inspiration from a still greater authority, they could read Newton’s description of the `most subtle spirit which pervades and lies hid in all gross bodies’ in the fantastic last paragraph of his Principia (1713 edition) or in the later queries of his Opticks.” “In fact,” continues Darnton, who seems a bit overwhelmed by what his research has revealed, “there were enough fluids, sponsored by enough philosophers, to make an eighteenth-century reader’s head swim.”65

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The Increasingly Electrical World Needless to say, many issues related to these invisible forces would have to be ironed out on the winding path from earlier animal spirit notions to animal electricity. One is whether some of these forces might be related. Here we might recall that, when Newton came forth with his great inference, his atomistic conception of an intervening aether, he was doing more than just trying to explain gravity. He was also attempting to explain the actions of several seemingly related but invisible forces, including magnetism and electricity, which could pervade the universe and could also have effects at a distance. In particular, the Greek element fire, which the ancients felt was closely related to light, was believed to be closely related to electricity, or perhaps even be another expression of it, during the 18th century. Spencer, whose series of lectures on electricity inspired Franklin, certainly believed this. As expressed by Dutch physicist Willem Jacob Van 's Gravesande (1688–1742) in the 1747 (English) edition of his text, Mathematical Elements of Natural Philosophy, Confirmed by Experiments: Or An Introduction to Sir Isaac Newton’s Philosophy: There are several very remarkable Phaenomena, which are ascrib’d to the Fire contain’d in Bodies; some of which ought to be mention’d here: Amongst which there are such as have a near Relation to Electricity; for which we must also treat of the Phaenomena of Electricity…I shall only mention a few experiments…to make manifest the Connexion between the Cause of Electricity and Fire, if these two ought really to be distinguished.66 In this context, Franz Anton Mesmer (1734–1815), whose Mesmeric “system” and impact are the real focus of Darton’s book, is particularly worthy of mention. Born in 1734 in Swabia, Mesmer (Fig. 13.16) trained in medicine and initially practiced in Vienna before being forced out and moving to Paris. There he continued to promote his own invisible force, which he first called “animal gravity” and then “animal magnetism.”67 Mesmer viewed his force as consistent with Newton’s idea that invisible, subtle fluids pervade and influence the world and our bodies (see Chapter 9). But he went well (p.218)

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The Increasingly Electrical World

Figure 13.16: Franz Anton Mesmer (1734–1815), who called the invisible force that he maintained he could manipulate “animal gravity” and then “animal magnetism.” In 1784, Franklin, Lavoisier, and other Commissioners asked to do so by the French government would set forth to test Mesmer’s theory. Although they debunked Mesmer’s physical theory, they still concluded that Mesmerism could cure some (gullible) people.

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The Increasingly Electrical World beyond most Newtonians when he further claimed that some people are endowed with special powers that enable them to manipulate this force, so they could treat people suffering from various ailments ranging from the hysterias to true blindness and lameness. Mesmer, as might be expected, was one of those especially gifted healers and he was not bashful about telling people so and charging fees for his services.

Chapters and volumes have been written about how Mesmer cured some patients by touching them with his hands or his “magic” (iron) wand, or even by directing his animal magnetism at them from a fair distance away.68 Much has also been made about his avarice and how he treated many paying patients at once with a special tub filled with water and iron filings, which he called the

Figure 13.17: A late-18th-century illustration of a séance showing a baquet and people holding on to iron rods in it, while being treated by the therapist.

baquet (Fig. 13.17).69 Suffice it to say that, although Mesmer believed he had made one of the greatest discoveries of all time, not everyone familiar with him, his imaginary force, or his therapeutics agreed with his personal assessment. In 1784, the uproar in Paris and the secretiveness associated with some of the organizations endorsing Mesmer’s work forced the king, Louis XVI (1754–1793), to sanction a formal investigation into Mesmer’s claims and practices (three committees were ultimately set up). Headed by highly respected (but clearly skeptical) American ambassador Benjamin Franklin, and with famed chemist Antoine Lavoisier (1743–1794) also designing experiments, the committee members first tried to detect the invisible magnetic force with various physical instruments, only to fail. They also performed many clever experiments on patients and even themselves, some with innovative double-blind testing, before concluding that there is no animal magnetism. Although a number of sick people (mainly hysterics and hypochondriacs) were, in fact, helped, the investigators concluded that this was mainly due to imagination, (p.219) gullibility, and suggestion. As put by Franklin and the other commissioners:

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The Increasingly Electrical World It is a well-known adage, that in physic as well as religion, men are saved by faith. This faith is the product of the imagination.70 What transpired with Mesmer is often presented in the context of the history of hypnosis and how manipulating the mind ultimately entered mainstream Western medicine. Rarely do we find it tied to the animal spirit theory, although Mesmer’s invisible force might be looked upon as a variant and perhaps in some ways as even the final blaze from the dying embers of this embattled doctrine. But a closer look at what Mesmer was promoting reveals that he was not at all certain that his force and Franklin’s electricity were very different at all—that he was not completely wrong. In his writings, Mesmer tried to relate his invisible force to other forces. He explained that his subtle but powerful force had, under different circumstances, been associated with gravity, fire, light, and magnetism, sounding more than a bit like Newton, whose ideas we described in Chapter 9. And of particular interest to Franklin, he also thought that electricity, which by this time had also become a very popular method of treating the sick, might be no more than a facet or subspecies of what he was calling animal magnetism.71 Specifically, Mesmer claimed that his “system will furnish fresh explanations as to the nature of Fire and Light and Heat,…and the magnet and electricity.”72 Right after providing this thought, he added: “The magnet and artificial electricity only have, as regards sickness, qualities which they share with several agents provided by Nature, and if useful effects have been provided by the latter, they are due primarily to Animal Magnetism.” Even his therapeutic setup and how he manipulated his invisible and universal fluid with long iron rods and his shorter iron wand resembled how patients were then being treated with Leyden jars, with their electrical fluid contents, metal wires, and electrodes. In effect, “the electricians and the mesmerists saw the world in a similar way,” a world in which “a single [invisible] force could produce manifold effects.”73 These were among the reasons why Mesmer was eager to talk with Franklin when they were both in Paris (which he did). And, of great importance, it shows how natural philosophers continued to wrestle over how to classify their chosen invisible forces, which seemed to have many commonalities with other invisible forces, into the tumultuous closing decades of a century marked by revolutions. As we shall now see, natural philosophers would continue to ponder and debate what should and should not be included under the heading “electricity,” as well as whether there might even be a family composed of slightly different electricities. In this domain, one of the most pressing issues would be whether animal electricity is identical to or different in some qualitative ways from frictional or atmospheric electricity. Page 31 of 38

The Increasingly Electrical World But this is jumping ahead too fast. In our next chapter, we shall first examine what attracted 18th-century researchers to the torporific rays and numbing catfishes that had intrigued the ancient Egyptians, Greeks, and Romans, and to a species that remained unknown to Westerners until the Age of Exploration, the electric eel from South America. We shall look at what led these men to think that these creatures might release electricity, or at least something very closely related to true electricity. And, as we shall discover, the Reverend John Wesley (1703–1791), the saver of bodies and souls quoted at the start of this chapter, probably had yet another reason, namely some very strange fishes, to conclude that electricity could rightfully be called the “soul of the universe.”74 (p.220) Notes:

(1) Gilberti, 1600. (2) Many informative books and articles have been written about early electrical machines. See Walker, 1936; Hackmann, 1978; Heilbron, 1979. (3) Guericke, 1672. (4) Hawksbee, 1709. (5) Canton, 1753, 1754. (6) Gray, 1731. (7) Van Musschenbroek, 1746, 1762. For secondary sources describing the discovery of the Leyden jar, see Brazier, 1984; Dorsman and Grommelin, 1957; Hackmann, 1978. (8) From van Musschenbroek, 1746, p. 6. (9) For example, his Essai sur l’Électricité des Corps (Nollet, 1746a). (10) For more information on Nollet and electricity, see Quegnon, 1925; Torlais, 1954; Bertucci, 2006. (11) During the 1740s, Benjamin Franklin, in Philadelphia, coined the term “battery” for a collection of Leyden jars wired together so they would discharge all at once. The same term would later be applied to Alessandro Volta’s (1800) new “pile,” a different sort of battery made of stacks of dissimilar metal disks that could produce a stream of electricity. Volta’s path to his new battery is discussed in Chapter 15. (12) Nollet, 1746b, p. 18; trans. in Heilbron, 1999, p. 318. (13) Shows and lectures on electricity became somewhat of a rage during the 1700s. See Hackmann, 1978; Heilbron, 1979; Schaffer, 1983, 1993; Bertucci & Pancaldi, 2001; Bertucci, 2006. Page 32 of 38

The Increasingly Electrical World (14) Schaffer, 1993, p. 490. (15) There are many biographies of Franklin. The classic in the field is by Van Doren, published in 1938. Three newer biographies are by Brands, 2002, Isaacson, 2003, and Wood, 2004. Among the more specialized books, Finger (2006a) examines Franklin’s life in the context of his knowledge of, and contributions to, medicine. (16) Franklin incorrectly identified the itinerant showman as “Spence ”in his popular autobiography (e.g., p. 94 in the 1996 reprint). In various books, he is presented either as Adam or Archibald Spencer, who died in 1760. For additional information about Spencer, his shows, and Franklin’s introduction to the wonders of electricity, see Cohen, 1943, 1990, pp. 49–53; Heathcote, 1955; Finger, 2006a, pp. 82–85. (17) I. Bernard Cohen (1990, p. 44) provides this passage from the notes of William Black and some material from a second set of his notes. He also relates that Franklin’s Library Company in Philadelphia possesses some unlabeled notes about Spencer’s lectures by John Smith. The latter described what transpired in Philadelphia in considerable detail, also mentioning how Spencer included the suspended boy experiment in his show. Smith’s informative material is presented right after Black is mentioned (pp. 44–49). (18) Cohen, 1943, p. 6. (19) Anon., 1745. Scholars point to Albrecht von Haller as the source for the Gentleman’s Magazine publication. (20) The Library Company was formed in Philadelphia so that tradesmen could share their resources to buy books, which could then be used by members of the group interested in bettering themselves. Many of the early acquisitions dealt with natural philosophy. For more on Franklin and his Library Company, see Cohen, 1943, Heathcote, 1955, and Heilbron, 1979. (21) Labaree, 1961a, pp. 118–119. Leonard W. Labaree was the senior editor of the first few of many volumes of The Papers of Benjamin Franklin, published by Yale University Press. These letters are now available online at Franklinpapers.org. (22) David Hall (1714–1772), originally from Edinburgh. (23) Franklin did not patent his other notable inventions either. He openly claimed that his motive was to help suffering humanity, a popular philanthropic theme during the Enlightenment. (24) Du Fay, 1735.

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The Increasingly Electrical World (25) Labaree, 1961a, pp. 156–165. (26) Labaree, 1962, pp. 523–524. (27) Joseph Priestley, who wrote his text on the history of electricity with Franklin’s help, described the kite experiment in 1767. For additional information on what Franklin did with only his son William at his side, see Labaree, 1961b, pp. 366–367; Cohen, 1990, pp. 66–158. (28) Labaree, 1962, p. 69. (29) Franklin would sign the book and become an “official” member of the Royal Society after moving to London in 1757 (see Van Doren, 1938). Since he was from the British North American colonies, he was never classified as a foreign member. Starting in 1759, he would go on to nominate at least 36 other natural philosophers for membership in the Royal Society, most having done at least some research on electricity. (30) The Gentleman’s Magazine is often referred to as Gentleman’s Magazine, and we shall use this periodical’s shortened title henceforth. (31) Franklin, 1751; e.g., Franklin, 1774. (32) Ritterbush, 1964, pp. 15–56. (33) This point is made by Schaffer, 1983, pp. 15–22. (34) Priestley, 1767, p. 498. (35) Stukeley, 1750a,b,c. (36) Priestley, 1767. (37) Turner, 1746, p. 25. (38) Ibid., p. 25. (39) Ibid., p. 8. (40) Ibid., p. 26. (41) For a detailed review of the early history of torpedinal therapy with translations and extensive referencing, see Finger and Piccolino, 2011. Among other things, this co-authored book examines what Galen, Marcellus of Bordeaux, Aëtius of Amida, Alexander of Tralles, al-Qazwīnī, and other writers from the distant past thought and wrote about torpedo rays and other “not-yet electric” fishes. The authors of the present book are particularly indebted to Marco Piccolino for making available his broad knowledge and insights about electric fishes throughout history. Page 34 of 38

The Increasingly Electrical World (42) Scribonius Largus, 1983, XI, p. 18; Finger and Piccolino, 2011, pp. 45–49. (43) For an early printed edition, see Dioscorides, 1527. (44) Krüger, 1744; also see Licht, 1967; Bertucci, 2001, pp. 43–68. (45) This English translation of Krüger’s (1844) call for electrical medicine, especially for paralyses, comes from Licht (1967, p. 5). (46) Kratzenstein, 1745. (47) Jallabert, 1748. (48) Turner, 1746, p. 39. (49) Anon., 1745, p. 197. (50) It would be a mistake to call the ancients who used torpedoes or electric catfishes “electrotherapists,” because they did not view therapeutic fishes as electrical. The same can be said about others who used electric fishes prior to the middle of the 18th century. (51) Finger, 2006a, pp. 80–101, 2006b,c, 2007. (52) Franklin, 1758. (53) Nollet, 1746a, 1749a,b; Bertucci, 2006, 2007. (54) Evans, 1757; Finger, 2006a, pp. 102–108, 2006b,c, 2007. (55) Brydone, 1757. (56) John Wesley (1703–1791), the founder of the Methodist Church, who was also involved with electrical therapies in this era, wrote in his Primitive Physic that “the slow and lasting passions, such as grief and hopeless love, bring on chronical diseases.” Wesley’s book first appeared in 1747 and it went through many editions. This quotation can be found on page xii of the 22nd edition, published in Philadelphia in 1791. (57) Ritterbush, 1964, pp. 28–43. (58) Turner, 1746, pp. 27–28.

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The Increasingly Electrical World (59) John Walsh (1774), who will play a central role in the electric fish story and is a central figure our next chapter, described two large torpedoes caught off the English coast, which he considered rarities. There were also some reports of smaller torpedoes being caught in the Thames in the 1700s, but this was so exceptional that these reports made headline news. In contrast, torpedoes are fairly easily caught off the coasts of France and Italy at certain times of the year. For more about the early reports on British torpedoes, including newspaper stories and references, see Finger and Piccolino, 2011, pp. 251–252, 292–297. (60) Ibid., pp. 28–29. (61) Ibid., p. 29. (62) Ibid., p. 29. (63) Ibid., pp. 29–30. (64) Darnton, 1968, p. 10. (65) Ibid., p. 11. (66) Van ‘s Gravesande, 1747, Vol. 2, p. 72; Italics ours. The English text is based on an earlier Latin edition. (67) Mesmer, 1779, 1998 translation. Mesmer graduated from the University of Vienna in 1766. His doctoral dissertation was titled De planetarum influx in corpus humanum (“On the influence of the Planets on the Human Body”). Plagiarizing from Paracelsus in the 16th century and physician Richard Mead earlier in his own century, and strongly influenced by Newton, he argued that “there exists an allied and reciprocal influence between the Heavenly Bodies, the Earth, and all animate bodies”; that this invisible and “universal fluid” is capable of communicating movement; and that “Animal Magnetism” may be communicated and expressed to other animate and inanimate bodies from a distance (1998 trans., pp. 26–27). Mesmer saw the human body in much the same way that the 18th-century English physician George Cheyne (1733, p. 4) saw it, namely as “a Machine of an infinite Number and Variety of different Channels and Pipes, filled with various and different Liquors and Fluids, perpetually running, glideing [sic] or creeping forward, or returning backward, in a constant circle.” With his knowledge of animal magnetism, Mesmer felt enabled “to offer a new theory of illness,” as well as a safe and effective universal cure. (68) Pattie, 1956; Darnton, 1968; Buranelli, 1975; Finger, 2006a, pp. 219–250; Lanska and Lanska, 2007.

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The Increasingly Electrical World (69) Turner, 2006. The only surviving intact example of this apparatus can be found in the Musée d’Histoire de la Médecine et de la Pharmacie in Lyon, France. This survivor is a highly polished wooden tub with eight metal rods protruding from its depths and a cylindrical metal device on its top. His patients (up to 30) would sit around this baquet holding the jointed rods and/or connected to each other with a rope, while Mesmer, dressed in a flamboyant lilac silk robe, would circle the group, subjecting them to intense eye contact, twitches of his iron wand, and hand passes. Not to be overlooked, Mesmer’s treatment room was also decorated in special ways (mirrors, somber lighting, astrological images) to help assure that his patients would go into a “crisis” (e.g., convulsions, fainting), thought to be basic to the cure. He also sometimes played music on his glass armonica, an instrument invented by Franklin, or a pianoforte, maintaining in his publications that sounds can enhance the effects of his animal magnetic cures. For more on the roles of sound and music in these séances, see Mesmer, 1779, p. 27; Gallo and Finger, 2000. (70) Franklin et al., 1784, English translation, 1785; also see Tinterow, 1970, pp. 82–128 (quotation from p. 123). (71) Mesmer, 1779 (1998 trans., pp. 11–12, 27); Sutton, 1981; Finger, 2006a, pp. 226–228. (72) Mesmer, 1779 (1998 trans., p. 27). (73) Sutton, 1981, p. 392. (74) Wesley, 1760, p. 9. The same thought, slightly truncated, that electricity might only be “the soul of the world,” can be found in a poem from 1784 by Charles Marie Jean Barbaroux (1767–1794):O feu subtil, âme du monde, Bienfaisante électricité Tu remplis l’air, la terre, l’onde, Le ciel et son immensité. [Oh subtle fire, soul of the world, Beneficent electricity You fill the air, the earth, the sea, The sky and its immensity.] (Translated in Darnton, 1968, p. 29).

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Electric Fishes and the Path to Animal Electricity

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Electric Fishes and the Path to Animal Electricity C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0014

Abstract and Keywords This chapter analyzes the evidence that was gathered during the last fifty years of the 18th century about the electric charges of certain fishes. It first studies what people thought about these fishes prior to the “Age of Electrical Experiments,” including some older history and theories. It also considers generalized ideas about animal electricity, such as the thought that electricity could account for nerve and muscle physiology. Keywords:   electric charges, electric fishes, Age of Electrical Experiments, animal electricity, muscle physiology

On Thursday, the President and many Gentleman of the Royal Society were present at an exhibition of the effects of these extraordinary fish; and on Friday Mr. Walsh…obtained from the Gymnotus the electrical spark, which he never could procure from the torpedo; by which event an entire agreement in the natural effect of these animals, and the artificial effect of the Leyden phial, is established. (Notice in the Gazetteer and New Daily Advertiser, the Public Advertiser, and the Morning Chronicle and London Advertiser dated August 5 and 6, 1776)

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Electric Fishes and the Path to Animal Electricity As we have now witnessed, many natural phenomena were being seen as electrical during the middle of the 18th century, some deservedly so and others with a fair amount of imagination. The idea that some animals might be electrical began to be brought up in this scientific and even wider cultural content. The fundamental question, of course, was how to prove that any animal might be electrical, since this idea seemed to defy not just common sense but also the laws of physics, particularly given their moist bodies. Needless to say, this was an emotionally charged issue with huge ramifications. After all, if even one animal could be shown to be electrical, it would make it even more likely that others could also be electrical, although their electricity might be subtler and undetectable without sensitive instruments. And if even a single animal could be classified in this way, the once seemingly absurd notion that electricity might be involved in the basic physiology of all animal bodies would no longer be assailed as a violation of nature’s laws; the idea would, in short, seem considerably less ridiculous. The starting phase of the animal research that would lead to the shift away from earlier animal spirit ideas would not involve lightning bugs, glowworms, or any other insects or invertebrates. Nor would it be conducted on frogs, dogs, or people themselves. Rather, experimental evidence for animal electricity and ultimately nerve electricity would begin to emerge with three strange fishes, fishes that many scientists would accept as electrical by the end of the 18th century. These fishes are (a) the flat saltwater torpedo rays (Fig. 14.1), many varieties of which can be found around the globe, especially in warmer waters; (b) a single species of electric “eel” (previously Gymnotus, now Electrophorus electricus), which is actually a knifefish found in the warm rivers and pools of South America (Fig. 14.2); and (c) some electric catfishes found in the Nile and other freshwater African rivers and lakes near the equator (Fig. 14.3). Referred to as Malapterurus, and once thought to be a single species, some 19 distinct species of electric catfishes are now recognized, and the list is growing.1 These three types of fishes do not deliver shocks of the same intensity. The small torpedoes common to the Mediterranean Sea and the French Atlantic coast, for example, typically deliver shocks of 50 to 75 volts at 1 amp. There are also some larger, less common varieties of torpedoes that have stronger discharges. At about 300 volts, an electric catfish from the Nile River would take the intermediate position. And with more than twice this power, a healthy electric eel can deliver a jolt or a series of shocks that could buckle a

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Electric Fishes and the Path to Animal Electricity (p.222)

Figure 14.1: An illustration of a flat saltwater torpedo in the 1553 text, De aquatilibus, by Renaissance naturalist Pierre Belon (1517–1564).

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Electric Fishes and the Path to Animal Electricity

Figure 14.2: Laurens Theodor Gronov’s (1763) illustration of the South American electric eel, previously Gymnotus electricus and now Electrophorus electricus.

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Electric Fishes and the Path to Animal Electricity man and send even a horse into a panic, as German baron Alexander von Humboldt (1769–1859) observed during his famous journey to the New World that took him into the swamplands of what is now Venezuela.2

A major problem facing mid-18th-century naturalists and physicists was that they did not have physical instruments capable of detecting and registering these discharges (they occurred too rapidly to be picked up by threads, Canton’s pith ball electrometer, or other tools of the trade). But natural philosophers were finding that

Figure 14.3: An electric catfish (Malapterurus) as depicted in a volume by the French naturalist Baron Georges Cuvier (1769–1832) in 1834.

there are a few fishes that could give shocks that feel just like those from the newly invented Leyden jars (Chapter 13), and this was extremely important. In fact, the invention of the Leyden jar not only drew investigators to these fishes, it also provided them with a model or way of thinking about their discharges. A recurrent thought in the final quartile of the 18th century would be that these fishes must somehow function like biological Leyden jars. In this chapter we shall focus on how evidence accumulated in the second half of the 18th century for the discharges of these fishes being electrical. But to put this important development in proper perspective, we must begin with what people thought about these fishes prior to what we, like Franklin, might loosely think of as the “Age of Electrical Experiments.” Hence, we shall begin with some older history and trace theories about these fishes to the time when their discharges were widely viewed as electrical. As noted, this revelation would open the door for more generalized ideas about animal electricity, including the thought that electricity could account for our nerve and muscle physiology far better than previous notions. For a far more detailed historical treatment of the literature on strongly electric fishes with translations and extensive referencing, the interested reader is directed to a recent book co-authored by the third author of the present text.3

Ancient Thoughts The earliest depictions that we have of any of the electric fishes are the realistic tomb drawings that date from about the time of the great pyramids (built around 2550 BCE) in (p.223)

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Electric Fishes and the Path to Animal Electricity ancient Egypt.4 They show the electric catfish Malapterurus among other fishes and aquatic animals, such as crocodiles and hippopotamuses, in natural and sometimes wonderful color settings (Fig. 14.4). Yet there is nothing in these scenes of life along the Nile to suggest that the electric catfish was viewed as unique among fishes or even among the many kinds of catfishes common to Egypt.

The Ebers’ Papyrus, which provides over 800 treatments for various diseases and disorders, dates from about 1500–1600 BC but is based on far older written accounts, some of which were first

Figure 14.4: Detail of panorama from the ancient Egyptian Tomb of Ti (c. 2400 BCE), which showed a hippopotamus hunt. The electric catfish is under the back of the larger boat with a pole in front of it. It has whiskers and faces left. (Photograph courtesy of Wendy Finger)

transmitted by oral tradition.5 Prescription 304 is among the treatments for inflammations. It involves a salve made by burning the head of a dead fish and mixing it with fat or oil. The prescribed fish is called ddb or djedeb in Egyptian (other catfish salves do not specifically specify this fish), a word meaning “sting,” which could well have described what a live Malapterurus could do. Although a dead fish was used for the salve, as well as in some other catfish prescriptions (numbers 128, 250, 730), in the minds of the Egyptians this might not have precluded it from retaining some of the powers it was thought to have when alive, knowing what we do about ancient Egyptian magical and religious beliefs. There are no known hieroglyphs that clearly show an electric catfish, although the serekh (a precursor of the cartouche) of “Narmer” is intriguing because it shows a rather generalized catfish (N’r in phonetics) above a chisel (Mhr). Narmer was one of the earlier unifiers of Egypt, and he ruled in about 3150 BC. What is particularly interesting here is that the early Egyptian kings took the names of powerful and magical animals, and Narmer might have wanted to be associated with the stinging (electric) catfish, much as there had been a predynastic Scorpion King. But whether a catfish was chosen because of its benumbing powers, its association with the night or a specific early deity, or for some other reason is uncertain. Moreover, the stylized Narmer images are lacking in detail, preventing archeologists from making a strong case for his seal actually depicting the Nile’s electric catfish, as opposed to another species of catfish (some of which are huge) or catfishes in general.6

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Electric Fishes and the Path to Animal Electricity In effect, without written passages to draw on, we really know very little about what the ancient Egyptians thought about Malapterurus, a river dweller they knew quite well. With the ancient Greeks, in contrast, we encounter the earliest written descriptions of the powers of some electric fishes, although the fishes they focused on were varieties of flat sea torpedoes, not an elongated river catfish. The Greek philosopher Plato, who died in 348 BCE, compared his mentor Socrates to one of these rays in one of his most famous dialogues, Meno. This was because Socrates seemed to benumb his listeners with his logic and rhetoric, much like a torpedo might benumb a smaller fish or a gripping hand. As put by Meno after listening to Socrates: “I am benumbed in my soul and my mouth.”7 Although the Hippocratic physicians of the fifth century had recommended boiled torpedoes as an easily digested food prior to Plato, they did not describe the torpedo’s remarkable powers when alive in their surviving texts, making Plato’s analogy in the Meno that much more significant.8 The more zoologically oriented Aristotelians (e.g., Aristotle, Theophrastus), who were intrigued by how certain organisms managed to survive, focused on the natural histories of all sorts of animals soon after Plato’s death in Athens. (p. 224) In the Historia animalium, there is a wealth of information about these rays, including their “intelligence,” a term encompassing how they could catch faster-moving fishes by hiding in the sand and numbing these fishes if they unknowingly passed nearby. It was also noted that these obviously clever rays could use their powers for defense, since “the torpedo is seen to cause numbness in humans too.”9 What the author(s) of this material found truly amazing about these saltwater rays was that they could produce their effects not only willfully but at a distance—meaning through intermediaries, such as water, nets, lines, and wet or metal poles, as witnessed by fishermen. During the Roman era, the torpedo’s discharges made their way into medicine, especially for treating disorders associated with pain, such as gout and headache (see Chapter 13). At the same time, some philosophers began to try to explain the mechanisms behind the torpedo’s remarkable powers in their texts. Plutarch of Chaeronea (c. 46–127), for one, opined that the crafty torpedo “discharges its effluvia as if they were darts, and thus poisons first the water, then through the water the creature which can neither defend itself nor escape.”10 In a comparable way, Plutarch’s equally famous contemporary, Pliny the Elder (23–79), wrote that the torpedo’s power is due to an odor (or breath) or a kind of emanation (aura) of its body.11

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Electric Fishes and the Path to Animal Electricity Pliny, borrowing from the Aristotelians and others, also provided information about the behavior and biology of the torpedo. He even listed a number of medical prescriptions calling for torpedoes, although they were dead ones. Pliny was less than selective and displayed a propensity for including virtually everything he read or heard in his compilations. To say the least, some of his torpedo prescriptions would leave modern readers scratching their heads, to which we might note that he even had a torpedo prescription (more like a witch’s brew to readers today) for hair removal.12 Galen, who was born during the second century in the Greek city of Pergamum but lived most of his professional life in Rome, experimentally confirmed a place for live (but not dead) torpedoes in medicine, while extending the idea that the torpedo must release some sort of poison.13 In his De locis affectis and in his De symptomatum causis, Galen associated numbness with cold and a reduction of movement. In this context, he concluded that the torpedo must be releasing some sort of a refrigerating agent (poison or venom) that could have effects through certain intermediaries, much like the action of a lodestone or magnet, which could transmit its power to nearby iron bodies that could then affect others. He specifically compared the torpedo to poisonous spiders and scorpions, which are able to produce widespread effects with just small doses of venom. The idea of any icy venom that can congeal the blood and freeze the nerves, causing stupor and numbness, would also come forth in the poetry of Oppian of Corycus during the second century, and then Claudian (c. 370–410). For example, Oppian included these lines in his Halieutika, his five volumes about fishes and fishing, in which he also conveyed considerable information about torpedoes: The Pow’r of latent Charms the Cramp-Fish know, Tho’ soft their Bodies, and Motion slow. Unseen, foreboding Chance and future Prey, The crafty Sluggards take their silent Way. Stretcht from each Side they point their magick Wands, Whose icy Touch the strongest Fin commands; Quick thro’ the whole it shoots the rushing Pain, Freezes the Blood, and thrills in ev’ry Vein;….14

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Electric Fishes and the Path to Animal Electricity The icy venom idea also would be cited during the medieval era, and would continue to surface throughout the Renaissance. This is not to imply that thinking remained stagnant over a 1,500-year period. It did not: if anything, the torpedo became even more magical and its powers more closely associated with unknowable or occult qualities during this lengthy time span, during which it made its way into a remarkable number of books on a wide variety of subjects.15

Mechanical Notions The scientific revolution that took place during the 17th century heavily emphasized physics and mechanics. Leaders of the movement, including René Descartes in France and the Netherlands, Galileo Galilei in Italy, and Sir Isaac Newton in England, attempted to explain both physical and living phenomena with recourse to mechanical principles. This new orientation, as we have seen in earlier chapters, was reflected in the changing nature of the animal spirit doctrine over the course of this century. As noted, with Newton near the end of the century, there was a strong emphasis on movements of fine particulate matter in his hypothesized aether. Two other changes accompanied this new orientation, and they were stressed by the new scientific organizations that emerged in this century, including the Accademia del Cimento in Italy, the Royal Society in England, and the Académie Royale des Sciences in France. One was an emphasis on careful, replicable, and verifiable observations, as opposed to blindly accepting what the “authorities” of the past and even of the present had to say. And the other was great faith in the power of experiments to link causes and effects together in ways that natural philosophers believed would endure the test of time. Needless to say, there was still a tendency to speculate, but for the most part the “new science” was an inductive pursuit, proceeding from small observations and established facts to more general principles, as opposed to being guided deductively by grandiose theories, many of which these new men of science were claiming could not be substantiated. To these factors we (p.225) might add that gathering good information was increasingly viewed as a group effort—a democratic endeavor open to anyone who might want to contribute to the knowledge base, which in some way might ultimately have some utility. The first substantive steps toward explaining the curious effects of electric fishes with mechanical principles took place after the mechanical revolution had begun, and notably after Descartes’ death in 1650. It began under the auspices of the Medicis. In 1671, Francesco Redi (1626–1698), a firm believer in the power of experimentation, and a man who would spend a lifetime debunking myths, responded to some claims made by Athanasius Kircher (1602–1680), a German priest, scholar, and natural philosopher, who was defending some ancient thoughts and promoting a Jesuit scientific agenda from his headquarters in Rome.

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Electric Fishes and the Path to Animal Electricity Francesco Redi had been born in 1626, in Arezzo, Italy. The son of a man of stature who would become the personal physician of the Grand Duke of Tuscany, he studied at a Jesuit school in Florence and completed his own medical studies in Pisa in 1647. After traveling to Rome, Naples, Bologna, Padua, and Venice, he began practicing in Florence, and from 1657 until 1667 he was a member of the newly founded Accademia del Cimento (literally “Academy of Experiment”), one of the first scientific societies in the West. A brilliant man, Redi rose to become personal physician to Grand Duke Ferdinando II de Medici (1610–1670) and then to Cosimo III de Medici (1642– 1723). During his service, he conducted many experiments to improve medical and surgical practices, while also involving himself in the humanities. Not one to shy from a fight, Redi had already taken aim at Kircher’s evidence for spontaneous generation, and he was now irked by some of what the cleric had written about venoms (e.g., there being stones that could protect against their actions). The topic of venoms had led Father Kircher to write about the sea torpedo, which he thought was releasing a narcotic quality in an imperceptible way—a Galenic cold quality that he believed could restore movement to a dead fish and freeze the spirit in the veins, muscles, and nerves.16 In his text of 1671, which was written to rebut Kircher’s way of thinking, Redi focused on several of his ideas, including his thoughts about the torpedo.17 He related that he had gone with the Grand Duke to Leghorn on the Italian coast 5 years earlier, where he had access to a torpedo that caused his arm to tingle and tremble when it was touched. He also described a dissection he conducted on the torpedo, which led him to identify “two bodies, or possibly two muscles of falciform shape,” the rapid movements of which seemed to be responsible for these effects.18 Redi’s identification of the underlying organs was accurate, and it stimulated additional studies and variations on his mechanical theme. In 1678, his student Stefano Lorenzini published the first book devoted entirely to an electric fish, one that he might have written with Redi.19 Lorenzini had been given six torpedoes by the Grand Duke, and although they were vigorous, he and those with him could not feel their shocks through the water, an iron rod, or a fisherman’s net. Direct touch, in contrast, caused him considerable pain, which he attributed to “a contraction of the fibers composing the two bodies or falciform muscles.”20

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Electric Fishes and the Path to Animal Electricity In contrast to what Redi had written 7 years earlier, Lorenzini’s text is more atomistic, in that he brings up the release of minute particulate matter that can penetrate the pores of the victim and enter the canaliculi (minute nerve canals) of the body. These particles could cause pain, numbness, and movement problems, because of their sizes, shapes, and quantities, all of which could, in theory, block or damage the thin tubules. This being the time of the advent of microscopes, there was then great interest in the invisible world, and Lorenzini’s thoughts, stimulated by the great Galileo’s own atomistic thinking, fit well into this exciting new Zeitgeist. Giovanni Alfonso Borelli, who was close to Redi, also supported the idea that movements of the falciform muscles could in some way explain the torpedo’s effects.21 So did other guests and foreign visitors to the Medici court. Nevertheless, the individual who would be most closely associated with a mechanical theory of the torpedo’s actions in the first half of the 18th century was not an Italian scientist or a foreigner who had made a scientific pilgrimage to be with these savants and their powerful patrons in Italy. René-Antoine Ferchault de Réaumur (1683–1757), who was born in La Rochelle (a Huguenot town on the French Atlantic coast where torpedoes are plentiful) and died in Paris, was a revered natural philosopher.22 He became a member of the French Académie Royale des Sciences before age 25 and then served repeatedly as an officer of the prestigious organization. He was a man of diverse interests, ranging from shells and sea life to silk production, and was especially well known in his lifetime for his six-volume Mémoires pour Servir à l’Histoire des Insectes. Réaumur developed a large network of correspondents, one of whom was van Musschenbroek, who sent his description of the frightening new Leyden jar to him in 1746 (see Chapter 13). Well connected and ideally situated, Réaumur rejected the ancient idea of a cold poison and Lorenzini’s thoughts about specialized organs emitting corpuscular matter that could torpify. This was partly because he knew that torpedoes could have effects at a distance—that they could, as every local fishermen seemed to know, shock, even if only mildly, through fishing nets. More aligned with Redi and Borelli, Réaumur left atomism by the wayside and maintained that the torpedo’s powers stem directly from extremely rapid motions of its paired falciform muscles. The movements of the musculi falcati, he wrote, are so fast that even the most attentive eyes cannot see them, although the fish tenses its body, making them more convex at the time of discharge.

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Electric Fishes and the Path to Animal Electricity Réaumur’s mechanical theory, submitted to the French Académie in 1714 and published in 1717, included an illustration of the electric organ, which he described as stacks of (p.226) cylinders that could act like elastic springs when the fish readies its body to attack.23 His ideas and article would be cited again and again by people writing about electric fishes in the 18th century, including the more powerful eels of South America. It remained virtually unchallenged until the second half of this century, when many institutions and long-accepted facts of life crumbled.

The Emerging Concept of Fish Electricity The thought that some fishes might be electrical began to circulate at midcentury, although electric fishes had been loosely compared to lightning well before this time. For instance, the Arabic word for an electric fish, as mentioned in the previous chapter, is ra’ad, and it quite literally means lightning. It or a form of it can be found in Golden Age writings from the Middle East that deal with torpedoes and electric catfishes. Further, Englebert Kaempfer (1651–1716), a German scholar who served the Swedish government in Persia from 1684 to 1688, wrote the following about the discharges of the mottled torpedo ray (Torpedo panthera): “So powerful and so swift is the force of the horrifying exhalation that like a cold bolt of lightning it shoots through the handler.”24 Nevertheless, Kaempfer was not stating that the fish discharge and lightning are the same, and he does not use the word electricity anywhere in this context. Rather, he is only making an analogy, since the fish discharge and lightning share some common features, such as speed and the ability to cause pain. Importantly, neither he nor anyone else at this time had seen these fish give off a flash of light, the signature feature of lightning, nor had anyone detected even the faintest sound, the signature feature of the accompanying thunder. In 1746, Robert Turner, whose ideas we discussed in the previous chapter, went farther than Kaempfer by suggesting that the torpedo is electrical, although he could not back up his assertion with direct experimentation on these rays (hence, his use of electrified flounders). Three years later, however, there was a brief though far more significant report by Dale Ingram (1710–1793) in a lessthan-mainstream publication, The Student; or, The Oxford Monthly Miscellany.25 Ingram had lived in Surinam before he returned to England, and he too used the word “lightning,” this time to refer to the dangerous eel-like creature found in Surinam’s warm, sluggish, and murky rivers. In his 1750 article, he tells us: “Immediately to my great surprise and confusion and, as quick as lightning, my elbow received such a strong repelling force accompanied with such anguish that I thought my fore arm would have fallen off.”26

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Electric Fishes and the Path to Animal Electricity Ingram looked for movements at the time of discharge, a key feature of the mechanical theories, including Réaumur’s thinking about torpedoes, and he also wanted to know whether direct contact is necessary for the effect. He explained that “the fish never stirr’d, and my finger was scarce within an inch of touching him,” when a strong shock was felt.27 He added that the discharge could be conveyed through iron but not through a “common stick.” As for the word “electric,” we find it used in this context in his article. He writes: “On enquiring what was the method used in taking these animals, I was told that the Indians, as soon as they discover where they are, immediately seize them by their back and grasp them with great force, which defeats all their electric energy or spring.”28 In German translations of Ingram’s article, the somewhat ambiguous phrase “electric energy or spring” became elektrischer Kraft und Wirkung, meaning “electric force and effect.” This rewording strengthened the impression that Ingram had been contending that the shocks are, in fact, electrical.29 One year after Ingram’s article appeared, Michel Adanson (1727–1806), a French traveler and naturalist, had the opportunity to study a poisson trembleur (“tremble fish”) in Africa. Adanson lived in Senegal from 1749 to 1753, and his description of a fish found in this country’s rivers dates from 1751. He did not, however, publish his Histoire Naturelle du Sénégal until 1757.30 Hence, whether he knew what Ingram had written when he conducted his own experiments is questionable, although he would have had some time to find out prior to publishing his book. In any case, he does not cite Ingram. What is clear is that Adanson had already experienced shocks from a Leyden jar when he encountered the river fish, which is also described in the 1759 English edition of his natural history of Senegal.31 This edition, however, is less than faithful to the original in that it does not mention the fish’s telltale barbels! This omission seems to have confused many English readers at this time, including John Pringle of the Royal Society of London, who thought that Adanson was describing an electric eel, like those found in equatorial South America, not an electric catfish! Adanson’s fish had to be an electric catfish, for three reasons: (a) he does not refer to it as a ray; (b) there is no other kind of African river fish that can shock, and (c) he wrote in French that it had barbels near its mouth. During the 1600s, Portuguese missionaries in and near Ethiopia had “rediscovered” these catfishes, mentioned in important Middle Eastern writings but virtually unknown in the West, as had sailors and traders eager to discover Africa’s riches.32 Adanson was familiar with the Leyden jar and he was able to make a direct comparison between his (cat)fish and the electrical instrument, noting:

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Electric Fishes and the Path to Animal Electricity This effect did not appear to differ sensibly from the electrical motion of the Leyden experiment, which I had felt several times: and it is communicated in the same manner by simple contact, with a stock or iron rod five or six feet long; so as to make you instantly drop whatever you hold (p.227) in your hand. I have tried this experiment several times.33

Dutch natural philosophers in South America now began to study the electric eel, guided by scholars at home, what they were learning from correspondents in their Guiana colonies, their own experiences with the Leyden jar, and new (in some cases Dutch) contributions to the physics of electricity.34 One such person was Laurens Storm van 's Gravesande (1704–1775), a territorial governor with an interest in the natural world and a Figure 14.5: Jean Nicolas Sébastien “good friend” of Jean Allamand (1731–1787), the Dutch Allamand (Fig. 14.5), who physicist who communicated with had co-discovered the Laurens Storm van 's Gravesande (1704– Leyden jar and studied 1775), a Dutch governor in Guiana, about electricity with van the possibility of eel electricity. Musschenbroek (see Chapter 13). Wanting to know more about the powerful eels, Allamand had asked the governor of one of the Dutch colonies in the Guianas for additional information, and his erudite correspondent more than complied.

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Electric Fishes and the Path to Animal Electricity In a letter written in 1754, Laurens Storm van 's Gravesande told Allamand that the sidder-vis (Dutch for tremble fish) “produces the same effect as the electricity that I felt with you, while holding in a hand a bottle [Leyden jar] that was connected to an electrified tube by an iron wire.”35 The major difference, he added, is that the Gymnotus does not give off sparks. Moreover, and in parallel with what was being found in medical electricity experiments, the sidder-vis shocks seem to have the ability to cure “gouty pains.” Although this was pretty good evidence for the eels being electrical, Allamand was careful not to offend his friend Réaumur and his French associates, writing only that further tests and dissections should help to clarify the picture, especially with regard to how this new information might relate to sea torpedoes. Laurens Storm van 's Gravesande also corresponded with other natural philosophers, including Laurens Theodor Gronov (Gronow, Gronovius; 1730– 1777), a Dutch collector who also wanted to know more about the eels (he had a dead specimen in his personal museum). Gronov initially raised 25 questions about this South American fish and electricity, and his publications also supported the nascent idea that their shocks are electrical (he opined that the electricity probably streams forth from the numerous openings on the fish’s body).36 A few years later, Gronov was even more convinced that the eel possesses an electrical force (vim electricam), and he boldly extended this thought to the torpedo too.37 Frans van der Lott, a surgeon in the Dutch colony of Essequibo, published an especially interesting paper in 1762 in the same Dutch journal that had contained the earlier article on the shocking eel under Allamand’s name.38 He wrote from South America that its discharges can pass through conductors of electricity but not non-conductors, are extremely fast, and could even be felt by five people holding hands so as to form a human chain (this being reminiscent of some of Abbé Nollet’s Leyden jar demonstrations; see previous chapter). With regard to medicine, the fish is also like a Leyden jar, curing fevers, headaches, paralyses, and other nervous disorders. Remarkably, even crippled chickens with cramped legs benefited from the shocks in the experiments he described, which indicated that the human cures could not be quickly dismissed as due to suggestion and tricks being played by a patient’s receptive mind.

Changing Opinions The Allamand, Gronov, and Van der Lott publications were translated into several languages and the Dutch findings were widely disseminated in these translations, briefer synopses, and various secondary sources.39 In addition, the earlier short paper on the eel by Dale Ingram also circulated. (p.228) As can be imagined, these publications had the effect of converting some of the people strongly opposed to animal electricity into somewhat bewildered agnostics, while making some of the agnostics more into true believers.

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Electric Fishes and the Path to Animal Electricity This impact brings us back to Albrecht von Haller, whose ideas about the nerves were discussed in Chapter 12. Like his mentor Herman Boerhaave, he had rejected the idea of animal electricity, although he knew that electricity could travel extremely fast, a physiological requirement of great significance. He wrote that electrical matter is, in fact, a very powerful stimulus and one “fit for motion.” But he foresaw two major problems with associating electricity and animal physiology, problems that would lead him to opine that the animal spirits “are not of the nature of an electrical torrent.” The first was theoretical, and was based on the belief that electricity is not “confinable within the nerves, since it penetrates throughout the whole animal to which it is communicated, exerting its force upon the flesh and fat, as well as upon the nerves.”40 His second reason was experimental, the issue being that “a ligature on the nerve takes away sense and motion, but cannot stop the motion of a torrent of electrical matter.”41 Having been trained in Leiden, Haller was especially interested in following what was being published on the South American eel by Dutch scientists, who wrote in Dutch and Latin, as well as how some of these developments were being presented in German. Needless to say, his large network of scientific correspondents in the Netherlands and elsewhere also helped keep him up to date on the latest physiological discoveries. Although these findings did not lead him to become a champion of animal electricity during the 1760s, this possibility looked more and more real to him, because newer experimental findings by men skilled in science supported it. To appreciate how Haller’s mind was changing, one might look at different editions of his Elementa physiologiae. At first, he favored Réaumur’s mechanical theory about rapid falciform muscle movements accounting for the eel’s shocks. But by 1766, we find him writing, “I admit, after the recent experiments made on the anguilla stuporifera [numbing eel], that without doubts it rather seems that an electric vapour comes out from the animal.”42 Clearly, the eel experiments more than opened his eyes to the possibility of animal electricity, which would in turn make him more receptive to what he had once called the speculative and absurd idea of nerve electricity. In the 1767 edition of Haller’s Primae lineae physiologiae, which Edinburgh physician William Cullen (1710–1790) translated into English in 1786, there is an interesting footnote written by H. A. Wrisberg (1739–1808).43 Readers are reminded that there is still no more important physiological question than, “How do the nerves act in the bodies of animals?” And in this same footnote, we read that “Since 1766, I have been inclined to think, that it [the nervous fluid] perhaps resembles the electric and magnetical fluids.”44

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Electric Fishes and the Path to Animal Electricity Haller seemed to recognize that he could no longer abruptly dismiss the possibility of animal electricity because electrical matter could not be contained in the nerves and muscles, or, for that matter, because of the findings in ligature experiments. This is because newer observations, notably on the electric eel, were suggesting that, in some unknown way, what appeared to be an electrical fluid could be contained so that it would not harm the organism, and that his problematic ligature findings might be explainable in other ways. Haller’s wording in the text and the accompanying footnotes in his books are important because he was a towering figure in medicine and the leading physiology textbook writer at this time, a man whose books had a large readership. As we shall see later in this chapter, during the 1770s he would learn about the eel’s ability to generate a spark, which would be even stronger empirical evidence for what he had once dubbed the “repulsive” idea of animal electricity.

The Torpedo and the Royal Society Even when the eel was on its way to becoming electrical, at least in the eyes of some natural philosophers, the idea that the torpedo must also be electrical was far from resolved in 1766. In part, this was because many scientists during the Enlightenment had become reluctant to generalize from the data at hand. They knew that there was a need for comparable physiological studies on the torpedo, in addition to a need for comparative anatomical studies. Members of the Royal Society of London would play the leading role in these domains, stimulated by what the Dutch had done, but also by the observations of an American: physician, surgeon, and writer Edward Bancroft (1744–1820). Biographical information about much of Edward Bancroft’s life is scanty, but we know he was born in Massachusetts and raised and educated in Connecticut after his father died.45 While still a teenager, he started a medical apprenticeship in Connecticut, there being no medical schools in British North America at the time. But in 1763, he abruptly left for Barbados and then for Guiana, a term derived from the Arawak Indian words wai ana, meaning “(land of) many waters.” At this time, the Dutch territories in this region were growing rapidly in population and, with their sugar and coffee plantations, in economic importance. Despite still being in his teens and having had limited training, he had no difficulty finding employment as a plantation physician-surgeon on the banks of the Demerara River. Importantly, he used his spare time to collect information for a book he hoped to write about the region. This book took the form of a set of letters to his brother about the plants, animals, and human inhabitants of the region. These letters were edited and published in 1769 as An Essay on the Natural History of Guiana in South America, (p.229)

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Electric Fishes and the Path to Animal Electricity after he had been in London for 2 years (Fig. 14.6).46 It included 12 pages about the powerful river eel.

Bancroft made the strongest case yet for eel electricity, writing that it “Communicates a shock perfectly resembling that of Electricity.”47 He backed up his statement with a series of experiments, some comparing what happened when he put various conductors and nonconductors in the circuit, others on the ability of the fish to shock through lines, water, and even air, and still others on its ability to communicate “a violent shock to ten or a dozen persons thus joining hands, in a manner exactly similar to that of an electric machine.”48 He was cautious, however, when it came to presenting medical cures using a live eel as evidence for its electricity, and he even stated that what Van der Lott had written was greatly exaggerated. Some of his language when it came to eel therapeutics was very much like the wording Franklin had used in his report on Leyden jars not

Figure 14.6: The title page of Edward Bancroft’s 1769 Essay on the Natural History of Guiana.

curing humans of their longstanding palsies.49 Given Bancroft’s closeness to Franklin in London, he might have been influenced by him. It is also possible that he was trying to win his favor with his skepticism about medical electricity, even if from a fish. Franklin, as we have noted, had found that machinegenerated electricity probably had some uses (e.g., with hysterics) but was hardly a panacea.

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Electric Fishes and the Path to Animal Electricity Bancroft was absolutely certain that the eel could not be numbing or what some were calling torpifying in a mechanical way. Rather, “it is apparent, that the shock is produced by an emission of torporific, or electrical particles,” he wrote.50 And although he did not study sea torpedoes, he was convinced from what he had read about them that they must do the same. In this context, he took aim at Réaumur’s popular mechanical theory, putting all diplomacy by the wayside and calling it a mistake and a deception. Unfortunately, he explained, the Frenchman “has amused the world with an imaginary hypothesis.”51 These very words were repeated in various reviews of his book that were read around the world, and they registered on Franklin, who was very influential at the Royal Society and was now eager to learn about animal electricity, something he had not investigated in Philadelphia or now from his base in London. One of us (S.F.) could find no evidence to suggest that Bancroft continued to study electric fishes after he arrived in London. But Franklin and a rather unknown but aspiring natural philosopher, who associated with Franklin and was a part of his circle at the Royal Society, contacted Bancroft on several occasions to discuss fish electricity. The younger man was John Walsh (1726– 1795). Colonel John Walsh was born in India in 1726.52 He was related to MajorGeneral Robert Clive (1725–1774) and served as his secretary in Bengal from 1757 to 1759. He was also related to Neville Maskelyne (1782–1811), the Astronomer Royal, who along with Franklin (and four others) had sponsored Edward Bancroft for membership in the Royal Society. Walsh had amassed his fortune before he left India for England, where he secured a seat in the House of Commons in 1761 that he would hold for 19 years. He was elected into the Royal Society in 1770, being “a Gentleman well acquainted with philosophical & polite literature, & particularly versed in the natural history and antiquities of India.” Probably at Franklin’s urging, and assuredly with his blessing, Walsh traveled to La Rochelle in 1772 to conduct a (p.230) series of electrical experiments on the torpedoes common to the region, torpedoes that had previously been studied by Monsieur Réaumur, who had been born there. Franklin had worked with Walsh in designing the needed electrical experiments, many of which followed from what Bancroft had done with his eels and what the Dutch had done with their eels a bit earlier. Walsh described his findings in a journal, as well as in letters that he sent back to Franklin. These were then constructed into an article published in 1773 in the Philosophical Transactions of the Royal Society of London and also in a pamphlet (Fig. 14.7).53

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Electric Fishes and the Path to Animal Electricity Not all of Walsh’s findings favored torpedo electricity. For example, he could not detect their electricity with his electrometers and, like Bancroft with the electric eel, he never witnessed miniature thunder and lightning shows. But in other ways he extended what had been reported with the eel to his smaller and less powerful French torpedoes. These findings allowed him to register upbeat entries in his journal of experiments, such as: “All the Experiments this morning strongly marked the effect to be Electrical, and not arising from a muscular stroke, nor from a refrigidating [sic] quality in the animal, of which it has nothing.”54 Walsh might have been the first person to employ the term “electric organs” when alluding to the structures behind the discharges. He might also have been the first person, or at least one of the first, to use the phrase “animal electricity.” After Walsh returned to London, he involved physicist Henry Cavendish (1731– 1810) in his research program, hoping to understand how the torpedo’s discharge could stun a fish some distance away. Cavendish rose to the occasion and even made artificial torpedoes using Leyden jars (Fig. 14.8). These models and his many calculations helped him to explain everything that Walsh had observed in La Rochelle, both positively and negatively, including why his electrometers did not pick up the discharge (it was too rapid) and why there was no observable sparking (e.g., the discharge had insufficient “spring”).55 “On the whole,” explained the eccentric English physicist, “I think, there seems nothing in the phenomena of the torpedo at all incompatible with electricity.”56 Additionally, Walsh provided anatomist John Hunter (1728–1793) with some dead torpedoes for dissection. Mr. Hunter, the younger brother of Dr. William Hunter (1718–1783), was one of the most important, and certainly one of the most fascinating, medical and scientific figures of the Enlightenment57 (Fig. 14.9). Although he grew up on a farm in Scotland and lacked a university education (hence “Mr.”), once he arrived in London to help his more erudite brother William at his private school of anatomy, he cut, probed, and preserved everything he could lay his hands on with consummate skill. Feared and accused by some of being

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Electric Fishes and the Path to Animal Electricity a “resurrectionist” (grave robber), he is today regarded as a founder of modern “scientific surgery” because of his physiological and experimental approaches to surgical problems. To say the least, he has also been praised for the remarkable collections he put together for research and teaching purposes, parts of which can still be seen in London today.

In 1773, Hunter provided the best verbal and pictorial descriptions of the torpedo’s electrical organs to date (Fig. 14.10).58 He wrote that they are made of about 470 perpendicular columns comprised of “either Hexagons or irregular Pentagons” separated by thin membranes. The many nerve branches innervating these structures also impressed him. He thought the nerves could, in his words, be “subservient to the formation, collection, and management of the electric

Figure 14.7: John Walsh’s torpedo publication was published as if it were just a letter to Franklin, who helped him plan his torpedo experiments and present this material. It actually contained two of Walsh’s letters to Franklin, a letter from the Mayor of La Rochelle, the French coastal town in which the research took place, and extensive commentary.

fluid.”59

The Coveted Spark In 1774, when Walsh won the Copley Medal for his research on torpedo electricity, he knew that the case being made for specialized fish electricity was still not as strong as it could be. In particular, there was still an intense need to see a spark at the time of an electric fish discharge. Because Henry Cavendish was suggesting that this might not be possible with small saltwater torpedoes, his attention, as well (p.231)

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Electric Fishes and the Path to Animal Electricity as that of other members of the Royal Society, shifted over to the far more powerful South American eel.

The problem the ambitious eel researchers faced was to a large extent a practical one. The eels bruised easily and required warm temperatures. Their demands made them poor travelers for long voyages from South America to European or even North American centers of learning, where groups of skilled individuals wanted to study them while they were still alive.

Figure 14.8: An illustration from Henry Cavendish’s 1776 article on the physics of the torpedo’s discharge. Using artificial torpedoes constructed with multiple Leyden jars, what had been learned from

Walsh about real torpedoes, and The first eel to survive a journey mathematics, Cavendish was able to show far to the north of the how the electric current could spread sweltering South American from the fish and explain why there was jungles made it to Philadelphia no visible spark. during the summer of 1773. It was studied by some members of the American Philosophical Society, the organization co-founded by Benjamin Franklin, who was at the time still in London. The individuals involved with studying this eel basically confirmed what had been shown in earlier on-site studies, with one major exception. Hugh Williamson (1735–1819) reported that the discharge could jump a gap in a wire.60 Although there was no visible spark, he personally felt the shocks, which “doubtless leaped from the point of one wire to the other,” and opined that a spark might even have been seen had the eel been in better health. This finding, he and his American associates knew, was strongly indicative of an electrical discharge. When Williamson visited London in 1774, he met with Franklin, Walsh, and Hunter, all of whom shared his great interest in fish electricity.61 Soon afterward, he submitted his material to the Royal Society for publication in its Philosophical Transactions, where it appeared in 1775.62 In 1774, five eels made it to Charleston, South Carolina, where Alexander Garden (1730–1791), a Scottish immigrant physician, naturalist, and disciple of Linnaeus, left his sickbed to study them.63 Garden’s physical descriptions of the eels, published in the Philosophical Transactions in 1775,

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Electric Fishes and the Path to Animal Electricity (p.232) were exceptionally detailed, but his experiments only confirmed what had been found previously, adding little that was new and exciting.

When Garden learned that Captain George Baker (fl. 1770s), who transported the eels from South America and owned them, hoped to take them to London after leaving South Carolina, he was skeptical about their ability to survive and told Baker so. He also advised him on how to preserve their dead bodies in alcoholic spirits, and told him who should receive them, should they die in transport. As Baker anticipated, none made it to London alive. But all was not lost. After the dead eels arrived in London, John Walsh purchased them. He then provided John Hunter, who had previously dissected several of his torpedoes, with some specimens to dissect. Hunter’s findings, once again accompanied by magnificent drawings of the electrical organs (structured like those of the torpedo, but with the columns now arranged front to back rather than top to

Figure 14.9: John Hunter (1728–1793), the most skilled anatomist of the day, who dissected some of Walsh’s torpedos, and who later also dissected and illustrated the eel’s electric organs and nerve supplies.

bottom), were also published in the 1775 Philosophical Transactions.64 Figure 14.10: Some of John Hunter’s (1775) exceptional illustrations of the torpedo’s electrical organs.

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Electric Fishes and the Path to Animal Electricity Receiving these specimens generated even greater interest in getting some live eels to London. A subscription was launched to help finance Captain Baker, who, to the delight of his supporters, successfully transported some live eels to London in 1776. It was with one of these eels that Walsh was able to obtain his coveted spark in darkness on November 1, 1776.65 Walsh went on to repeat his demonstration before his Royal Society colleagues and others. Unfortunately, his mentor Franklin never saw him draw a spark: Franklin had recently sailed back to America, knowing that there would now be a war for American independence. Oddly, Walsh did not write up his greatest scientific triumph. Nor did Gentleman’s Magazine cover it, even though this widely read periodical had included synopses of some of the earlier events in the history of fish electricity, particularly those reported to the Royal Society of London.66 But what Walsh did was no secret, in part because what he accomplished was spread in other ways: by word of mouth, via letters to other scientists, and in publications undertaken by others. Haller, for one, soon became aware of this “hurdle” being cleared. John Pringle (1707–1782), Franklin’s friend and now President of the Royal Society, was among Haller’s numerous correspondents in Europe (Fig. 14.11). In 1774, he had informed Haller about Walsh’s experiments on the French torpedoes, “by which you’ll find the opinion of Musschenbroek confirmed, with regard to the stupefying quality of that animal proceeding from electrical matter.”67 On August 27, 1776, a year after writing his historical discourse on the torpedo in honor of Walsh receiving the Copley Medal for his research,68 Pringle described to Haller how “a common English sailor” [a reference to Captain Baker] had brought some live eels to London. Pringle informed Haller that he “had the satisfaction of receiving a sensible shock, in the circle made by 5 or 6 of us,” adding: A tolerably well charged Leyden bottle could not have behaved better. Next day Mr Walsh went alone & with a proper apparatus was sensible of a spark crossing the intersection of a strip of tin foil…an electrical feat which (p.233)

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Electric Fishes and the Path to Animal Electricity he had never been able to obtain from the torpedo. But he has not been able to repeat the experiment; on account of the weakness of his eel, which he purchased from the importer. But whether he verifys [sic] by that test or not the identity of the electrical matter, & that with which these fishes are actuated, the best electricians here are satisfied, that there is not so much as a specific difference between them.69

In mid-December, Pringle sent Haller another letter on the subject, writing: I have forgot whether I mentioned Mr Walsh’s having drawn sparks of fire from those animals [eels]. He has, & I am one of the numerous witnesses of that curious circumstance. In your new edition of the Physiology you may safely assert it. The sparks were vivid & repeated, & were seen,

Figure 14.11: John Pringle (1707–1782), President of the Royal Society of London, who was very interested in fish electricity and even wrote a treatise on it when awarding John Walsh the Copley Medal in 1775 for his research. Pringle kept Albrecht von Haller very well informed about the latest developments in this area, including Walsh’s spark experiments.

the last time I attended, by about 70 people at once.70 In a similar way, Jan Ingenhousz (1730–1799), another witness (and soon to be a discoverer of photosynthesis in plants), informed Franklin of what had transpired. This was in a letter dated November 15, 1776. Franklin was already quite convinced that fish, artificial, and atmospheric electricity are one and the same. But now he learned that there was even better support for this idea. “Mr. Walsh has at last found out the method of making an Electric spark visible from a Gymnotus of Surinam,” Ingenhousz wrote to his American friend, who was now in France hoping to secure support for the Americans fighting against the British.71 Franklin, as can easily be imagined, would have welcomed this news, even though he was focused on the war effort, which could account for why no letters have surfaced with his response to Ingenhousz or to congratulate Walsh. Page 25 of 31

Electric Fishes and the Path to Animal Electricity Wider audiences also learned about this landmark event in the history of animal electricity via a letter in the French scientific journal Observations sur la Physique,72 and through briefs that appeared in several London newspapers. Hence, on August 5 and 6, readers of the Gazetteer and New Daily Advertiser, the Public Advertiser, and the Morning Chronicle and London Advertiser were informed: On Thursday, the President and many Gentleman of the Royal Society were present at an exhibition of the effects of these extraordinary fish; and on Friday Mr. Walsh, whose Observations on the Electricity of the Torpedo have been published in the Philosophical Transactions, made some experiments on them, and obtained from the Gymnotus the electrical spark, which he never could procure from the torpedo; by which event an entire agreement in the natural effect of these animals, and the artificial effect of the Leyden phial, is established. The newspapers also covered a second big demonstration, which took place on November 15, 1776. Their reporters further mentioned that Captain Baker had taken an apartment in Piccadilly, where inquisitive men and women would have a chance to see these eels and even a demonstration of how they could spark— not for free, of course, but for an individual or a group rate. Thereafter, Baker, who was very much in it for the money, ran advertisements of his own.73 With the spark now being publicly demonstrated, individuals who had scoffed at the notion of fish electricity and were still holding out had to rethink their positions. Indeed, specialized fish electricity seemed to be the new reality, even if to many onlookers it seemed to make little intuitive sense. Nevertheless, some very important issues remained to be addressed. One was how any moist body could generate, build up, and distribute its electricity in a way that would not prove maladaptive. This issue, of course, related to how the electrical force could be confined to a fish’s electrical organs and associated nerves without diffusion through other moist tissues. Another was whether fish electricity is identical to that from electrical machines or the heavens, or whether there might be several electricities, with some differences, even if subtle, existing within the group. And a third issue, arguably the most perplexing of all, was whether other organisms, such as common frogs, beasts of burden, adorable (p.234) pets, and even humans cast in God’s image, might function by electricity, albeit not enough electricity to be felt or seen, but electricity nonetheless—and, needless to say, just how this might be demonstrated.

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Electric Fishes and the Path to Animal Electricity In our next chapter, we shall examine how the concept of specialized fish electricity would be generalized to other animals late in the 18th century, and how this development led to an epic battle between two giants in the history of the sciences. We shall also show that the evidence for the nerves of frogs and other animals being electrical left much to be desired in the opening decades of the 19th century. In short, the transition to a more modern electrical nerve and muscle physiology did not take place overnight. But with a growing understanding of electricity, a continuing transition away from older, looser ways of thinking about the nerves and muscles would take place, and the term “animal spirit” would fade out like a dying ember early in the new century. Notes:

(1) Norris, 2002; Nelson, 2006. (2) Humboldt and Bonpland, 1811 (French), 1852/1971 reprint (English). Humboldt’s vivid description of what these eels can do to men and pack animals can be found in Vol. 2, Ch. XVII, which corresponds to Ch. II (pp. 111–131) of the second volume in the English edition. (3) As noted in the previous chapter, an in-depth look at the history of how electric fishes were viewed, and how this related to physiology and medicine, can be found in Finger and Piccolino, 2011. This book contains many illustrations, extensive quotations, and primary-source references. (4) These drawings can be observed in the Tomb of Ti and the Tomb of the “Two Brothers” from Dynasty V (from about 4,400 years ago), and in the slightly newer tomb complex of Mereruka (Dynasty VI), all located in the necropolis of Saqqara near the ancient city of Memphis. (5) Westendorf, 1999. (6) Gamer-Wallert, 1970; Altenmüller, 1973. (7) Plato, 1892, p. 39, sect. 80. (8) Hippocrates, as mentioned in Chapter 1, was born on the island of Cos off the coast of modern Turkey in about 460 BCE and died in approximately 370 BCE. It is difficult if not impossible to determine which texts or fragments Hippocrates wrote and which came from his followers and students. Collectively these texts, all of which take the supernatural out of medicine, are referred to as the Corpus Hippocraticum, and many deal with regimens or diets for maintaining or restoring eucrasia or good health. The torpedo is presented as an easily digested, nutritious food in these works, much as is barley gruel, a favorite of these ancient physicians. (9) Aristotle, 1965, pp. 311–312. Page 27 of 31

Electric Fishes and the Path to Animal Electricity (10) Plutarch, 1957, XII, 978, p. 435; translation revised in Finger and Piccolino, 2011, p. 38. (11) Pliny the Elder, 1963 and 1983 editions. This thought appears in the introductory section to Book XXXII. (12) For example, Pliny writes that unwanted hair can be removed with the brain of the torpedo applied with alum on the 16th day of the moon (Book XXXII, Sect. 47), and that “if it is caught while the moon is in Libra and kept for three days in the open, it makes parturition easy every time afterwards that it is brought into the room” (Book XXXII, Sect. 36). (13) For details and thoughts on Galen and the torpedo’s powers, see Debru, 2006; Finger and Piccolino, 2011, pp. 49–52. (14) The description comes from Oppian, Halieutika, Book II, verses 56–85. This translation dates from the early 18th century (Oppian, 1722, pp. 64–65). (15) Copenhaver, 1991; Finger and Piccolino, 2011, pp. 65–159. (16) Kircher, 1667, p. 125. (17) Redi, 1671. (18) Ibid., pp. 53–54. (19) Lorenzini, 1678, 1705. For an English translation, see Guerrini, 1999. (20) Lorenzini, 1678, pp. 108–109. Since we now know there are no visible movements in the electric organs at the time of the shock, Lorenzini might have been misled by contractions of the hand touching the discharging fish, which in turn could have caused the fish itself to move. This chain of events, however, must be regarded as speculative, and other factors, such as random or semirandom movements, might also have entered the picture. (21) Borelli, 1680–81. (22) Wheeler, 1926; Grasse, 1962. (23) Réaumur, 1717. (24) Kaempfer, 1712; see Bowers and Carrubba, 1970, and Carrubba and Bowers, 1982, for English translations and useful commentary. (25) Ingram, 1750a. (26) Ibid., p. 50. (27) Ibid., p. 50. Page 28 of 31

Electric Fishes and the Path to Animal Electricity (28) Ibid., pp. 51–52. (29) Ingram, 1750b. See Finger and Piccolino, 2011, pp. 195–197, for more on Ingram and the translations of his brief article. (30) Adanson, 1757. The fish is described on p. 135 in this, the original French, edition. (31) The fish is described on pp. 244–145 of the 1759 English edition. (32) Piccolino, Finger, and Barbara, 2011. (33) Adanson, 1759, pp. 244–245. For the French, which is consistent with this translation, see Adanson 1757, p. 135. (34) Koehler, Finger, and Piccolino, 2009; Finger and Piccolino, 2011, pp. 201– 214. (35) Laurens Storm van ‘s Gravesande’s letter was published in an article in which Allamand added commentary and listed himself as the author (Allamand, 1756). This article has been translated from Dutch to English: see Koehler, Finger, and Piccolino, 2009, pp. 728–730, and Finger and Piccolino, 2011, pp. 202–204. (36) Gronov, 1758, 1760. He speculates on electricity flowing from the pores on p. 472 of his 1758 article, which appeared in a Dutch periodical. (37) Gronov, 1763. (38) Van der Lott, 1762. This letter is also translated in Koehler, Finger, and Piccolino, 2009, pp. 738–743, and in Finger and Piccolino, 2011, pp. 207–210. (39) For more on how the word spread and references to these secondary publications, see Koehler, Finger, and Piccolino, 2009, pp. 744–757, and Finger and Piccolino, 2011, pp. 211–214. (40) Haller, 1766/1786/1966 reprint, vol. 1, p. 221. (41) Ibid. (42) Haller, 1766, Tome VIII, p. 176. (43) Wrisberg’s role can be gleaned from the frontispiece. It is noted in Lester King’s introduction to the facsimile of this translated volume (p. xxxii). (44) Haller, 1767/1786/1986 reprint, p. 222.

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Electric Fishes and the Path to Animal Electricity (45) For more on Bancroft’s remarkable life and motives, including his ties to Franklin, his electric eel experiments, and his spying (he seems to have been a double agent, spying for both the British side and the rebellious Americans!), see Anderson and Anderson 1973, Finger, 2009, pp. 61–79, and Finger and Piccolino, 2011, pp. 217–229. (46) Bancroft, 1769. (47) Ibid., p. 192. (48) Ibid, p. 196. (49) Franklin, 1758; also see our previous chapter. (50) Bancroft, 1769, p. 198. (51) Ibid., p. 199. (52) For more on Walsh, his connections with Franklin, and his torpedo experiments, see Piccolino and Bresadola, 2002, Piccolino, 2003, and Finger and Piccolino, 2011, pp. 230–257. (53) Walsh, 1772, 1773. (54) Walsh, 1772, p. 29. He is here referring to the ancient theory, promoted by Galen, involving some sort of a cold venom. (55) Cavendish, 1776. (56) Ibid., p. 222. (57) There are many biographies of John Hunter, starting with Jessé Foote’s portrait of him in 1794, right after his death. Stephen Paget wrote a famous biography in 1898. For more recent biographies, see Kobler, 1960, Dobson, 1969, and Moore, 2005. Another valuable source of information about Hunter is the Case Books of John Hunter compiled by Allen et al., 1993. (58) Hunter, 1773. (59) Ibid., p. 487. (60) Williamson, 1775, p. 100. (61) Hosack, 1820, pp. 51–52. (62) Williamson, 1775.

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Electric Fishes and the Path to Animal Electricity (63) Garden, 1775. See Finger, 2010, pp. 269–280, for more on Garden as a naturalist and collector, and how Linnaeus inspired his scientific endeavors, including on the electric eel. (64) Hunter, 1775. (65) See Finger and Piccolino, 2011, pp. 281–286. (66) Finger and Ferguson, 2009. (67) Pringle to Haller, April 9, 1774, in Sonntag, 1999, p. 300. Van Musschenbroek discussed torpedinal electricity in his 1769 physics text, Cours de Physique Experimentale et Mathematique, Vol. 1. (68) Pringle, 1775. (69) Pringle to Haller August 27, 1776. Ibid., p. 346. (70) Pringle to Haller December 13, 1776. Ibid., pp. 348–349. (71) Willcox, 1983, p. 7. (72) Le Roy, 1776. (73) Extracts and references to a number of newspaper reports about Walsh’s two spark demonstrations, and Baker’s willingness to demonstrate (for a fee) some of the things that the eels could do, including the spark, can be found in Finger and Piccolino, 2011, pp. 292–297.

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From Fishes to Frogs and Nerve Electricity

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

From Fishes to Frogs and Nerve Electricity C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0015

Abstract and Keywords This chapter takes a look at efforts made in the study of the possibility that humans could create and store electricity, just like certain animals. It first introduces Luigi Galvani, who studied the possibility that like electric fishes, the nerves and muscles of barnyard animals, humans, and frogs work by electricity. It then studies some of the enduring features of the animal spirit paradigm and Alessandro Volta's critique of Galvani's study. It also looks at some of the new findings on electric fish experiments in Italy and the physiological advances in Germany. This chapter ends with a discussion on 20th-century developments on nerve electricity. Keywords:   nerve electricity, Luigi Galvani, electric fishes, animal spirit paradigm, Alessandro Volta, electric fish experiments, physiological advances

We believe, therefore, that the electric fluid is prepared by the activity of the cerebrum, that it is extracted in all probability from the blood, and that it enters the nerves…If this be the case, perhaps at last the nature of animal spirits, which has been hidden and vainly sought after for so long, will at last come out with clarity. Trans. from Luigi Galvani, 1791, p. 402

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From Fishes to Frogs and Nerve Electricity The importance of the three strongly electric fishes mentioned in the previous chapter in the history of neurophysiology cannot be overstated, because research on the electric eel, electric catfishes, and saltwater torpedoes showed that at least some animals really could be electrical. Nevertheless, the majority of late-18th-century natural philosophers were hesitant about making the jump from these strange fishes to other animals, especially humans. After all, no other animals shocked like these fishes, which could feel just like Leyden jars when they discharged. Moreover, these fishes were found to have identifiable electric organs made of elements stacked in columns or rows, which other animals lacked. Devoid of the unique electrical organs that John Hunter1 had so beautifully illustrated in his Philosophical Transactions articles on the torpedo and the eel (see Chapter 14), how could other organisms manufacture or store electricity? As a result of these mindsets and deeply ingrained perceptions, notions about non-electrical matter coursing through the nerves to the muscles, and from the peripheral sense organs to the brain, or in some other way utilizing the nervous system, continued to be entertained after John Walsh obtained his coveted spark in 1776. Nevertheless, the fish experiments and the electric Zeitgeist did lead some notable individuals to go beyond Walsh and write about a broader role for electricity in animal physiology, or what was sometimes called the “animal economy,” even though the “evidence” cited to support such theorizing was at first indirect, based on faulty experiments, derived with shaky logic. For example, during the 1780s Francesco Giuseppe Gardini (1740–1816), an Italian physician, and Pierre Bertholon (1741–1800), a French physicist, wrote about how a universal electric fluid permeates the atmosphere around us, penetrates our pores, and can affect or act on our bodies.2 These men also postulated that basic bodily processes, such as blood flowing against vessel walls, might produce this intrinsic electricity by friction, somewhat like an electric machine. In his discourse, Bertholon mentioned how women would become unusually nervous on very dry days and during thunderstorms, times characterized by intense atmospheric electricity, and how sparks quite literally might fly during sexual intercourse! As might be expected, others demanding better evidence assailed and snickered at this sort of loose reasoning, including accomplished physicist Alessandro Volta (1745–1827), who in 1782 could not believe that merely rubbing a cat’s fur was being accepted in some circles as evidence for intrinsic animal electricity.3

Galvani and Animal Electricity In 1791, Luigi Galvani (1737–1798), a Bolognese man of medicine and dedicated scientist, presented the results of years of physiological experiments.4 His thesis, which he believed he supported with ample experimentation, was that the nerves and muscles work by electricity in frogs, barnyard animals, and even humans, just as they do in electric fishes. Page 2 of 35

From Fishes to Frogs and Nerve Electricity There have been numerous biographies of Galvani (Fig. 15.1), some more accurate than others.5 Born into a middle-class family in Bologna in 1737, and often depicted as even-tempered, modest, and moral, he also had ambition and was driven to make something of himself. After graduating from the University of Bologna in 1759, he worked at various hospitals as an assistant surgeon while also pursuing his scientific studies. In various ways, he developed important (p. 236) interdisciplinary skills and an approach to science that combined rigorous experimentation with deep reasoning.

Prior to writing about animal electricity, he had studied the urinary and auditory systems of birds, presented a since-lost memoir on Haller’s concept of irritability (in 1772), and investigated other scientific issues and problems. His hard work and dedication to science and medicine earned him the rank of professor at the University of Bologna, membership in the Istituto delle Scienze, and the title of the chief physician at the Collegio medico. Galvani’s treatise on animal electricity bore the title De viribus electricitatis in motu

Figure 15.1: Luigi Galvani (1737–1798), who argued for animal electricity in his De viribus electricitatis in motu musculari commentarius of 1791 and then in additional experiments.

musculari, Commentarius and has become a classic in physiology.6 It was written in Latin and published in 1791 in the Commentarii of the Accademia delle Scienze of Bologna. In contrast to other, looser speculations about the frog’s and other animals’ electricity at this time, it was based on a program of experiments and critical thinking that extended over an 11-year period. Yet the picture Galvani paints in this text deviates in significant ways from his laboratory notes.7 His notes and letters more accurately reveal the course of his experiments and how he pondered and changed his thoughts on a number of occasions, as he collected data at his laboratory and at his home, where he also had electrical equipment and focused on the bigger picture.

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From Fishes to Frogs and Nerve Electricity As pointed out by Finger and Piccolino in their book on electric fishes in the history of physiology,8 what Walsh and others had demonstrated with electric fishes served as the basis for Galvani’s frog electricity experiments, which began in Bologna around 1780. The Dutch and then the British fish experiments were well known among natural philosophers in Italy, thanks to word of mouth, original language publications, and various translations, synopses, and publications in Italian.9 Some of these communications were, in fact, a part of Galvani’s personal library.10 Also of significance and not to be overlooked, Haller’s concept of irritability and the notion of animal electricity had been the subjects of ongoing debates in Bologna. Marc’Antonio Caldani (1758–1794) and Felice Fontana (1730–1805), for example, had been among the staunchest supporters of Haller’s irritability theory, and Tomaso Laghi (1709–1764) had been an early advocate of giving internal electricity a central role in muscle contraction.11 These were not, however, the only factors to draw Galvani into conducting his nerve and muscle physiological experiments: his interests in medical electricity and the scientific and medical culture in Bologna were also important, as were his love of science and genuine inquisitiveness. Galvani’s work was largely carried out on “prepared frogs,” meaning frog muscles and nerves cut off from the brain, and sometimes the spinal cord too, so as to preclude the roles of sensations and voluntary muscular contractions (Fig. 15.2). His first experiments in this domain were on the effects of nerve ligatures, the ability of nerves to transmit electricity, and how muscular responses might be obtained with weak external electrical stimuli. Albrecht von Haller had found that ligatures could diminish nerve function, and knowing that electricity could still flow past a constriction, Haller believed that this finding argued against the nerves being electrical.12 Galvani’s mind seemed to be focused primarily on the fact that external electricity could be a powerful nerve stimulant when he started in 1780, but this was to change early in 1781. Galvani’s change in thinking occurred after he observed that a frog muscle contracted when a spark was thrown from an electrical machine not directly connected to his preparation.13 Subsequent experiments showed that all that was needed was for somebody to touch his preparation with a conductor of electricity (e.g., metal, a finger) at the moment when a spark flew from the distant electric machine. Further, the effects were far greater when it was a nerve, as opposed to a muscle, that was touched. This finding cast doubt on Haller’s doctrine, which held that the basis of the (p.237)

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From Fishes to Frogs and Nerve Electricity contraction is intrinsic to the muscles. As he continued his experiments with different circuits, Galvani now began to think that the external electricity only serves to activate an internal force in the nerves, an inner fluid basic to muscle contractions. The observation that his preparations could fatigue with repetitive stimulation and then recover if left alone further suggested that the contractions he was witnessing might be due to the activation of such an internal agent.

Between 1783 and 1786, Galvani conducted numerous physiochemical experiments. Some led him to deduce that

Figure 15.2: Some of Galvani’s instruments, including a frictional machine for generating electricity and Leyden jars. Note the prepared frog on the left and others on the laboratory table. (From Galvani, 1791)

the nerves probably contain an abundant amount of oily matter. This thought led him to view the nerves as having a central conductive core that is covered with insulating material. He wrote that “nerves are hollow in their internal part, or at least made up of matter fit for the passage of electric fluid, and exteriorly [are made up] of an oily substance or of another matter capable of hindering the passage and the dispersion of the electric fluid, which flows inside them.”14 This extremely important revelation allowed him to understand how electricity could be contained in, or confined to, specific parts of a moist body without causing physiological chaos. This had been one of Haller’s major objections to the concept of animal electricity. In Galvani’s 1791 De viribus, he organized his experimental results into three parts: artificial, atmospheric, and animal electricity. The latter program of experiments, he writes, began in 1786, after he had inserted a metal hook in a frog’s spinal cord and suspended it from the iron fence of his balcony on a clear day, hoping to determine if weak atmospheric electricity could stimulate contractions. Nothing happened until he (or his nephew Camillo) moved the preparation so the hook touched the railing. This small manipulation led to replicable contractions that Galvani and those helping him found could also be obtained with various metals indoors. Not recognizing that the different metals involved could serve as an external source of electricity (Volta would get the credit for this insight), these experiments led him to postulate the presence “of a flow of an extremely tenuous nervous fluid…similar to the electric circuit which develops in a Leyden jar”—in other words, an electrical fluid that could flow within an insulated nerve core to specific muscles.15

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From Fishes to Frogs and Nerve Electricity With frogs not having electrical organs like the specialized fishes, however, Galvani faced a dilemma when it came to identifying the sites of the “double and opposite,” or positive and negative, animal electricity. This was a fundamental issue, one critical for thinking about how electricity could flow from one place to another. Although he thought one site must be in the nerve and the other in the muscle, he could not quite grasp how an electrical difference could exist and be maintained between two different parts of these connected and moist conductive elements. His thought process led him to consider the stone tourmaline, which has electrical properties that are maintained (p.238) even when it is broken into smaller pieces.16 Nevertheless, he discarded the tourmaline model upon further thought and reconsidered the Leyden jar analogy, which had never been far from his mind. Historically, as discussed in Chapter 14, not only did earlier researchers (e.g., Allamand, Van der Lott, Adanson) emphasize that the fish discharges felt like those from Leyden jars, but John Walsh had alluded to biological Leyden jars when discussing his torpedo research.17 Moreover, as Galvani would have known, physicist Henry Cavendish’s working models of the torpedo, which allowed him to explain various features of their shocks, utilized a collection of Leyden jars.18 Finding more vigorous contractions when he wrapped muscles in thin sheets of metal (akin to the foil covering a Leyden jar) markedly affected Galvani’s thinking about biological Leyden jars in 1786 and 1787. And with his biological Leyden jar model, Galvani constructed a new neuromuscular physiology, one consonant with the notion that the nerves and muscles work by electricity generated from the brain. He would begin Part IV of his landmark treatise, the part dealing with conjectures and conclusions, with these words: From the things that I have ascertained and investigated thus far, I believe it has been sufficiently well established that there is present in animals an electricity which we, together with Bartholonius and others are wont to designate with the general term, “animal.” This electricity is present, if not in all, at least in many parts of animals. It is seen most clearly, however, in the muscles and nerves.19

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From Fishes to Frogs and Nerve Electricity Galvani’s interest in medicine never waned, and his implications for medicine followed in this fourth part of his treatise. Interestingly, these paragraphs still reflected the older thought that some neurological disorders stem from blockages in the nerve tubes. But while tied to the past with this idea, he also broke from the past by maintaining that these blockages involve “nerveo-electric fluid flowing from either the muscle to the nerve or from the nerve to the muscle.” With regard to therapies in these conditions, he advised trying medical electricity, since external electricity might be able to overcome at least some of the blockages and could, in theory, increase the strength of the weak animal electricity.20 He also tied epilepsy to animal electricity, envisioning that it could “flood either from the muscles or other parts through the nerves to the cerebrum” in some pathological conditions.21

Enduring Features of the Animal Spirit Paradigm At this juncture, we can ask whether Galvani was abandoning the animal spirit paradigm or just trying to modify it. In reading the conjectures in the fourth part of his 1791 treatise, we see that he was never claiming that his research has finally put an end to the animal spirit doctrine. To the contrary, the feeling he conveys is that his great achievement is the discovery of the true nature of the previously elusive spirit, which in his mind still runs from the brain through the nerves to activate the muscles, much as had been the case in earlier, nonelectrical formulations of the venerable doctrine. After pointing out why animal electricity is no different from what others had been calling genuine electricity, and that electric fishes differ from other animals only by producing a greater abundance of electricity that can be discharged at will, he writes that the source of the electricity is probably “identical with that indicated by the physiologists as being the source of animal spirits, namely the cerebrum.”22 There is nothing here to suggest that he is thinking that the electricity might be originating from the muscles and/or the nerves, even if he might have been pondering this possibility. Several paragraphs later, he summarizes the various parts of his electrical thesis and, in effect, incorporates it into the existing framework that has long characterized the animal spirit paradigm. In translation: We believe, therefore, that the electric fluid is prepared by the activity of the cerebrum, that it is extracted in all probability from the blood, and that it enters the nerves and circulates within them in the event that they are hollow and empty, or, as seems more likely, they are carriers for a very fine lymph or other similarly subtle fluid coming from the cortical substance of the brain, as many believe. If this be the case, perhaps at last the nature of animal spirits, which has been hidden and vainly sought after for so long will at last come out with clarity.23

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From Fishes to Frogs and Nerve Electricity Many of the finer details of Galvani’s thinking would, of course, fall by the wayside. In particular, his idea that the electricity likely stems from the brain, is passively transported by the nerves, and builds up in the muscles would not withstand the test of time. In contrast, his thought that the nerves and muscles are electrical in far more than just a few electric fishes would replace earlier, non-electrical notions about nerve and muscle physiology following considerably more research. This positive development, however, would not obtain broad acceptance during the 7 years remaining in Galvani’s life—years that had to be extremely stressful for him. First, shortly before his De viribus went to press, his beloved wife Lucia died.24 Further, just prior to his own death in 1798, he lost his appointments and affiliations because he refused to swear allegiance to the Cisalpine Republic created by Napoleon Bonaparte (1761–1821), who wished to exert more influence over this region of Italy. And making matters worse, the experimental support for his theory was assailed and attacked, and this started very shortly after his De viribus began to circulate. Galvani had been optimistic about having finally solved one of nature’s greatest mysteries. He rather naïvely had written: “after our experiments, certainly nobody would, (p.239) in my opinion, cast doubt on the electric nature of such spirits.”25 He did not expect that his efforts spanning more than a decade would quickly come under intense fire—but they did. This is not to suggest that Galvani lacked strong supporters, for he did have backers for all or key parts of his thesis. In particular, his nephew Giovanni Aldini (1762–1834), Eusebio Valli (1762–1816), and Johann Friedrich Blumenbach (1752–1840) were among the prominent scientists openly praising what he had done. But he also had his share of adversaries, the most notable by far being Alessandro Volta, a fellow Italian who also differed from him politically. Volta’s inventions and ideas, some stemming from his attempts to refute Galvani’s electrical thesis, would revolutionize physics and help make his name exceedingly well known (and eponymic) around the world. With this in mind, let us now turn to Volta’s criticisms of Galvani’s experiments and conclusions, and examine how they affected what would happen to the animal spirit doctrine.

Galvani’s Electrical Spirit Assailed Alessandro Volta (Fig. 15.3) was born into an aristocratic family in Como, a scenic lake town in northern Italy, in 1745.26 He taught in the public schools and became a professor of physics at the Royal School in Como in 1774. Shortly thereafter, he invented his electrophorus for producing static electricity in a new way. He was also drawn to gasses later in the 1770s, and is considered the discoverer of methane, commonly known as marsh gas, on which he did many

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From Fishes to Frogs and Nerve Electricity experiments. Yet he never abandoned his interest in electricity at this time, studying, among other things, electrical capacitance. Although he lacked a university degree, Volta’s accomplishments were widely recognized and in 1779 he became professor of experimental physics at the University of Pavia, a position he would occupy for almost a quarter of a century.

Volta learned about Galvani’s “great achievement” in 1792, a year after having been elected into the Royal Society of London. The secretary of Bologna’s Istituto had sent a copy of Galvani’s opus to another professor at the University of Pavia, who passed it on to him. With his interest in Figure 15.3: Alessandro Volta (1745– all branches of the sciences and 1827), the Italian physicist who deep interest in “weak” questioned much of what Galvani and his electricity, Volta set forth to try nephew Aldini wrote about frog and to verify his countryman’s mammal electricity. Volta did not, findings with prepared frogs of however, question that some fishes might his own. At the outset, he be electrical. responded favorably to Galvani’s work on animal electricity, calling it a great and stupendous discovery akin to Franklin’s evidence for lightning being electrical.27 But when he started to focus more on the use of metals in these experiments, his thinking changed dramatically—not about all animal electricity, since he continued to accept specialized fish electricity, but about frogs and other animals without discernable electrical organs that also do not deliver shocks.28 The more Volta experimented with metals, the more he began to believe that putting two or more different metals together could produce electricity. Although so weak that the usual physical instruments could not detect it, this metal-generated electricity could act as a stimulus for muscle contractions with prepared frogs.

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From Fishes to Frogs and Nerve Electricity Volta now found that combining metals could produce different taste sensations when put into a circuit with the tongue. Along with experiments involving metals applied to the nerves alone, rather than to a nerve and a muscle, these findings could not be explained with recourse to Galvani’s model. After all, the Bolognese physician had maintained that the nerves are no more than conductors of electricity, which he thought the muscle fibers must store. Hence, Galvani’s broad concept of “animal electricity” increasingly seemed to be based on an experimental artifact, at least in Volta’s mind. As Volta viewed it starting in 1792, Galvani was mistaken when he attributed electricity to frogs (p.240) and other animals without welldefined electrical organs. Rather, the true source of Galvani’s socalled “animal electricity” was, in fact, located outside the animal. Electricity from metals could produce movements or specific sensations, depending on the type of nerve stimulated, Galvani’s ideas about frogs and even our physiology being no more than misguided speculations based on flawed experiments.29

Figure 15.4: A copperplate from Aldini Galvani neither took Volta’s (1804) showing some experiments on criticisms passively nor animal electricity that he performed on defended his own experiments guillotined or otherwise executed dogmatically. Instead, he humans. accepted the possibility that some of his experiments might have been flawed, and he set forth to conduct new experiments involving no metals or just one metal in his circuits to bolster his case for animal electricity. Some of his new experiments were conducted with the help of his nephew Giovanni Aldini, who continued to study animal electricity after his uncle passed away. In addition to his work on frogs and common animals, Aldini went on to conduct some well-publicized experiments on recently executed criminals (Fig. 15.4)30 and, although less well known, with medical electricity for various conditions (Fig. 15.5).31 One of Galvani’s most important new experiments was published in an anonymous tract, Trattato dell’Arco Conduttore, in 1794. It involved directly touching a nerve to an exposed frog’s muscle. Although there were no metals in the circuit, the muscle still contracted.32 This ingenious experiment drew some fence-sitters over to the internal electricity camp, and it led to more thinking about the part or parts of the body actually producing the electricity. Page 10 of 35

From Fishes to Frogs and Nerve Electricity Although Volta argued that even this clever experiment still fell short of being a proof of animal electricity, he now began to ponder the possibility that two heterogeneous physical materials, and not just two metals, might produce findings of this sort. In effect, he now wondered whether a nerve and a muscle, if separated by a moist conductor (e.g., saline, blood), might form a circuit capable of producing weak electricity. A few years later, Galvani placed the two legs of a prepared frog apart and used the sciatic nerve from one of the legs to form a small arc to the nerve innervating the (p.241) other leg.33 To his delight, he was able to obtain muscle contractions, and this time no heterogeneous materials were even present.

Volta, who had just succeeded in actually measuring weak

Figure 15.5: Some of Aldini’s (1803) electrical experiments on patients we

metallic electricity with a newly would today classify as depressive and, at devised physical instrument, least in one case, most likely was nevertheless still not ready schizophrenic. to conclude that there is both metallic electricity and frog electricity. Although his mind was now more focused on devising ways to multiply weak metallic electricity, he continued to challenge Galvani’s conclusions. In particular, he pointed to the physical effects of placing one nerve on top of another, and to possible impurities in the fluids bathing the preparations. These were real possibilities, even if only remote, and they seemed virtually impossible to disentangle in the experiments being conducted at this “charged” moment in time. While Volta was busy with his own experimenting, Galvani headed to the nearby Adriatic Sea to conduct some studies on the local torpedoes. His dissections and physiological experiments—some involving cutting nerves and ablating brain substance—were largely replications of what others had done.34 Still, he returned home feeling even more strongly that electric fish and frog electricity are one and the same. In accord with the law of parsimony, nature would not have invented two different fluids to serve the same purpose. This natural electricity, he continued to maintain, is similar to the electricity he could generate artificially or capture from the sky. Interestingly, Galvani’s fish studies seemed to direct Volta’s attention back to electric fishes. This led him to his revolutionary organe électrique artificiel or pile, which was modeled on the torpedo’s electric organs. Volta introduced his new type of battery, which could emit streams of electricity and recharge itself, in a letter published in the Page 11 of 35

From Fishes to Frogs and Nerve Electricity Philosophical Transactions of the Royal Society of London in 1800.35 His letter was written in French and included a picture (Fig. 15.6).

Volta’s battery multiplied the weak electricity from many individual bimetallic disks to produce perceptible effects. And, as might be expected, this had many ramifications. For some, how it multiplied the effects of otherwise subtle electricity and how its discharge felt to a subject in an experiment made it seem even more likely that fish electricity is no different from “genuine” electricity. Baron Alexander von Humboldt (1769–1859), who had initially conceived of a family of electricities based on differences he had obtained in some of his own experiments, was one such person. 242)

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36

(p.

Figure 15.6: Volta’s pile as shown in the Philosophical Transactions of the Royal Society of London in 1800.

From Fishes to Frogs and Nerve Electricity But although Humboldt (Fig. 15.7)37 was now more willing to accept the notion of a universal electrical force, the matter of frog electricity, and really electricity in more than a few strongly electric fishes, still had its critics demanding more telling research.

Indeed, some scientists scoffed at the very idea that Volta’s different metals, and by extension his battery, produced electricity that is identical to artificial electricity. This was largely because his metals could not produce sparks or sounds, or make pith balls move, even when arranged into piles. Volta’s explanations in terms of differences in tension and other Figure 15.7: Alexander von Humboldt factors were not understood or (1769–1859), the famous German accepted by everyone. The explorer and natural philosopher. continued use of the term Humboldt studied animal electricity in “galvanism” for the metallic Europe before conducting experiments in force (which had irked Volta 1800 on electric eels in what is now from the start, because the Venezuela. He is 26 years old in this discovery with metals was his, depiction. and not Galvani’s) and for the fish force, at least in some circles, continued to suggest fundamental (qualitative) differences among the forces from different sources. What remained to be properly recognized at this time was the fact that the physiological findings in many of these experiments involved two sources of electricity: one was from an external source and the other was generated internally.38 Another century and a half would have to pass before innovative scientists would achieve a full understanding of how externally applied electricity could activate the electricity intrinsic to a nerve or muscle.

The Changing Zeitgeist

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From Fishes to Frogs and Nerve Electricity Volta’s prestige, especially after his invention of the battery, was enormous, and he received many honors, awards, and prizes for his contributions to the field of electricity. But while his work stimulated an enormous amount of new research into the physics of electricity in the opening decades of the 19th century, his strong stance against Galvani and his theory that there is intrinsic electricity in frogs and other animals appears to have inhibited new research on physiological electricity at this time. In a mid-century historical review we read that, after the voltaic pile or battery was invented, Volta’s opinions gained a complete victory. Aldini alone exerted himself for the lost cause of animal electricity.…Animal electricity disappeared with Aldini’s work [his book of 1804] for a space of twenty-three years; until 1827, when Nobili demonstrated the electro-magnetic action of the current of the frog. Meanwhile, there appeared only a few scattered facts in support of the fundamental experiment of muscular contraction excited without the intervention of any metal.39 Thus, there was a relative lull in new research on animal electricity that lasted until Volta’s death in 1827, even though there had been some major advances in physiology. One of the most significant was the discovery that the dorsal roots of the spinal cord are sensory and that the ventral roots are motor.40 This idea was promoted by Charles Bell (1774–1882), a Scot then working in London, and François Magendie (1783–1855), who was in Paris.41 Yet both Bell and Magendie tended to shy away from speculating about the agent within the nerves. For example, at the end of an 1826 article on how there are both nerves from the brain to the muscles and from the muscles to the brain, Bell warns that “It is natural to suppose that the galvanic influence might be brought to bear on this subject; but I may be permitted to suggest to any one who pursues it in this way, that it will be necessary to distinguish the effects produced by the nerve as a mere conductor, and when performing its living functions.”42 In his 1811 Idea of a New Anatomy of the Brain, he did not even go this far, saying nothing at all about the agent underlying nerve and (p.243) muscle physiology.43 As for Magendie, he maintained that he would not delve into unknown or metaphysical constructs (e.g., the force vitale), or deal with physiological speculations that could not be perceived by the senses and substantiated. Words to this effect can be found in his Précis Élémentaire de Physiologie (An Elementary Treatise on Human Physiology).44 But as mentioned, research on nerve and muscle electricity started to pick up again late in the 1820s. And during the 1830s in particular, many new and revealing findings were coming forth from Italy, both from Italians and from visitors hailing from other parts of Europe. Page 14 of 35

From Fishes to Frogs and Nerve Electricity Several notable changes characterized how the newer research was conducted. Needless to say, there were new tools, new strategies, and new demands, just as was true in previous eras. But as the 19th century progressed, technologically skilled and well-read professionals affiliated with universities and other institutes played ever-greater roles in advancing the sciences. And with these and other changes, different ways of thinking about the nerve and muscle force, and different ways to frame new findings into a larger picture, were presented. One thing that stands out as especially notable to us, given the theme of this book, is how the term “animal spirit(s),” which had been so popular through the 18th century, seems to have virtually disappeared from the mainstream scientific literature early in the 19th century. But more than just this glaring omission, some other fundamental tenets of the animal spirit doctrine were also being shunned or criticized prior to mid-century. One was the idea that a fluid made in the cerebrum flows through the nerves to be stored in the muscles. As for what the once-speculative fluid might be, opposition to the idea that frog and even our physiology might be electrical diminished significantly during the post-Volta era, this being a consequence of new, more informative experiments. Instead, 19th-century scientists now gravitated to the idea that the muscles and nerves must somehow generate the intrinsic electricity, as opposed to it being made by friction or another process within the cerebrum for transport through passive nerve conduits to the muscles. What would take considerably more time, of course, would be a good understanding of how such things could actually happen. But even before mid-century, some researchers were thinking about chemistry, and specifically about charged molecules.

New Findings from Italy Early on, the subjects in the physiological experiments continued to be electric fishes and frogs, increasingly seen as having more in common than meets the eye. The electric fish experiments that were conducted in the first half of the 19th century were important because they provided even more evidence for the reality of animal electricity and its various features. In this domain, John Davy (1790–1868), the younger brother of famed British chemist and inventor Humphry Davy (1778–1829), who also studied electric fishes,45 merits attention.

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From Fishes to Frogs and Nerve Electricity Trained in medicine at Edinburgh, John Davy was a chemist, a naval surgeon, and inspector of hospitals for the British Army. As such, he was an extremely well-traveled man, going to India, the West Indies, and around the Mediterranean region. Familiar with torpedoes, and having personally experimented with them, early in the 1830s he reported that their discharges have even more in common with electrical machines than had been thought.46 Among other things, he showed that they could produce various chemical transformations, heat wires, and even magnetize a needle. Moreover, he was able to detect a torpedo’s shock with a physical instrument, as opposed to watching a frog jump or a muscle preparation twitch, or personally experiencing the discharge. Other torpedo experimenters congregating in Italy, including Gilbert Breschet (1784–1845), Antoine Caesar Becquerel (1788–1878), Carlo Matteucci (1811– 1868), Leopoldo Nobili (1784–1835), and Santi Linari (1777–1858), were also able to show some of these effects, and they established the correct polarity of the torpedo’s discharge (the back of the torpedo is positive and the belly is negative). Sparks were even obtained from torpedoes at this time (e.g., by Linari and Matteucci)—this indicator of electricity having only been observed with electric eels prior to the 1830s. Electrostatic and repulsive effects, also long considered key features of charged bodies, also were witnessed.47 In his 1834 publication, John Davy wrote: “I have not witnessed in the Torpedos of the Mediterranean; nor, indeed, have I been able to associate any visible sign, any apparent movement of the fish, with the electrical discharge.”48 The realization that torpedo muscles do not have to move while shocks are released added the last nail to the coffin of the mechanical theories proposed by Redi and Lorenzini, which were then endorsed by Réaumur and others (see Chapter 13). In contrast, this finding was very much in accord with what one would expect if these fishes actually produce their effects electrically. Thus, pretty much all of the earlier demands for showing that torpedoes are electrical had been achieved prior to mid-century. Nevertheless, the source of the electricity remained far from understood. In 1836, Becquerel was still thinking that the electricity responsible for the shocks is developed in the (p.244) brain and then conveyed to the electric organs, where it charged the little cylinders making up those organs. As we have seen, change “electric organs” to “muscles” and this schema should be more than reminiscent of the structure common to the older animal spirit doctrine. Matteucci was also of this opinion at first, but by 1844 he found it untenable, based on new research he had conducted.

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From Fishes to Frogs and Nerve Electricity These early-19th-century researchers tended to think broadly, guided by the belief that their new findings with torpedoes would also shed light on nerve and muscle functions in other animals. Hence, they also engaged in studies on other animals, usually frogs, in their broad endeavors. Leopoldo Nobili and Carlo Matteucci did this, and they not only succeeded in measuring frog-generated electricity, but they also started to draw attention away from earlier ideas to the possibility that the electricity might be made in the muscles and nerves themselves. Nobili, who was Professor of Physics at the Museum of Physics and Natural History of Florence, did this in 1827 using his new “astatic” galvanometer. He connected the poles of his instrument to two fluid-filled glass containers, one containing a frog’s legs and the other a spinal cord. He called the electricity that he recorded the “frog current” or “proper current.”49 But he did not attribute the weak electricity to physiological events. Instead, he reasoned that a smaller mass of nerves must cool more intensely and rapidly than a larger mass of muscles, and that the temperature differences caused by evaporation could generate thermoelectric currents. Matteucci, who had been stimulated by Galvani’s ideas and had been experimenting with bioelectricity since 1830, repeated and modified Nobili’s experiments while in Ravenna, the town in which he served as the head of a hospital and professor of physics. In 1844, he pointed to the muscles as the main source of the current.50 He found that the current would appear only when one of his electrodes was placed on the intact surface of the muscle and the other was placed on the cut or otherwise injured surface. He also established the polarity of the current, writing that the injured part is normally negative relative to the intact surface. Matteucci even constructed a frog “pile” using half-thighs. With each new halfthigh that he added to the pile, the galvanometer needle moved even more. It did not matter whether he used frogs, local (non-electric) eels, or other animal parts in his experiments, provided direct contacts were made between the severed and intact surfaces of the muscles. Matteucci’s stacked muscle preparations did more than just look like the components in Volta’s battery or those of a fish electric organ; they also functioned in comparable ways, producing heat, electrochemical decomposition, and other effects associated with electricity.

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From Fishes to Frogs and Nerve Electricity What Matteucci was able to accomplish helped to show that muscle electricity is a biological phenomenon basic to life: not a thermal, chemical, or physical process of interest to chemists but of little importance for the living organism. But at the same time, he was unable to come forth with enough evidence for nerve electricity to extend his thinking about the muscles to nerve physiology, or to present a more complete model of neuromuscular physiology, including just how the will or brain might control the voluntary muscles. Still, the term “animal spirit(s)” is notably absent from his basic research papers, as he attempted to distance himself from older terms and concepts that could not be supported experimentally, much as had been true for Bell and Magendie. Matteucci was a pioneer who broke new ground, and we can only guess what he might have concluded had he opted to continue his physiological experiments. But he now entered national politics, leaving the door open for some German researchers to step forth and shed further light on the nature of nerve and muscle physiology.

German Physiological Advances Emil du Bois-Reymond (1818–1896) studied physiology in Berlin under Johannes Peter Müller (1801–1858), who, perhaps sensing an opening, introduced him to Matteucci’s writings on nerves and muscles while he was an aspiring student. Born in Koblenz in 1801, Johannes Müller had gone to Bonn University in 1819, where he studied medicine and then rose through the ranks to become extraordinary professor (in 1826) and then ordinary professor of physiology (in 1830).51 Three years later, he accepted the chair of anatomy and physiology at the University of Berlin, a post he would hold until his death in 1858. Not one for mutilating animals (he strongly opposed vivisection), Müller approached physiology largely through comparative anatomy and in other, less invasive ways. Müller’s “Law of Specific Nerve Energies,” which holds that nerves produce the sensations unique to them no matter how stimulated, had a dramatic impact on physiology. Additionally, his two-volume Handbuch der Physiologie des Menschen, which came out in 1833 and 1840 (and was translated into other languages), became the standard in the field, displacing Haller’s monumental Elementa physiologiae (1757–66) from its post. Müller’s fame also had much to do with his students and disciples, many wanting to give physiology a firmer basis in physics and chemistry. These students called for a new physiology without recourse to Lebenskraft, a term that pertained to an ill-defined, governing life force, and a vitalistic conception that permeated Müller’s “older” way of thinking. They saw vitalism as muddying the waters of good science, and they maintained that all physiological processes should be explainable by physics and chemistry, without recourse to metaphysical forces of any sort.52 Page 18 of 35

From Fishes to Frogs and Nerve Electricity (p.245) Emil du Bois-Reymond was a leader in this materialistic and reductionistic movement. He was born in Berlin in 1818 and studied physiology and medicine under Müller in this Prussian city.53 He was skilled with instruments, had a fertile mind, and had already become a dominant force in nerve and muscle physiology before Müller died in 1858, at which time he acquired his mentor’s coveted chair at the University of Berlin. Over his lengthy career, he would publish an extraordinary number of experiments and some very important physiology books.54 Being brash, arrogant, and conceited, however, he also engaged in polemics and made many enemies. Du Bois-Reymond, like the Italians, operated on the assumption that studies on electric fishes would allow him to understand other animals better, and vice versa. He also believed that muscle research would improve an understanding of the nerves, and that understanding the nerves would help him understand the muscles. He expressed these guiding research thoughts very succinctly when he wrote that an understanding of “nerves, muscles and electric organs [in fishes] is not divisible but has to be regarded as a whole.”55 Hence, he studied muscles, nerves, and fish electric organs, even building a heated aquarium in Berlin to house imported electric fishes, which required warmer water than ordinarily could be provided. Because du Bois-Reymond opposed all terms and concepts that smacked of metaphysics and were not firmly based in physics and chemistry, it is hardly surprising that he does not write about an animal spirit, other than in its historical context. Quite literally, the term is too “spiritual,” occult, and unscientific for him, it being the sort of thing that has to be discarded for real science to advance. Instead, his intention is to focus on electricity as a natural biological force. His goal will be to try to show its reality across the animal kingdom, to record it from nerves and muscles, to understand its natural laws, and to account for it with findings from chemistry. Stimulated by what Matteucci had written, but depicting him as a rival who made many regrettable mistakes, du Bois-Reymond was able to go beyond Matteucci by demonstrating that there are electrical currents in the nerves, as well as the muscles. He began this research in 1841, and it served as the basis for his 1843 doctoral thesis and the thinking in his Untersuchungen über thierische Elektricität, his two large volumes on animal electricity.56 We now know that some of his early findings were due to artifacts. Nevertheless, his early investigations with frogs, particularly of the sciatic nerve and of the gastrocnemius and sartorius muscles, greatly affected thinking at the time. Using a sensitive galvanometer of his own design, he described a nerve current and a muscle current, and he maintained that these currents can be detected in intact preparations and are “fundamental phenomena” of animal physiology.

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From Fishes to Frogs and Nerve Electricity Du Bois-Reymond’s various experiments indicated that the surface of the fiber is positive and that the transverse or center section is negative, at least when it is in a resting state. He writes that this polarized condition could be disrupted, however, by an appropriate natural stimulus or by cutting or injuring the fiber. When this happens, the Ruhestrom, or resting current, diminishes in intensity and there is a propagated wave of excitation. He referred to the decrease in the intensity of current as the negative Schwankung, meaning “negative variation” or “negative oscillation.” Today physiologists call this sharp drop and even transient reversal in polarization an “action potential.”57 Du Bois-Reymond had little use for the old Leyden jar theory of nerve and muscle physiology. In the historical introduction to his 1848 treatise on electricity, he explained that Galvani should have paid more attention to experiments in which he obtained contractions just by touching a nerve to a muscle.58 Nevertheless, he praised Galvani for his discovery of animal electricity (“Galvani really discovered…the electricity inherent in the nerves and muscles”),59 even presenting himself as a follower of Galvani and Humboldt (who, we might note, was highly instrumental in advancing his career).60 But unlike these scientists, he now proceeded to formulate a molecular theory to account for his observations, specifically the resting current and the negative variation. At this juncture, we should mention that other physiologists were also starting to think that nerve electricity, although still referred to as galvanism in some writings, must have something to do with molecules, about which they could only theorize. For example, in the 1837 (edited) edition of John Fletcher’s (1792– 1836) Rudiments of Physiology, there is a discussion of the nerves, how their powers can be activated, and how such things as passions and instincts are conveyed. We read that “we are almost entirely in the dark” about nerve function, but that the nerves have a power that is always at hand. Later in the same paragraph, we are told that in order to develop this power, the nerves in which it is resident must undergo some molecular change, as a consequence of the primary irritation which they are to extend to distal parts, similar to that which they undergo from a direct chemical or mechanical stimulus…Of the nature of this molecular change however we are utterly ignorant: it is in all probability sui generis [of its own kind], and such as cannot be illustrated by a reference to any thing out of the body—we recognize this change only by the powers which it develops, and we recognize those powers only by their effects.61

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From Fishes to Frogs and Nerve Electricity Du Bois-Reymond was much less inhibited when it came to writing about hypothesized molecules and how he felt they must be arranged. Based on his conclusions about fibers and bioelectrical currents, he wrote about “electromotive molecules.” He described these molecules as “peripolar,” the critical feature being that “they must have two negative (p.246) polar zones, and a positive equatorial zone.”62 When lined up properly, as shown in Figure 15.8, they would model a fiber in the resting state: “the vertical boundary represents the longitudinal, the horizontal boundary the transverse section, the shaded background is the wet conductor.”63 He maintained that a stimulus disrupting this orderly polarized arrangement would produce the negative Schwankung or negative variation. Notably, the negative variation was no more than the disappearance of the current existing in the resting condition in his theoretical schema. In part because du BoisReymond did not appreciate the role of the cell membrane in maintaining the resting current or in generating the negative variation, his theory would be found to be flawed.

Figure 15.8: Emil du Bois-Reymond’s envisioned molecules, showing how they might be charged.

Hermann Helmholtz (1821– 1894), another Müller student who championed a physicalchemical orientation to the sciences, should be recognized at this juncture. Although Johannes Müller had doubted whether scientists could ever measure the speed of nerve conduction,64 Helmholtz (Fig. 15.9) was able to do this in a series of experiments that he had started in 1849.65 His research involved both frogs and humans, and it included both sensory and motor nerves. Du BoisReymond helped him with some of his methodologies, suggesting that he should have his galvanometer turn

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From Fishes to Frogs and Nerve Electricity on with the initiation of the electrical stimulus to a nerve, and shut off when the muscle begins its contraction, which is what Helmholtz did in some of his studies.

Helmholtz’s experiments revealed a speed of nerve conduction of about 30 meters per second, shattering vitalistic and metaphysical beliefs about the nerve force being so fast that it could never be measured. Nevertheless, the nerves did not behave like metal cables, to which they had often been compared. The nerves not only conducted more slowly as the temperature Figure 15.9: Hermann Helmholtz (1821– dropped, but the muscle 1894), the first scientist to correctly twitches following nerve estimate the speed of nerve conduction in stimulation were much slower frogs and humans based on experiments. than would be expected with electricity shooting down an intact cable. Such observations were not lost on du Bois-Reymond. They further suggested chemical reactions, bolstering the case for the kind of molecular chemistry he was championing. It should be noted that Santiago Ramón y Cajal’s (1852–1934) neuron theory and Sir Charles Sherrington’s (1857–1952) concept of synapse were still decades away. Ludimar Hermann (1838–1914), yet another physiologist who had studied under Müller, would become one of the most vocal and aggressive critics of du BoisReymond’s model, even though he had also studied physiology with him. The vitriolic squabbling had much to do with Hermann being unable to record the resting current in intact fibers, a finding central to du Bois-Reymond’s theorizing. This being the case, Hermann hypothesized that the Actionsstrom (“action current”) always stems from injuries. An appropriate stimulus, he maintained, would actually produce something like an injury, triggering local chemical processes and electricity, which would flow from the excited part of the (p.247) fiber to nearby zones. Hermann’s theoretical conception would be called Kernleitertheorie or “core conductor theory”; although not perfect, it proved to be an important step in the right direction.

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From Fishes to Frogs and Nerve Electricity Although Hermann’s thinking led du Bois-Reymond to modify his electric molecules theory, the reality of the cell membrane, which was still in dispute, continued to elude both investigators. Julius Bernstein (1839–1917), in contrast, would now bring it to the fore.66 Bernstein was not a Johannes Müller student, but he did study under du Bois-Reymond and Helmholtz after leaving Breslau in 1860 for further training at the University of Berlin, and he served as Helmholtz’s assistant at Heidelberg. After leaving Heidelberg, he worked in Halle from 1873 to 1911. Bernstein measured the speed of du Bois-Reymond’s negative variation with a sensitive rheotome (“current slicer”) before even leaving Heidelberg, obtaining values that confirmed Helmholtz’s earlier estimates for the speed of nerve conduction, in effect showing that they are one and the same thing. He also managed to measure the time course for the temporary excitation, finding it lasts only about a millisecond. And he even discovered that the negative variation does not always go to 0 during excitation, but can overshoot this value into positive territory. Nevertheless, he would downplay this last finding, which suggested that there might be more than just a neutralization of the resting condition, as had been maintained by his mentor, du Bois-Reymond.67 Bernstein’s electrochemical Membrantheorie was published in 1902, and it was based on what he had learned in his own experiments and new developments in the literature, including research on semi-permeable membranes and ion diffusion. Exceptionally skilled in physics and chemistry, as well as physiology, he discussed how two different electrolytic solutions separated by a semipermeable membrane could generate an electrical potential in a muscle. He also addressed how some charged molecules could move between the intracellular and extracellular fluids, thereby accounting for changes in the electrical potential. Bernstein’s new thinking bridged the divide that had been characterizing the German literature. His reasoning was based on du Bois-Reymond’s premise that there is, in fact, a resting potential that could be associated with nerve fibers. But it also incorporated some of Hermann’s Kernleitertheorie, which described how a stimulus could disrupt the local chemistry, producing an electrical change that would spread spatially and temporally to adjacent parts of the fiber. Nevertheless, Bernstein’s theory fell short of today’s conceptions in two major ways. First, it did not adequately go into the structure of the membrane, although Bernstein could have incorporated what others had recently learned about lipids into his model. And second, although he wrote about an outward flow of potassium (K+) across the membrane, he had surprisingly little to say about an influx of sodium (Na+) from the external fluid at the time of activation.

Into More Modern Times Page 23 of 35

From Fishes to Frogs and Nerve Electricity It is not our purpose to go into 20th-century developments in detail, since numerous players and laboratories were involved, and since many books and articles have been written about how these newer discoveries and insights shaped electrophysiology and neuronal biochemistry. But because this newer work allowed researchers to understand exactly how molecular and membrane events actually provide the foundations for nerve electricity and transmission of the electrical impulse, it is necessary to summarize, even if briefly, some of the milestones that were crossed in more modern times. As we have emphasized, the need to understand perplexing phenomena has repeatedly stimulated efforts to develop better tools, techniques, and preparations, which in turn have allowed researchers to see things more clearly. With regard to nerve electricity, this long-recognized axiom continued to hold during the 20th century, as did the often-overlooked need to keep an open mind. In 1902, the same year in which Bernstein published his electrochemical Membrantheorie, English physiologist Charles Overton (1865–1933) published two important articles.68 They were about lipids being basic to the structure of the muscle membrane and the importance of sodium. Overton correctly contended that bioelectrical phenomena depend on concentrations of potassium and sodium, with potassium having a greater internal concentration and sodium being the prevailing extracellular cation.69 He also recognized that a massive influx of positively charged sodium could change the polarity of the cell, accounting for its temporary overshoot from negative into positive territory. English zoologist John Z. Young (1907–1997) deserves mention because he was the individual who directed scientists to an organism that would allow them to make further strides in understanding the neuronal chemistry and biophysics underlying electrophysiology. Young had been studying squid, and he drew attention to this creature’s giant axon—an axon that is far greater in diameter than those of frogs or even the large farm animals sometimes used for research purposes. Young’s papers came out in 1936, and they enticed some physiologists to find out what they could learn with this saltwater wonder of nature.70 Because of its large diameter, several investigators quickly realized that they could insert a fine wire into it, one that could serve as an electrode for recording purposes. The prevailing feeling at the time was that this sort of thing was impossible to do with the much thinner axons of other animals, although it would be something that might reveal some of physiology’s deepest secrets. This ability to place electrodes intracellularly allowed Alan Hodgkin (1914–1998) and Andrew Huxley (b. 1917), two future Nobel Prize winners from England, and Kenneth Cole (1900–1984) and Howard Curtis (1906–1972), in the United States, to record transmembrane potentials in the resting state and during excitation. This accomplishment (p.248) Page 24 of 35

From Fishes to Frogs and Nerve Electricity was achieved in 1939 and 1940.71 As a result, researchers were able to measure the resting potential (discovered to be about –50 mV) and to see the overshoot following the action potential that Bernstein had noted somewhat in passing, when studying frogs with what had been state-of-the-art tools in 1868 (Fig. 15.10).

As historians of modern electrophysiology know, the squid’s giant axon is also important because it allowed investigators to confirm the role of sodium in neuronal physiology. In 1949, Alan Hodgkin and Bernard Katz

Figure 15.10: Hodgkin and Huxley’s 1939 picture of the squid’s giant axon action potential (top), recorded with an

internal electrode. Ordinate = internal (1911–2003), another future potential in mV; Abscissa = 2 msec. Nobel Prize winner, succeeded (From Nature, 1939, vol. 144, p. 710, in showing that action with permission of the publisher) potentials in the squid’s giant axon decrease in amplitude when extracellular sodium is reduced. They deduced from these and other experiments that a selective increase in membrane permeability to sodium ions is, in fact, responsible for the initiation of the nerve impulse. Such thinking was confirmed using electrical instruments that drew on technologies that engineers had worked out during the Second World War, including better amplifiers and oscilloscopes. For physiologists, one of the newest and most important technological developments was the voltage clamp technique, which came forth in 1949.72 It utilized a fast-feedback electrical circuit that allowed researchers to set an axon’s potential at a chosen value for experimentation. Using this technique on the squid’s giant axon, Hodgkin and Huxley were able to work out the time course of the transmembrane flows of sodium and potassium ions that underlie the action potential.73 Some decades later, in the late 1980s and early 1990s, molecular biologists succeeded in isolating the large membrane-embedded protein molecules responsible for these transmembrane flows. The molecular structure and physiology of these voltage-dependent gates are now reasonably well understood at the atomic level. Thus, by the start of the 21st century, the age-old dream of understanding how nerve fibers transmit information from brain to periphery and vice versa was finally realized.74 Page 25 of 35

From Fishes to Frogs and Nerve Electricity In addition to the voltage clamp with its associated electronics, many other techniques have been developed and used by experimentalists in their endeavors to understand the biology of nerve fibers. Radioactive tracers and fluorescent labeling are among the tools that have now allowed researchers to show that particulate matter really does flow down the axon. This flow, called “axoplasmic transport,” involves the movement of proteins, synaptic vesicles, lipids, and various other biochemicals along the axon. The flow occurs in both directions, both from the nerve cell body or perikaryon towards the synaptic terminal and backwards, from the terminal, towards the perikaryon. It has been shown, moreover, that the “outward” flow, from the perikaryon to the axon terminals, occurs at two rates: fast (c. 50–400 mm/day) and slow (c. 8 mm/ day). “Fast” axoplasmic flow takes place along microtubule “tramlines” that run the length of the axon. The motive force for this flow is provided by mechanoenzymes (e.g., kinesins, dyneins), also called “motor proteins,” which are dependent upon metabolic energy (ATP). This flow carries, among other things, the synaptic vesicles that ultimately release their contents into the synaptic gap. The slow flow contains elements of the cytoskeleton and other materials necessary for axonal maintenance and growth. The “retrograde” flow, back from the terminal to the perikaryon, contains worn membrane parts and other waste material, as well as neurotrophic and other factors taken up at the synapse. The flowing of material down and up axons reminds us of earlier times, when many investigators believed that, in addition to spirituous agents coursing through or along hollow nerve tubes to make muscles contract, there was a flow of a second fluid, one that is more gelatinous. The latter was believed to have nutritive functions and it made its way more slowly down the fiber. Frenchman Jean-Paul Marat (1743–1793) embraced this way of thinking. Marat, the self-styled ami du peuple (“friend of the people”), is far better remembered today for his fanatical politics during the “Terror” than for his scientific ideas. Nevertheless, he published a lengthy “psychophysiological” text in 1773 titled A Philosophical Essay on Man. In his essay, based heavily on first-hand dissections, Marat wrote that the nerves contain a fluid, “composed of a two-fold substance: a spirituous part, called animal spirits and a gelatinous juice distinguished by the name of nervous fluid.”75 Like many others, he firmly believed that the nerves must have a double function: one involved with transmitting (p.249) “animal spirits,” the messengers of the “soul,” and another for delivering a nutritious juice to other body parts.

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From Fishes to Frogs and Nerve Electricity Thus, it is fascinating to think that Marat, like many other natural philosophers and scientists, who had so little to go on, were really not far off the mark about different substances flowing through the nerves. It might be said that the history we have traced has, in fact, been largely one characterized by redefinitions, and that, in at least some instances, today’s neuroscientists have managed to voyage full circle, even if only some might make the connection.

Looking Back In summary, Galvani’s 1791 concept of nerve electricity in more than a few specialized fish, or, put somewhat differently, the idea that the animal spirit is electricity, drew experimental support over the course of the 19th century, but required 20th-century developments for researchers to explain correctly what they and their predecessors had been witnessing. Thus, as important as Galvani has been for our story, the fact of the matter is that his work had both precedents and elements that still had to be studied more intensively, and then appropriately modified, before the nerves and muscles of electric fishes, frogs, squid, humans, and other animals could really be understood as biological generators of electricity. As we have now shown, the immediate precedents for Galvani’s work on frogs can be found in electric fish studies conducted between 1750 and 1776. The challenge facing the fish researchers was to prove that any animal could be electrical, since animals possess moist bodies that would seemingly allow electricity, external or internal, to run amok. Studies on electric fish showed that, even though physiological electricity seemed to defy the laws of physics (as well as plain old-fashioned common sense), some animals do manage to generate and use what appeared to be electricity in adaptive ways—that is, that certain fishes are electrical and survive beautifully in their murky and otherwise challenging environments as a result of being able to discharge bursts of electricity to secure food and ward off predators.76 The evidence for this revelation began with the realization that the electric fish discharges feel like those from properly charged Leyden jars, and that they could be transmitted through conductors, but not non-conductors, of electricity. John Walsh’s ability to demonstrate a spark in darkness with an electric eel in 1776 was the icing on the cake for many 18th-century natural philosophers, although it remained to be determined whether fish electricity really is identical to frictional and atmospheric electricity, and later to the metallic electricity that Volta discovered and studied so creatively and intensively.

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From Fishes to Frogs and Nerve Electricity Galvani was well aware of what had been discovered with electric fishes when conducting his own experiments, which were largely on frogs. He was certainly correct when he suggested that parts of an animal’s electrical machinery might be insulated—there being an oily or fatty layer (now recognized as myelin for the nerves) that might preventing the internally generated electricity from running helter-skelter. His thought that the electricity is probably generated in the brain for transport by the nerves to the muscles would not, however, withstand the test of time. Nor would other thoughts based on how the Leyden jar with its attached wires looks and works. Eighteenth-century researchers were wrong to envision the nerves as passive transmitters of electricity. They failed to realize that both nerves and muscles could manufacture electricity and maintain an electrical charge. Even when attention began to be drawn to this possibility in the 19th century, this possibility was poorly understood and basically left open to speculation. A good understanding of the underlying biochemical and biophysical processes involved would come forth during the middle of the 20th century, although the path to this needed knowledge was paved by late-19th-century and early-20th-century developments. Today, even more is being learned in well-equipped laboratories throughout the world about the features of the molecules and membranes underlying these dynamic events. Thus, what happed to the animal spirit theory was not at all like a massive explosion that in the blink of an eye changed the existing landscape, although several landmark events can be singled out as being especially important: one being Walsh’s successful spark experiment in 1776 and another being Galvani’s treatise of 1791. Rather, what transpired was something considerably slower. It involved a new idea that had features that allowed it to explain things far better than earlier theories, which increasingly had been found wanting and were now seen as flawed. Nevertheless, this newer idea also needed more experimental support for general acceptance, and then newer tools and laboratory preparations to be fully understood.

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From Fishes to Frogs and Nerve Electricity This is essentially how the non-electrical animal spirit doctrine, after various transformations, lost its once-shiny luster. It is also why what Galvani was proclaiming about animal electricity, the brain, the nerves, and the muscles, could not be presented as the final act in this rather long saga. Hence, from multiple perspectives it does not make sense to try to give a firm death date to non-electrical ideas about the nerves and muscles. The same could even be said for the basic structure of the animal spirit doctrine, which took time to be displaced by new ideas about the nerve and muscle electricity that could be supported experimentally. The research path that led to modern electrophysiology, in which different aspects of the animal spirit doctrine were revised, reconstituted, and transformed, could best be described as a meandering road, and what took place along this road was not a quick and simple break with the past. Notes:

(1) Hunter, 1773, 1775. (2) Gardini 1780; Bertholon, 1780, 1786. (3) Volta, 1918, pp. 14–25. This example and others, which Volta included in a letter to Mme. Lenoir de Nanteuil, are discussed in Finger and Piccolino, 2011, pp. 307–308, ff. (4) Galvani, 1791. (5) For a look at Galvani as a skilled and determined scientist with a strong background in medicine, see Bresadola, 1997, 1998, Piccolino and Bresadola, 2003, and Finger and Piccolino, 2011, pp. 307–325. (6) English translators, including I. Bernard Cohen, have called Galvani’s treatise, “Commentary on the Effects of Electricity on Muscular Motion” (see Galvani, 1953). This wording is misleading, as Galvani’s intention was to show more than that electricity can act as an external stimulus for muscle actions. His objective was to show that the nerves and muscles function by internal electricity. (7) Marco Bresadola and Marco Piccolino, two historians who have studied Galvani’s notes in detail, have emphasized this often-overlooked fact in their various scholarly writings. Finger and Piccolino, 2011, pp. 307–325, cited some of this literature and also provided examples to make this clear in their chapter on Galvani. The present authors are deeply indebted to these scholars for their observations and insights, about both Galvani and Volta. (8) Finger and Piccolino, 2011, p. 308. (9) For example, Roche, 1778. Page 29 of 35

From Fishes to Frogs and Nerve Electricity (10) Bresadola, 1997, 1998. (11) Caldani, 1757; Fontana, 1757; Laghi, 1757a,b; also see Chapter 12. (12) Haller’s ideas were discussed in Chapter 12, and this criticism of animal electricity was also brought up in the previous chapter. See Haller, 1767/1786 (1966, trans., p. 221). (13) Galvani, 1937, p. 254. (14) Trans. from Galvani, 1791, p. 399. (15) Trans. from Galvani, 1791, p. 378. (16) Tourmaline has transparent reddish and opaque colorless stripes, and produces electricity when heated, even when broken into smaller fragments. Striated muscle fibers, Galvani postulated, seem to have the same properties as this unusual mineral, whether separated or combined into a composite muscle. (17) Walsh, 1773. (18) Cavendish, 1776. (19) Galvani, 1791; 1953 Cohen translation, p. 73. (20) Ibid., pp. 83–87. (21) Ibid., p. 84. (22) Ibid., p. 78. (23) Translated from Galvani, 1791, p. 402, by Marco Piccolino. Also see ibid., p. 79. (24) Lucia Galeazzi (1743–1790). (25) Trans. from Galvani, 1791, p. 402. (26) For biographical material, see Polvani, 1942, and Pancaldi, 2003. (27) Volta’s various papers from this time period can be found in the first volume of his Le Opere di Alessandro Volta, published in 1918.

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From Fishes to Frogs and Nerve Electricity (28) This story has been told many times in varying degrees of depth and with some differences. Some secondary sources are Polvani, 1942, Pera, 1986, Piccolino and Bresadola, 2003, Bresadola, 2008a,b, and Finger and Piccolino, 2011. Although it is sometimes written that Volta rejected the concept of animal electricity, a closer look at what he wrote about electric fishes and the path that led him to his battery show very clearly that he distinguished between electric fishes and other animals. He did not doubt what physicists and physiologists were claiming about torpedoes, certain catfishes, and the electric eel when it came to electricity, carefully directing his objections to Galvani’s thesis that other animals, such as frogs, must also be electrical. (29) Volta was one of the first scientists to anticipate the law of specific nerve energies, a concept more closely associated with German physiologist Johannes Müller today. See Müller, 1826, 1843; Piccolino and Bresadola, 2003; Finger and Wade, 2002. (30) Aldini’s experiments on recently executed criminals were covered in newspapers and in his own books, including in his text of 1804. To some readers, these experiments were macabre and beyond acceptable, although others recognized their scientific importance. The jump from “galvanic” or electrical experiments to Mary Shelley’s Frankenstein, first published in 1818 and laced with the science of the day, was not as big as it may seem on first glance. (31) Aldini even applied shocks directly to the head for what we would now identify as severe depression and other disabling mental disorders. This idea seems to have originated with Jan Ingenhousz and Benjamin Franklin in the 1780s, and Aldini was among the first investigators to find that cranial shocks really did help. For more on this subject, see Finger, 2006a, pp. 102–115, and Beaudreau and Finger, 2006. (32) Galvani, 1794. (33) Galvani, 1797, p. 16. (34) Galvani, 1797. (35) Volta, 1800.

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From Fishes to Frogs and Nerve Electricity (36) Humboldt studied electricity in his native Germany and elsewhere in Europe for a number of years before going off to South America, where he finally was able to obtain some electric fishes. They included an enfeebled torpedo that was unsuitable for physiological experimentation and, more importantly, some healthy electric eels. He initially thought there might be a family of electricities or at least closely related fluids, because the “galvanic” force he had been investigating with frogs and other animals did not pass through certain substances, such as a piece of charcoal, unlike the electrical discharge from a Leyden jar. But especially after spending time with Volta and seeing his battery in 1805, he changed his mind. In the eel part of the narrative of his journey to the New World, Humboldt praised Volta for his brilliance and achievements, no longer writing about animal galvanism and the metallic force being distinct from genuine electricity. Rather, these forces were now just electricity, albeit from different sources. Finger and Piccolino, 2011, pp. 339–341, discuss Humboldt’s position and how it was changed by what Volta was able to show with his battery. (37) Humboldt, 1797; Humboldt and Bonpland, 1811, 1952/1971, vol. 2, pp. 111– 131. (38) Finger and Piccolino, 2011, pp. 339–350. (39) Du Bois-Reymond and Jones, 1852, pp. 18–19. (40) For original documents related to this discovery, see Cranefield, 1974. (41) See Cranefield, 1974. (42) Bell, 1826, p. 173. (43) Bell, 1811; also in Cranefield, op cit., pp. 3–36. (44) Magendie’s two-volume text first appeared in 1816–17, but it underwent many editions. The fifth edition of 1838 was translated into English by John Revere and published in 1844. In his Introduction, Magendie has a section dealing with “Vital Properties,” and here he tells his readers that we should content ourselves with facts that can be experienced through the senses, not speculations. (45) Humphry Davy experimented with torpedoes in 1814 and again in 1827, while in Italy. As noted by Finger and Piccolino (2011, pp. 353–356), he, unlike his brother John, who he asked to continue his work, did not find the positive electrical effects he was looking for in these rays (e.g., he could not draw a spark from a torpedo).

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From Fishes to Frogs and Nerve Electricity (46) John Davy, 1832, 1834. Davy, who became a member of the Royal Society in 1834, was an extremely talented scientist, although he did not become as internationally famous as his brother. In addition to doing his own experiments, he edited and published nine volumes of his brother’s papers between 1836 and 1840. (47) For details and references related to these researchers’ findings, as well as Michael Faraday’s (1791–1867) contributions (Faraday, 1838, 1839a,b, 1993), see Finger and Piccolino, 2011, pp. 351–374. (48) Davy, 1834, p. 548. (49) Nobili, 1828, 1830. For his new galvanometer, see Nobili, 1825. (50) Matteucci, 1844. (51) Müller’s father was a shoemaker and Johannes initially trained for the Roman Catholic priesthood. He turned to the sciences and medicine at age 18, studying first at Bonn and then in Berlin. Extraordinary professors were subordinate to ordinary professors, who possessed chairs, in the German system. For those with ambition and dedication, the former appointment, sometimes without salary, was looked upon as an important step towards an ordinary professorship. (52) To his credit, Müller continued to support students who opposed his religious and vitalistic views. He encouraged them to pursue their experiments and published some of their findings in the journal he edited, even when their findings seemed to undermine his own way of thinking. For more on Müller’s vitalism and his students, see Otis, 2007. (53) For biographical material, see Estelle du Bois-Reymond, 1927, Rothschuh, 1964, and Finkelstein, 2000, 2003. The authors would like to thank Gabriel Finkelstein for his insights about du Bois-Reymond’s rejection of animal spirits and, along with this venerable concept, Galvani’s Leyden jar model. (54) Most notably, du Bois-Reymond, 1848–84. (55) Dierig, 2000, p. 6. (56) Du Bois-Reymond, 1843, 1848–84. (57) A picture of the action potential appears later in this chapter as Figure 15.10. (58) Du Bois-Reymond, 1848, p. 50. (59) Du Bois-Reymond and Jones, 1852, p. 3.

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From Fishes to Frogs and Nerve Electricity (60) See Otis, 2007, pp. 81, 91, 96, 120–121. (61) Fletcher, 1837, Part IIb, p. 67. (62) Du Bois-Reymond and Jones, 1852, p. 109. (63) Ibid., p. 110. (64) Müller, 1840, p. 729. (65) Helmholtz, 1850a,b; Olesko and Holmes, 1993. (66) Bernstein, 1902, 1912. Also see Lenoir, 1986, and De Palma and Pareti, 2011. (67) Bernstein published these findings in a journal article from 1868 and in a book that came out in 1871. (68) Overton, 1902a,b. (69) Ibid., 1902b, p. 383. (70) Young, 1936a-c. (71) The two milestone papers are Hodgkin and Huxley, 1939, and Cole and Curtis, 1940. (72) Cole, 1949, and Marmont, 1949. (73) Hodgkin and Huxley, 1952a-d. (74) Although reminiscent of du Bois-Reymond’s theoretical forays into molecular chemistry, these molecules differ from those in his model in significant ways, including in alignment and how they function. Du Bois-Reymond arranged his hypothetical molecules lengthwise down a fiber, and he thought that electricity could be transmitted from one molecule to the next by contact. This is quite different from voltage-dependent ion-channel proteins, which are embedded transversely in fiber membranes. Electricity is transmitted from one to the next by local circuits through ionic solutions. Accounts of the biophysics of the nerve impulse can be found in most textbooks of neurophysiology and neuroscience. (75) Marat, 1773, p. 68.

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From Fishes to Frogs and Nerve Electricity (76) Although the nerve electricity story is one involving several strongly electric fishes, we now know that there are even more species of weakly electric fishes. These fishes use their weak electrical pulses for navigation, communication, schooling, mating, and the like, even though the electricity they generate is too weak to stun predators or even to be detected by humans without the help of sophisticated instruments. Attention began to be drawn to these fishes in the 1950s, and within a short period of time they were being intensively studied in laboratories around the world. Today, scientists are publishing more research findings on weakly electric fishes than on the far more powerful electric fishes we have focused on in this section of our book.

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Epilogue

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

Epilogue C. U. M. Smith Eugenio Frixione Stanley Finger William Clower

DOI:10.1093/acprof:oso/9780199766499.003.0016

Abstract and Keywords This chapter summarizes important points that have been made in this book on the emergence of the animal spirit paradigm, its development, and how it was replaced by the notion of electricity. It reviews the ideas and concepts that led to the evolution of the animal spirit doctrine, and then discusses some notable individuals whose works helped improve current knowledge. This chapter also states that the present study tried to provide examples of how new ideas could emerge and how changes can occur in the life sciences. Keywords:   animal spirit paradigm, electricity, life sciences, evolution

It would be a great blessing to Mankind if this most delicate Part [the brain]…were as well understood as the generality of Anatomists and Philosophers imagine it to be. Niels Stensen [Steno], 1669 1 Paradigms gain their status because they are more successful than their competitors in solving a few problems that the group of practitioners has come to recognize as acute. Thomas Kuhn, 1962 2

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Epilogue Just as a prologue is the place for beginnings, so an epilogue is a place for endings—a place for summing up, for looking back, for contemplating. We started in the mists of prehistory with the Homeric bards of the Aegean Bronze Age, and we finished in the rapidly changing biochemical culture that continues to characterize science today. The story we have told has been immense and intricate, a true “adventure of ideas,” to borrow from the title of philosopher Alfred North Whitehead’s (1861–1947) famous book.3 We have seen how the animal spirit idea formed the core of late classical and medieval medical theory, how it slowly began to be dislodged during the Early Modern period, and how it was transformed and eventually replaced by electrical notions. The concept of animal spirit, or pneuma psychikon, meshed well with, and was indeed part of, the worldview in ancient and medieval times. We pointed out how it was elaborated in the intricate ventricular “neurophysiologies” and “neuropsychologies” of the Middle Ages, which were heavily based on far older ideas. The concept persisted virtually intact and unaltered for nearly one-and-ahalf millennia, from Erasistratus, working in Alexandria’s museum at the beginning of the third century BCE, into the European Renaissance. Ultimately, some late Renaissance thinkers began to question it, and the whole interlocking medieval worldview started to show signs of disintegrating during the 16th century—and with it, the unquestioning belief in facets of the animal spirit doctrine that had been so successfully handed down through the ages. A replacement for this older worldview emerged with the epochal works of Copernicus, Galileo, and other thinkers, at a time when many natural philosophers were beginning to value detailed observations and replicable experiments more highly than church dogma or the theories of the great scientific authorities of the past. Historian of science Thomas Kuhn (1922–1996), in his often-cited book The Structure of Scientific Revolutions, wrote about momentous intellectual upheavals resulting in new ways of thinking, especially in the physical sciences, and he popularized the term “paradigm shift” to describe the advent of a new way of thinking about things.4

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Epilogue During the mid-16th century, Nicolaus Copernicus demonstrated that heliocentricity “saved the phenomena” with far less fuss than the palimpsest of epicycles envisaged by traditional thinking, which had placed the earth at the center of the universe. And with his new astronomy, perceptions of the earth and the universe itself started to change. As Norwood Russell Hanson pointed out in his book Patterns of Discovery, educated people no longer saw the sun rise, but the horizon dip5—or so they should have, if they fully absorbed the new theory. Similarly, following Galileo and Newton, knowing observers no longer “saw” projectiles losing speed because impetus, an occult property, was being used up.6 Rather, objects would now remain in a state of rest or in steady, straight movement until they encountered a countervailing force. The physics of the medieval Scholastics, although held to be true for so long, would no longer serve as accepted paradigms. The worlds of nerve physiology and medicine did not, however, change abruptly. A worthy replacement for the existing animal spirit doctrine, a doctrine that had been (p.252) integrated with the rest of the medieval and Renaissance world picture, was decidedly slower in coming. But as the worldview of the new age began to take hold, natural philosophers also began to question time-honored physiological theories and their many implications. Early in the 17th century, the development of new optical instruments, which had such disruptive effects on traditional astronomy, also had a profound influence on the earthly world of things so small that they could not be seen, or at least seen clearly. Simple microscopes showed that nerves are not really hollow, a theory entertained since ancient times, and if anything suggested that their tubes might be filled with a viscous fluid. Similarly, new physiological experiments showed that, when immersed in water and transected, streams of bubbles did not flow out of cut nerves, which earlier had been thought to contain an interior pneumatic wind. Further, when the muscles were more closely examined, researchers found that their volumes did not increase upon contraction, which also should have occurred had they been inflated with a subtle spirit or perhaps injected with some sort of juice. Indeed, the cerebral ventricles, where the spirits were supposedly stored in Galenic physiology, were found to contain nothing more exciting than what seemed to be a water-like fluid. Something was clearly amiss. Seemingly anomalous results, results that could not be explained by the existing animal spirit doctrine and could not easily be explained away, were now emerging—and this kept occurring. These disruptions and challenges to conventional theory helped to set the stage for an upheaval in physiology and medicine, one that would cast the nerves and muscles in a new light.

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Epilogue Still, the needed changes were slow in coming, in part because a good alternative theory was not available. The animal spirit doctrine, now modified to allow nerves to release some sort of a fluid that might in some way stimulate the muscles to contract, would continue to dominate thinking. Indeed, it would manage to hold sway for more than a century after the aforementioned “anomalous” findings first started to make cracks in the old edifice. In fact, animal spirit notions would not really disappear until the 19th century was well underway. In this regard, what took place in physiology contrasts with the rather abrupt upheavals that took place in physics and astronomy after it was revealed that the earth really does revolve around the sun, shattering the enduring ancient idea and conservative church dogma holding that the earth lies at the center of the universe. An analogy can be drawn between the paradigm change revealed by the long history of the animal spirit doctrine and the study of an action potential by the voltage clamp technique. As noted in Chapter 15, the invention of this technique gave researchers a much-needed tool for freezing the millisecond time-scale of the action potential. It thus allowed its various phases to be studied at leisure and in detail. In a similar way the lengthy history of the animal spirit doctrine, with its protracted decline and replacement over several centuries, provides the historian of science an opportunity to study the details of a paradigm change as they occur in slow motion. We have attempted to reconstruct this rich and intriguing time course, placing it in context with chronological tables, short introductory pieces, brief sketches of major figures, and descriptions of the scientific institutions and cultural climates characterizing the different epochs. We found, as hardly needs emphasizing, a myriad of background factors behind the relatively slow changes that occurred. Even during the seemingly static and unyielding Middle Ages, there were, as we have noted in Chapter 5, new ways of viewing living nature, as well as new technologies.7 Gradually, as Alfred (later Lord) Tennyson (1809–1892) wrote at the end of his great poem Morte d’Arthur, “the old order changeth, giving place to new.”8 Natural philosophers began to read the texts of the ancients with increasingly skeptical eyes, and their stances towards the natural world became more and more active. In 1336, the poet Petrarch (1304–1374) climbed Mount Ventoux simply to see what was there and to admire nature from its peak.9 As the centuries passed, natural philosophers turned from observing and contemplating to more active questioning of how things really are. This questioning attitude appeared in many areas of human endeavor as the Middle Ages drew to a close, not only in natural philosophy but also in religion and in the arts.

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Epilogue One particularly important aspect of this change was the emergence of the individual. Dante’s (Durante degli Alighieri; 1265–1321) Divina Commedia, written between 1308 and his death in 1321, is alive with striking figures, both good and evil. By the time of the Reformation, individuals were even more inquisitive, reading books, opening their eyes to the world around them, and making up their own minds on many things. This trend would continue beyond the tumultuous Renaissance, with older animal spirit ideas finding favor with some scholars while being viewed as flawed and in need of repair or even replacement by others. Max Planck (1858–1947), one of the great figures responsible for the comparatively instantaneous paradigm change that took place in early-20thcentury physics, went so far as to suggest that “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up.”10 In other words, as put with more wit, “Science advances one funeral at a time”! This quip, however, seems more than a little over-dramatic when we look back at the animal spirit paradigm. Rather, as we argued above, the change we have traced emerged from a slower and more complex series of advances, with some workers viewing the latest experimental findings as if they were unimportant, while others were attempting to modify the older theory, or to start a new one, which would take the new findings into consideration. These different reactions are significant, and they are one reason why we found the history of the animal spirit paradigm and its eventual replacement is so fascinating, so worthy of tracking. As we close, we wish to express some other personal thoughts and aspirations that we entertained before, while, and after writing this book. Notably, all of us had hoped that (p.253) this voyage into the realm of the animal spirit doctrine, or more accurately doctrines, would serve multiple functions. On one level, we were trying to present readers with the fascinating history of an idea that was at first broadly tied to life itself, and then more specifically to the nervous and muscular systems—a way of thinking that, with various modifications, would survive for more than 2,000 years, spanning cultures, traditions, and empires: an idea about the nerves and muscles that would only grudgingly give way to electrical notions, which would then require further refinements.

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Epilogue And on another level, we were hoping that the material presented here would provide many examples of how new ideas could surface and how changes can take place in the life sciences. In this regard, we tried to write not only about a venerable theory of the past, but also about how adherence to this physiological theory, both with regard to its agent and its structure, generated formidable resistance to alternative ideas. We hope that we have revealed some of the tensions that can exist in the sciences, including how subjective predispositions could affect how people respond to objective data, the importance of both the individual and the group in fostering change, and why certain changes can take time to run their courses. This sampling of an enormous literature with many side branches will surely leave readers with much to think about. To say the least, this also is true for us. We fully recognize that some of what we have encountered and decided to present could be interpreted in different ways, and that our choices of topics, people, and events might not be those that other writers willing to dive into these sometimes murky and even churning waters would select for elaboration. Clearly, different kinds of histories could be constructed about our chosen topic, and there is virtually no limit to the choices and fine details that might be presented in any such endeavor. With these thoughts still very much on our minds, we hope that this book, which caused us to pause and reflect on so many things, will stimulate further scholarship on the pneuma psychikon or spiritus animalis, or what we have more broadly referred to as the animal spirit doctrine, which had once been such an undeniable fact of life, and which dominated physiology in one form or another from ancient times into the 19th century. (p.254) (p.255) Bibliography Bibliography references: [Anonymous] (1669): Steno’s Discours (Book Review). Philosophical Transactions of the Royal Society 5: 1034–1037. [Anonymous] (1745): An historical account of the wonderful discoveries, made in Germany, &c concerning electricity. Gentleman’s Magazine 15: 192–197. Adam C, Tannery P (eds.) (1897–1913): Oeuvres de Descartes. Paris: L.Cerf. Adams G (1792): An Essay on Electricity: Explaining the Principles of the Useful Science and Describing the Instruments…: To which is now added, a Letter to the Author, from Mr. John Birch, Surgeon, on the Subject of Medical Electricity. London, Printed for the author by R. Hindmarsh. Adams WA (1979): The French Garden, 1500–1800. New York, Brazlier.

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Epilogue Adanson M (1757): Histoire Naturelle du Sénégal. Paris, Claude-Jean-Baptiste Bauche. Adanson M (1759): A Voyage to Senegal, The Isle of Goree, and the River Gambia. London, J. Nourse and W. Jonhston [sic]. Adkins AWH (1970): From the Many to the One: A Study of Personality and Views of Human Nature in the Context of Ancient Greek Society, Values and Beliefs. London, Constable. Albert the Great (2008): Questions Concerning Aristotle’s “On Animals”. Resnick IM, Kitchell KF, trans. The Fathers of the Church, Mediaeval Continuation, Washington DC, Catholic University of America Press. Albertus Magnus (1999): On Animals: A Medieval Summa Zoologica (2 vols.). Kitchell KF, Resnick IM, trans., annot. Baltimore, Johns Hopkins University Press. Aldini G (1803): An Account of Late Improvements in Galvanism. London, Printed for Cuthell and Martin…by Wilks and Taylor.…. Aldini G (1804): Essai Théorique et Expérimental sur le Galvanisme. Paris, Imprimerie de Fournier Fils. Alfredi Anglici (1878): Excerpta e libro De Motu Cordis. Barach CS, trans. Innsbruck, Verlag der Wagner’schen Universitaets-Buchhandlung. Algarotti, F (1737): Sir Isaac Newton’s Philosophy Explain’d for the Use of Ladies: In Six Dialogues on Light and Colors. Trans. Carter, E., 1739, (2 vols.) London, Cave. Allamand JNS (1756): Kort verhaal van de uitwerkzelen, welke een Americaanse vis veroorzaakt op de geenen die hem aanraaken. Verhandelingen Hollandsche Maatshappye der Weetenschappen, Haarlem, 2: 372–379. Allen E, Turk JL, Murley R (1993): The Case Books of John Hunter, FRS. London, Royal Society of Medicine. Altenmüller H (1973): Bemerkungen zum Hirtenlied des Alten Reiches. Chronique d’Égypte 48: 211–231. Anderson GT, Anderson DK (1973): Edward Bancroft, M.D., F.R.S., aberrant “practitioner of physick.” Medical History 4: 356–367. Aquinas T (1949): On Spiritual Creatures (De spiritualibus creaturis). Fitzpatrick MC, Wellmuth JJ, trans. Milwaukee, Marquette University Press.

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Epilogue Bacon F (1605): Of the Proficience and Advancement of Learning, Divine and Humane. London, Printed by Thomas Purfoot and Thomas Creede for Henrie Tomes. (In Robertson JM, ed. (1905): Philosophical Works of Bacon. London, Rutledge.) Bacon F (1620): Novum organum. Londini. (In: MJ Adler, ed., trans. (1952): Great Books of the Western World, Vol. 28, Chicago, Encyclopædia Britannica, pp. 107–195; also see Bacon, 2000.) Bacon F (1626): Sylva Sylvarum or A Natural History in Ten Centuries. London, William Lee. Bacon F (1670): Sylva Sylvarum or A Natural History in Ten Centuries (9th edition). London, William Lee. (p.256) Bacon F (2000): The New Organon. L. Jardine and M. Silverthorne, Eds. Cambridge, Cambridge University Press. Baglivi G (1714): Opera omnia medico-practica et anatomica. Lugduni, Anisson & Posuel. Baillet A (1691): La Vie de Monsieur Descartes. Paris, D. Horthmels. (English translation by S R (1693): Life of Monsieur Descartes, Containing the History of his Philosophy and Works. London. Facsimile reprint, Geneva, 1970.) Bancroft E (1769): An Essay on the Natural History of Guiana in South America. London, Becket and De Hondt. (Reprinted by Arno Press & the New York Times, New York, 1971.) Barnes J (1979): The Presocratic Philosophers (2 vols.). London, Routledge & Kegan Paul. Bastholm E (1950): The History of Muscle Physiology. From the Natural Philosophers to Albrecht von Haller. København, Ejnar Munskgaard. Bastholm E (1968): Niels Stensen’s Myology. Analecta Historico-Medica 3: 147– 153. Bataille B, Wagner M, Lapierre F, Goujon JM, Buffenoir K, Rigoard P (2007): The significance of the rete mirabile in Vesalius’s work: an example of the dangers of inductive inference in medicine. Neurosurgery 60: 761–768. Bayon HP (1938): William Harvey, physician and biologist: his precursors, opponents and successors. Part III. Annals of Science 3: 435–456. Beare JI (1906): Greek Theories of Elementary Cognition from Alcmaeon to Aristotle. Oxford, Clarendon Press.

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Epilogue Beaudreau SA, Finger S (2006): Medical electricity and madness in the 18th century: the legacies of Benjamin Franklin and Jan Ingenhousz. Perspectives in Biology and Medicine 49: 330–345. Bedini SA (1964): The Role of Automata in the History of Technology. Technology and Culture 5: 24–42. Bell C (1811): Idea of a New Anatomy of the Brain. London, Strahan and Preston. (Reprinted in PF Cranefield, The Way in and the Way Out, Mount Kisco (NY), Futura Publishing Co., pp. 3–36.) Bell C (1826): On the nervous circle which connects the voluntary muscles with the brain. Philosophical Transactions of the Royal Society of London 116: 163– 173. Belloni L (1968): Die Neuroanatomie von Marcello Malpighi. Analecta Medico Historica 3: 193–206. Belon P (1553): Petri Bellonii cenomani de aquatilibus libri duo cum inconibus ad vivam ipsorum effigem quoad eius fieri potuit expressis. Parisiis, Apud Carolum Stephanum. Belt E (1956): Leonardo the Anatomist. Lawrence, University of Kansas Press. Benz E (1948/2002): Emanuel Swedenborg. Visionary Savant in the Age of Reason. Nicholas Goodrick-Clarke, trans. West Chester, Swedenborg Foundation. Berengario da Carpi (1522/1959): A Short Introduction to Anatomy (Isagogae breves). Lind LR, trans. Chicago, Chicago University Press. (Originally published in 1522) Berg A (1942): Die Lehre von der Faser als Form- und Funktionelement des Organismus. Virchow Archiv 309: 333–460. Bernstein J (1868): Über den zeitlichen Verlauf der negativen Schwankung des Nervenstromes. Pflüger’s Archiv für der gesamte Physiologie des Menschen under der Tiere 1: 173–207. Bernstein J (1871). Untersuchungen über den Erregungsvorgang im Nerven und Muskelsystem. Heidelberg, C. Winter. Bernstein J (1902): Untersuchungen zur Thermodynamik der bioelektrischen Ströme. Pflüger’s Archiv für der gesamte Physiologie des Menschen under der Tiere 92: 521–562. (English translation in Boylan JW, ed. (1971): Founders of Experimental Psychology. München, J. F. Lehmanns Verlag, pp. 258–299.)

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Epilogue Bernstein J (1912): Elektrobiologie: Die Lehre von den elektrischen Vorgängen im Organismus auf moderner Grundlage dargestellt. Braunschweig, Vieweg & Sohn. Berryman S (2002): Aristotle on pneuma and animal self-motion. Oxford Studies in Ancient Philosophy 23: 85–97. Bertholon P (1780): De l’Électricité du Corps Humain Domain dans l’Etat de Santé et de Maladie. Paris, Chez Didot. Bertholon P (1786): De l’Électricité du Corps Humain Domain dans l’Etat de Santé et de Maladie, 2nd ed. (2 vols.). Paris, Croulbois/Lyon, Bernuset. Bertucci P (2001a): The electrical body of knowledge: Medical electricity and experimental philosophy in the mid-eighteenth century. In Bertucci P, Pancaldi G, eds., Electric Bodies: Episodes in the History of Medical Electricity. Bologna, Università di Bologna, pp. 43–68. Bertucci P (2001b): A philosophical business: Edward Nairne and the patent medical electrical machine (1782). History of Technology 23: 41–58. Bertucci P (2006): Back from wonderland: Jean Antoine Nollet’s Italian tour (1749). In Evans RJW, Marr A, eds., Curiosity and Wonder from the Renaissance to the Enlightenment. Aldershot, Ashgate Publishing Ltd., pp. 193–211. Bertucci P (2007): Viaggio nel paese delle meraviglie: Scienza e curiosità nell’Italia del Settecento. Torino, Bollati Boringhieri. Bertucci P, Pancaldi G. (Eds.) (2001): Electric Bodies. Bologna, Università di Bologna. Bidloo G (1685): Anatomia humani corporis. Amsterdam, Someren, Dyk and Boom. Birch T (1756): [Untitled note about a presentation by Dr. (Jonathan) Goddard before the Royal Society on December 16, 1669 “to shew [sic], whether the muscles of an animal, in their motion, are bigger or less in their total sum of dimensions?,” demonstrating that muscle volume decreases slightly rather than increasing upon contraction.] In The History of the Royal Society of London for Improving of Natural Knowledge from its First Rise, Vol. 2. London, A. Millar in the Strand, pp. 411–412. Boerhaave H (1731): Oratio de honore medici servitute. Leiden, Severinus. Boerhaave H (1735): Elements of Chemistry: Being the Annual Lectures of Herman Boerhaave. Translated from the Original Latin by Timothy Dallowe, Vol. I. London, J and J Pemberton, J Clarke, A Millar, J Gray. Page 11 of 54

Epilogue Boerhaave H (1735–1737): Praelectiones publicae de corde. Leiden, University Library MS. Boerhaave H (1737): Aphorismi de cognoscendis et curandis morbis in usum doctrinae domesticae digesti. Editio Leydensis quinta auctior. Lugduni Batavorum, Haak, Luchtmans, Verbeek, et Rotterodami, Beman. Boerhaave H (1742–46): Dr. Boerhaave’s Academical Lectures on the Theory of Physic, Being a Genuine Translation of his Institutes and Explanatory Comment, Collated and Adjusted to Each Other, as They were Dictated to his Students at the University of Leyden (Institutiones medicae) (6 vols.). London, W. Innys. Boerhaave H (1752): Institutiones medicae in usus anuae exercitationis domesticos, digestae ab Hermanno Boerhaave. Edinburgh, Apud, T. & W. Ruddimannos; A. Kincaid & A. Donaldson. Boerhaave H (1959): Praelectiones de morbis nervorum 1730–1735. Schulte BPM, ed., trans. (into German). Leiden, E. J. Brill. Boerhaave H, Albinus BS (1725): [Andreas Vesalius] Opera omnia anatomica et chirurgica. Cura Hermanni Boerhaave…et Bernhardi Siegfried Albini…. Lugduni Batavorum, Apud Joannem du Vivie & J. & H. Verbeek. Boerner P (1981): Johann Wolfgang von Goethe 1832/1982: A Biographical Essay. Bonn, Inter Nationes. Bono JJ (1984): Medical spirits and the medieval language of life. Traditio 40: 91–130. Bono JJ (1990): Reform and the Languages of Renaissance Theoretical Medicine: Harvey versus Fernel. Journal of the History of Biology 23: 341–387. Bono JJ (1995): The Word of God and the Languages of Man: Interpreting Nature in Early Modern Science and Medicine: Ficino to Descartes. Madison, University of Wisconsin Press. (p.257) Boorstein D (1983): The Discoverers. New York, Random House. Booth NB (1960): Empedocles account on breathing. Journal of Hellenic Studies 80: 10–15. Borelli GA (1680–81): De motu animalium (2 vols.). Roma, Bernabò. (Trans. in Borelli GA (1989): On the Movement of Animals. Maquet P, trans. Berlin/New York, Springer-Verlag.) Bossi L (2003): Histoire Naturelle de l’Âme. Paris, Presses Universitaires de France.

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Epilogue Bourignon A (1703): The Light Risen in Darkness in Four Parts (Being a Collection of Letters). London, Manship, Parker and Newman. Bowers JZ, Carrubba RW (1970): The doctoral thesis of Engelbert Kaempfer. Journal of the History of Medicine and Allied Sciences 25: 270–310. Boyle R (1688): A Disquisition on the Causes of Natural Things. London, Taylor. Brands HW (2002): The First American. New York, Anchor Books. Brazier M (1984): A History of Neurophysiology in the 17th and 18th Centuries. New York, Raven Press. Bréhier É (1950): Les Idées Philosophiques et Religieuses de Philon d’Alexandrie. Paris, Vrin. Bremmer JN (1983/1993): The Early Greek Concept of the Soul. Princeton, Princeton University Press. Bresadola M (1997): La biblioteca di Luigi Galvani. Annali di Storia delle Università Italiane 1: 167–197. Bresadola M (1998): Medicine and science in the life of Luigi Galvani (1737– 1798). Brain Research Bulletin 46: 367–380. Bresadola M (2008a): Animal electricity at the end of the eighteenth century: the many facets of a great scientific controversy. Journal of the History of Neurosciences 17: 8–32. Bresadola M (2008b): L’elettricità contesa: Luigi Galvani, Alessandro Volta e la nascita dell’elettrofisiologia moderna. In M. Piccolino (ed.), Neuroscienze Controverse. Torino, Bollati Boringhieri. Brett GS (1921): A History of Psychology. (2 vols.) London: George, Allen and Unwin. Brewster D (1855): Memoirs of the Life, Writings and Discoveries of Sir Isaac Newton. (2 vols.) Edinburgh. Brian P (1979): Galen on the ideal physician. South African Medical Journal 52, 936–938. Brown TM (2008): Bellini, Lorenzo. In Gillispie CC, ed. Complete Dictionary of Scientific Biography, Vol. 1. New York, Charles Scribner’s Sons, pp. 592–594. Brydone P (1757): An instance of the electrical virtue in the cure of a palsy. Philosophical Transactions of the Royal Society of London 50, pt. 1: 392–395.

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Epilogue Buranelli V (1975): The Wizard from Vienna. New York, Coward, McCann and Geoghagen. Burckhardt J (1945): The Civilisation of the Renaissance. Middlemore SGC, trans. London, Phaidon Press. Burnett Ch, Jacquart D (1994), eds.: Constantine the African and ‘Ali ibn al-’Abbâs al-Magûsî: The Pantegni and related texts. Studies in Ancient Medicine, vol. 10 (ed. John Scarborough). Leiden, E. J. Brill. Burton W (2nd ed., 1746): An Account of the Life and Writings of Herman Boerhaave, Doctor of Philosophy and Medicine, Professor of the Theory and Practice of Physic…in the University of Leyden. London, H. Lintot. Burtt EA (1932): The Metaphysical Foundations of Modern Physical Science. London, Routledge and Kegan Paul. Caldani LMA (1757): Sur l’insensibilité et l’irritabilité de Mr. Haller. Seconde lettre de Mr. Marc Antoine Caldani. In Haller A von, Mémoires sur la Nature Sensible et Irritable des Parties du Corps Animal, Vol III. Lausanne, M.-M. Bousquet, pp. 343–490. Canton J (1753): Electrical experiments with an attempt to account for their several phaenomena. Philosophical Transactions of the Royal Society of London 48: 350–358. Canton J (1754): Concerning some new electrical experiments. Philosophical Transactions of the Royal Society of London 48: 780–785. Carruba RW, Bowers JZ (1982): Engelbert Kaempfer’s first report of the torpedo fish of the Persian Gulf in the late seventeenth century. Journal of the History of Biology 15: 263–274. Caton R (1875): The Electrical Currents in the Brain. British Medical Journal 2: 278. Cavendish H (1776): An Account of some attempts to imitate the effects of the torpedo by electricity. Philosophical Transactions of the Royal Society 66: 196– 225. Celsus AC (1935): De medicina (On Medicine). Spencer WG, ed. trans. London, Heinemann, Loeb Classical Library. Cheyne G (1733): The English Malady; Or a Treatise of Nervous Diseases of all Kinds,…. London, Printed for G. Strahan, and J. Leake at Bath. Clark K (1958): Leonardo da Vinci. Harmondsworth, Penguin Books.

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Epilogue White L Jr. (1963): What accelerated technological progress in the Western Middle Ages? In Crombie AC, Scientific Change. London, Heineman. Whitehead AN (1942): Adventures of Ideas. Harmondsworth, Penguin Books. Whitteridge G (1959): William Harvey’s De Motu Locali Animalium 1627. Cambridge, Cambridge University Press. Whytt R (1751/1768): An Essay on the Vital and Other Involuntary Motions of Animals. Edinburgh, Hamilton, Balfour and Neill. In The Works of Robert Whytt, M.D., Published by his Son. Edinburgh, Beckett, Hondt and Balfour, pp. 1–208. Whytt R (1755/1768): Observations on the Sensibility and Irritability of the Parts of Men and other Animals, Occasioned by the Celebrated M. de Haller’s Late Treatise on Those Subjects. Edinburgh, Balfour. In The Works of Robert Whytt, M. D., Published by his Son. Edinburgh, Beckett, Hondt and Balfour, pp. 255– 306. Willcox W (1983): The Papers of Benjamin Franklin, Vol. 23. New Haven, Yale University Press. Williamson H (1775): Experiments and observations on the Gymnotus Electricus, or electrical eel. Philosophical Transactions of the Royal Society 65: 94–101. Willis T (1664): Cerebri anatome. Londini, Typis Ja. Flesher, Impensis Jo. Martyn & Ja Allestry apud insigne Campanae in Coemeterio. (Also see Willis, 1681, 1965) Willis T (1672): De anima brutorum. Londini, Typis E.F. impensis Ric. Davis, Oxon. (Also see Willis 1683) Willis T (1681): The Remaining Medical Works of that Famous and Renowned Physician Dr. Thomas Willis…Viz I. Of Fermentation. II. Of Feavours. III. Of Urines. IV. Of the Ascension of the Bloud. V. Of Musculary Motion. VI. Of the Anatomy of the Brain. VII. Of the Description and Uses of the Nerves. VIII. Of Convulsive Diseases…. London, Printed for T. Dring, C. Harper, J. Leigh, and S. Martyn. Willis T (1683): Two Discourses Concerning The Soul of Brutes, Which is that of the Vital and Sensitive of Man. Pordage S, trans. London, Dring, Hayes and Leigh. (Originally published in 1672 as De anima brutorum.) Willis T (1689): The London Practice of Physick. London, Basset, Dring and Harper. Willis T (1965): The Anatomy of the Brain and Nerves with a Note on Pordage’s English Translation. Feindel W, ed. Montreal, McGill University Press. Page 52 of 54

Epilogue Wilson LG (1959): Erasistratus, Galen and the Pneuma. Bulletin of the History of Medicine 33: 293–314. Wood GS (2004): The Americanization of Benjamin Franklin. New York, Penguin Press. Young JZ (1936a): Structure of nerve fibres and synapses in some invertebrates. Cold Spring Harbor Symposia on Quantitative Biology 4: 1–6. Young JZ (1936b): The structure of nerve fibres in cephalopods and crustacea. Proceedings of the Royal Society of London, ser. B, 121: 319–337. Young JZ (1936c): The giant nerve fibres and epistellar body in cephalopods. Quarterly Journal of Microscopical Science 78: 367–386. Zett L (1983): J. Bernstein—Leben, Persönlichkeit und wissenschaftliches Werk. In Zett L, Nilius B, eds., Bernstein Symposium 1981. Beiträge zur Universitätsgeschichte der Martin-Luthor-Universität Halle-Wittenberg 32. Halle a. d. Saale, pp. 7–22. Ziggelaar A (1997): Chaos: Niels Stensen’s Chaos-Manuscript, Copenhagen, 1659. Copenhagen, The Danish National Library of Science and Medicine. Zimmer C (2004): Soul Made Flesh: Thomas Willis, The English Civil War and the Mapping of the Mind. London, Heinemann. Zysk KG (2007): The bodily winds in ancient India revisited. Journal of the Royal Anthropological Institute 13: S105. Notes:

(1) Stensen, 1669; 1733 trans., 1950 ed., p. 1. (2) Kuhn, 1962, p. 23. (3) Whitehead, 1942. (4) Kuhn, 1962. Kuhn’s theory of paradigm change has been criticized by some subsequent philosophers of science. In a later essay, he partially withdrew the term, replacing it with “disciplinary matrix…the common or shared possession of the community” (Kuhn, 1977, p. 463). For our purposes, however, the term “paradigm” and “paradigm change” is simpler and more serviceable. (5) Hanson, 1958, p. 5. (6) An excellent account of impetus theory and its demise is to be found in Crombie, 1961, vol. 2, p. 59ff. (7) White, 1963. Page 53 of 54

Epilogue (8) Tennyson, 1911, p. 129. “The old order changeth, giving place to new…/Lest one good custom should corrupt the world.” Tennyson is believed to have written Morte d’Arthur as early as 1835. (9) Petrarch, 1336. Petrarch does not seem to have been the first to climb the mountain in medieval times, but his account of his experience and his aesthetic response to the scenery visible from its peak have conventionally been taken to signal a new attitude to the natural world. Before his time, the wild places of the world were avoided as the haunts of evil spirits. (10) Planck, 1949, pp. 33–34.

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Index

The Animal Spirit Doctrine and the Origins of Neurophysiology C.U.M. Smith, Eugenio Frixione, Stanley Finger, and William Clower

Print publication date: 2012 Print ISBN-13: 9780199766499 Published to Oxford Scholarship Online: September 2012 DOI: 10.1093/acprof:oso/9780199766499.001.0001

(p.269) Index Abbas, Haly writings, Complete Book of the Medical Art (Liber totius medicinae), 65, 67, 67f Abu Yahya Zakariya’ ibn Muhammad al-Qazīnī, 214 Academia della Fucina, 132, 133 Academical Lectures on the Theory of Physic (Boerhaave), 157, 161, 162f, 191 Academy of Athens, 17, 20 Accademia degli Investiganti, 133 Accademia del Cimento, 224 action potential. See nerves Adanson, Michel writing, Histoire Naturelle du Sénégal, 226 Adkins, A. W. H., xii–xiii aether, 22, 148–49, 172, 211 afterlife, pneuma and, 46 Age of Enlightenment, 143, 157 Age of Faith, animal spirit in, 71–91 air (aer), 11, 13 within body, 14–16 pneuma as, 11 from, 35 Albertus Magnus (Albert the Great), xi, 42, 43, 74–75, 75f brain studied by, 76, 76f theory of cerebral ventricles (“cells”), 76, 76f writing, Philosophia naturalis, 76, 76f Alcmaeon of Croton, 13, 14, 21, 24, 26, 32, 49 Aldini, Giovanni, 240, 240f, 240nn30–31, 241f Alexander the Great, 20, 26, 29, 45, 59 Alexandria, 6, 26 research institute at, 29–30 Royal Library at, 30f Page 1 of 30

Index Alexandrian neurophysiology, 30 Alfanus, 73 Algarotti, Francesco writings, Sir Isaac Newton’s Philosophy Explain’d for the Use of Ladies, 148 Alhazen. See al-Haytham Allamand, Jean Nicolas Sébastien, 204, 227, 227f Almagest (Ptolemy), 61, 63 American Philosophical Society, 208, 231 Anathomia (Nicolai), 72, 72n3, 80 Anathomia corporis humani (Mondino de Luzzi), 44, 80, 80f, 81, 84 Anatomia hepatis (Glisson), 128 Anatomia plantarum (Malpighi), 117 anatomical drawings, 81n61, 81–84, 82f, 83f Anatomie des plantes (Grew), 116 “Anatomy Lesson of Dr. Nicolaes Tulp” (Rembrandt), 100, 101f, 102 Anatomy of the Brain and Nerves (Willis), 137 anatomy rebirth, 79–81 Anaxagoras of Clazomenae, 14, 16, 17 Anaximander of Miletus, 12 Anaximenes of Miletus, 9, 11, 15, 26, 33 anima, 5, 26–27. See also biblical anima-spirit Boerhaave’s theory of, 160f, 160–65, 161n28, 161nn25–26, 170 in full charge of body, 157–58 animae spiritus, 192 animal electricity of, 199, 216–17, 221–34 du Bois-Reymond’s study of, 245 Galvani’s theory of, 235–40, 236f, 245, 249 natural faculties and, 174–76 pneuma in, 22, 23, 27, 37 vivisections of, 37 animal sentient forces, 192 animal spirit in action, 157–72 in Age of Faith, 71–91 chemical and physical properties (Hoffman), 160 circulation and amount in the body (Boerhaave), 163–65 concept of, 203, 251 decline and fall of, 143 dismissal of, 194–95 doctrine of, 252–53 discarding of, 197–220 establishment of, 39–58 questioning of, 93–108 retreat of, 141–56 health disorders related to (Boerhaave), 165 Hunayn’s writings on, 66–67 invisibility, reasons for (Boerhaave), 163 in Islamic medicine, 65–69 Page 2 of 30

Index message-conveying by, 165–66, 166f nature, properties and origin (Boerhaave), 162–63 paradigm of, 238–39 restauration by sleep (Boerhaave), 165 sensation and perception of, 166–67 Swammerdam’s criticism of, 114–15 system malfunction and treatment of, 165 theories of argument and, 127–40 by Boerhaave, 160–70 by Croone, 130–31 by Descartes, 102–7, 109, 173 by Glisson, 180 by Haller, 192 by Harvey, 111 by Hoffmann, 159f, 159–60 by Leibniz, 158f, 158–59 by Monro, 170f, 170–72 by Stahl, 157–58, 158f, 174 by Swedenborg, 171, 171f by Willis, 137–39 animus, 26, 48 antikythera mechanism, 30, 30f Antiochus IV Epiphanes, 45 antiquity rediscovery, 73–74 Aphorisms Concerning the Knowledge and Cure of Diseases (Boerhaave), 184 apoplexy, 16, 165 Aquinas. See Thomas Aquinas Arabic translation, 60–61, 73–74 Aristarchus, 30 Aristocles. See Plato Aristotelian philosophy, 88 Aristotle, xi, 9, 11n4, 12, 19f, 20f Harvey influenced by, 110–12 impact of, 74–75, 77 Lyceum of, 19–21, 20n51, 22, 29, 31 philosophy after, 23–26 soul concept of, 21–22, 23, 26, 27, 47, 174 theories of animal movement, 23 works of, 21, 23, 42, 60, 65, 78 writings Movement of Animals (De motu animalium), 23n73, 78 Progression of Animals (De incessu animalium), 23 On the Soul (De anima), 21, 23, 174n6 arteries, pneuma in, 31, 33 Articella, 69, 73 artificial experiments, 237 Art of Medicine (Hunayn), 65, 67 astrology, 62 Page 3 of 30

Index (p.270) The Astronomer (Vermeer), 118 astronomy, 30 Athenagoras of Athens, 47 Athenian philosophy, 29 Athens, 5, 7, 9, 10, 14, 17, 19, 20, 24, 26 atmospheric electricity, 216 atmospheric experiments, 237 atomism, in antiquity, 24–26 atomist, Newton as, 148–49, 149n14 atoms, 162, 184, 184n9 Aubrey, J., 110, 111, 136 Augustine of Hippo (Aurelius Augustinus), 41, 43, 52f, 52–55, 69 spirit and, 53–54 writings, Confessions, 52 Avicenna, xi, 42, 43 brain model of, 72, 73, 74 Islamic ascendancy and, 61, 61f, 65, 67, 68f, 68–69 writings Canon of Medicine (al-Qânûn fī-tibb), 43, 63, 65, 67, 68, 68f, 73, 74 De generatione embryonis, 73f axon. See squid’s giant axon axoplasmic transport, 248 Bacon, Francis, xiii, 42, 88, 89f, 109–10 writings The Advancement of Learning, 97, 109 The Great Instauration, 109, 110n5 Novum organum, 89, 110n5 Bacon, Roger, 73 Baglivi, Giorgio, 179f, 192, 194 fibers categorized by, 179–80 muscle contraction theory of, 180f, 180–81 Baillet, Adrien, 101 Baker, George, 232, 233 Bancroft, Edward, 228n45, 228–29 writings, An Essay on the Natural History of Guiana in South America, 146, 228, 229f Banū Mūsā brothers writings, The Book of Artifices (Kitāb al-Hiyal), 62, 64, 69 baquet, 218, 218f, 218n68 battery electricity and, 207–8, 208n11, 242 Volta’s inventing of, 242 Bayt al-Hikma. See House of Wisdom Beccaria, Giambattista, 195 Becquerel, Antoine Caesar, 243 bees, Swammerdam’s study of, 113 Being, in soul, 18, 26 Bell, Charles writing, Idea of a New Anatomy of the Brain, 242 Page 4 of 30

Index Bellini, Lorenzo, 169 Berengario da Capri, 84f, 84–85 writing, Short Introduction to Anatomy, 84 Bernouili, Johann, 169 Bernstein, Julius writing, Membrantheorie, 247 Bertholon, Pierre, 235 biblical anima-spirit early Christian physiology, 49–51 Jehovah’s breath power, 45–46 New Age, 51–52 resurrection, 46–47 soul of body and, 48–49 spirit and, 47–48 writings about, 52–58 Biographia Literaria (Coleridge), 152 biological Leyden jar, 238 biologist, Harvey as, 110 birds, Galvani’s study of, 236 bladder, 130, 175 blood circulation of, 101, 102, 103–4 movements, 14 pneuma and, 13, 14, 23 as seat of the soul (Harvey), 176 sleep and, 13 as thought, 14–15 vessels, 14, 15, 16, 22 body air within, 14–16 anima in full charge of, 157–58 components of, 13, 19 origin according to Plato, 18 pneuma in, 13, 14, 23 revelation of, 85f, 85–87, 86f soul and, 48–49 Boerhaave, Herman, 144, 153, 160f, 160–70, 173 criticism of others’ theories, 168–70, 183–84 disciples of Fontana, 194–95, 195f Gaub, 187, 187f, 188n34 Gorter, 185f, 185–86, 186f Haller, 155, 189–92, 190f, 190n41, 192f, 194 La Mettrie, 188, 188f, 190, 192 Prochaska, 193f, 193–91 Swieten, 184 Unzer, 192–93, 193f Whytt, 188–89, 189f, 191 Page 5 of 30

Index life and character of, 160–62 medulla described by, 163n44, 163–67, 164f studies of fibers, 184–85, 185f heart, 184, 184n5 muscles, 167–68, 169 optic nerves, 166 supporters and dissenters, 170–71 theories of anima, 160f, 160–65, 161n28, 161nn25–26, 170 nerve juice, 163, 163n33, 164, 252 writings Academical Lectures on the Theory of Physic, 157, 161, 162f, 191 Aphorisms Concerning the Knowledge and Cure of Diseases, 184 Institutes of Medicine, 155 A Method of Studying Physick, 161 bone marrow. See marrow Book of Nature (Biblia naturae) (Swammerdam), 112, 114, 145, 187 The Book of Artifices (Kitāb al-Hiyal) (Banu1 Mu1sā brothers), 62, 64, 69 Borel, Pierre, 178 Borelli, Giovanni, 127, 132–35, 133f, 169, 225 Malpighi and, 133, 134 mathematics taught by, 133 muscle contraction theory of, 133–34 neurophysiology of, 135 propositions of, 134–35 Bougainville, Louis Antoine de, 143 Bourignon, Antoinette, 113, 113nn26–27 bovine muscle study, 119–20, 121f, 122f, 178 brain, 32, 49, 50f, 175–76 Aristotle’s view of, 21 Avicenna’s model of, 72, 73, 74 divisions of, 72, 72f Malpighi’s histology of, 117, 178 mental faculties of, 76, 76f origin according to Plato, 18 studies of by Albertus, 76, 76f by Galen, 50, 53, 66 by Harvey, 112 by Hunayn, 66 by Stensen, 123f, 123–25, 125f by Willis, 137–38 breath, xi, xiin11, 6 of God, 46, 47, 78 pneuma as, 11, 13, 16, 17, 26 Breschet, Gilbert, 243 Caesar, Julius, 30 Calcar, Jan Stephen van, 85, 85n76 Page 6 of 30

Index Caldani, Leopoldo Marc’ Antonio, 194, 236 Canon of Medicine (al-Qânûn fī-tibb) (Avicenna), 43, 63, 65, 67, 68, 68f, 73, 74 Canton, John, 204, 206f cardiovascular system, 32 Cartesians, 104f, 105, 129, 173, 177, 183 Casebook (Willis), 139 Cases of Brain and Nerve Pathologies (Pathologiae cerebri, et nervosi generis specimen) (Willis), 136 catfishes. See electric catfishes Catholic Church, 45 Cavendish, Henry, 230, 231f cell (ventricular) theory of Albertus, 76, 76f medieval, 71–73 cellula logistica, 72 cellula memorialis, 72 cellula phantastica, 72 cellular (ventricular) psychology, 71–74 central nervous system, 176 cerebellum, 49–50 Cerebri anatome (Willis), 136 Chalcidius, 49, 50 Chaos Notebook (Stensen), 121 Christ. See Jesus Christ Christianity, 41, 45, 48, 50, 51–52, 57–58, 59 Christian physiology, early, 49–51 Christian thought about knowledge, 71 about spirit, 71 Christina, Queen, 102, 133 Chrysippus of Soli, 24, 24f, 26 (p.271) Church Fathers, 41, 47 cogitatio, 76 cogito, 100 Cole, Kenneth, 247 Coleridge, Samuel Taylor, 152n32, 152n34, 154 writings, Biographia Literaria, 152 Collège Royale, 99, 101f Collinson, Peter, 209 Commentaries on the Effects of Electricity on Muscular Motion (De viribus electricitatis in motu musculari, Commentaries) (Galvani), 201, 236, 236n6, 237, 238 Commentariolus (Copernicus), 62–63 Commodus, Lucius, 35 Common era, 41 “common sensory” according to Aristotle, 22 according to Boerhaave, 166–67 Complete Book of the Medical Art (Liber totius medicinae) (Abbas), 65, 67, 67f Compositiones medicae (Largus), 214 Page 7 of 30

Index Comprehensive Book on Medicine (al-Nafis), 63, 69 concept of animal spirit, 203, 251 of electric fish, 226–27 of fibers, 128–29, 177–78 of pneuma, 5, 11, 11n6, 88–89 of soul, 21–22, 23, 26, 27, 47, 174 Confessions (Augustine), 52 Conjectures on the Perception, Motion and Generation of Ideas (Conjecturae quaedam de sensu, motu et idearum generatione (Hartley), 151–52, 153 connate pneuma, 22, 23 Constantine I, Roman Emperor, 47, 51, 52f Constantine the African, 65, 69, 73 conversion reaction, 216, 216n55 Cook, James, 143 Copernicus, 30, 127, 251 writings Commentariolus, 62–63 De revolutionibus, 44, 62, 91, 95, 95n1 Copley Medal, 230 cortical glands study, 117–18, 118f Cosmologia sacra (Grew), 116 Croone, William, 127, 129–32, 131f, 131n12, 134, 149, 163 animal spirit theory of, 130–31 bladder studied by, 130 muscle contraction theory of, 131–32, 132f writings, De ratione motus musculorum, 97, 98, 129, 131, 134 Croton, 6, 12, 13, 17 Cunaeus, Andreas, 204 Curtis, Howard, 247 Dante writing, Divina Commedia, 44, 252 Dark Ages, 42, 44, 45, 45n3, 57, 62 Darwin, Erasmus writing, Zoonomia, 143, 201 da Vinci, Leonardo, 42, 78 anatomical drawings of, 81n61, 81–84, 82f, 83f experiments on frogs, 84, 181 Davy, Humphry, 243, 243n45 Davy, John, 243, 243n46 De anima brutorum (Willis), 98, 136, 136n26, 137, 138, 138n41 decline and fall, of animal spirit doctrine, 143 De generatione embryonis (Avicenna), 73f De humani corporis fabrica (Vesalius), 62, 85, 86f, 86–87, 95 Democritus of Abdera, 24–25, 25f De motu animalium (Aristotle), 23, 23n73, 78 De motu animalium (Borelli), 133, 134f De motu locali animalium (Harvey), 111, 112 De motu musculari et spiritibus animalibus (Mayow), 127 Page 8 of 30

Index De naturali parte medicinae (Fernel), 87 De rachitude (Glisson), 128 De ratione motus musculorum (Croone), 97, 98, 129, 131, 134 De rerum natura juxta propria principia (Telesio), 88 De revolutionibus (Copernicus), 44, 62, 91, 95, 95n1 Descartes, René, xi, xiii, xiv, 63, 160, 169 animal spirits theory of, 102–7, 109, 173 in La Flèche, 99, 101f life of, 95, 99–100, 100f neurophysiology of, 100–107, 102n9 blood circulation in, 101, 102, 103–4 heart theory in, 103 muscles in, 101–2, 103f reflex movement in, 104f, 105f, 105–6, 106f, 106nn23–24 soul does not give motion and heat to body, 157, 192 Stensen’s criticism of, 125 writings Discourse on Method, 97, 100n3, 112, 150n21 Excerpta anatomica, 101, 102f L’Homme, 97, 102, 103, 105, 105f, 106, 106f, 107, 123, 130 Le Monde, 45, 97, 100, 102 Passions of the Soul (Passions de l’Ame), 101, 102n8, 104 De symptomatum causis (Galen), 224 De viscerum structura exercitatio anatomica (Malpighi), 98, 117 Dialogues (Plato), 9, 17 digestion, 174 Diogenes of Apollonia, 15, 16, 26, 27 Diogenes of Sinope, 13 Dioscorides writing, Materia Medica, 8, 65 Discourse on Method (Descartes), 97, 100n3, 112, 150n21 dissections of Descartes, 101, 107 of Galen, 36–37, 65, 65n10, 72 of Swammerdam, 112 Divina Commedia (Dante), 44, 252 doctrine. See also animal spirit Hippocratic, 178 du Bois-Reymond, Emil, 244–47 animal electricity studied by, 245 experiments of, 245 molecule research of, 245–46, 246f muscle research of, 245 writing, Untersuchungen über thierische Elektricität, 202, 245 Ductus Stenoniannus, 123 du Fay, Charles François de Cisternay, 209 Early Modern era, xi, xiii, 175 earth, 13, 30 earthquakes, plant electricity and, 211–13 Page 9 of 30

Index Eastern Empire, 59 Ebers’ Papyrus, 223 Edict of Milan, 51 eel. See electric eel Einstein, Albert, 147 electrical experiments, of Franklin, 209 electrical fire, 13, 208, 209 electric catfishes, 221, 222f, 226 electric eel, 199, 221, 222f, 229, 231 electric fish, 203, 211, 213–14, 216n58, 216–17 ancient thoughts about, 222–24, 223f catfishes, 221, 222f, 226 changing opinions of, 227–28 concept of, 226–27 eel, 199, 221, 222f, 229, 231 Malapterurus, 223 mechanical notions about, 224–26 Royal Society and, 224, 226, 228–30, 230f, 232 spark of, 230–34 torpedo rays, 221f, 221–24, 226, 228–30, 230f venom in, 224, 225 Walsh’s theory of, 229–30, 230f, 232 electricity, 199–200. See also medical electricity animal, 199, 216–17, 221–34 atmospheric, 216 battery and, 207–8, 208n11, 242 in heavens, 209–11 as invisible force, 217–19 Leyden jar for, 212, 214, 222, 226–27 machines for, 203–6, 205f, 214 modern history of, 203 nerve, 235–49 plant, 211–13 study of by Franklin, 208f, 208–12, 212f, 222, 229–30, 231, 232, 233 by Haller, 228, 232–33 technology and science of, 203–6 transmission of, 204 Electricology: Or, A Discourse upon Electricity (Turner), 212–13, 213f electrometer, 204 electrotherapists, 215 Elementa physiologiae (Haller), 145, 155, 183, 190f, 191, 192, 228, 244 An Elementary Treatise on Human Physiology (Précis Élémentaire de Physiologie) (Magendie), 243 elements, classic four, 13, 17–18, 18f, 22 embryo, 21, 22 (p.272) Empedocles of Acragas, 13–14, 14n29, 15, 19, 21 energy, xi Enlightenment, 51 Page 10 of 30

Index enormôn, 186–87, 189 Epicureanism, 9, 24, 26, 27, 41, 48 Epicurus of Samos, 24, 25f writing, Letter to Herodotus, 26n89 epilepsy, 15–16 Erasistratean physiological psychology, 33, 34f Erasistratus of Chios, xii, 18n46, 29, 32–34, 33f, 251 cardiovascular system studied by, 32 as physiologist, 32 tubular elements of, 33 vivisection, 32 Eratosthenes, 30 An Essay on the Natural History of Guiana in South America (Bancroft), 146, 228, 229f Etymologies (Etymologiae) (Isidore of Seville), 56 Euclid, 30 Eudemus, 34 Evans, Cadwalader, 216 Excerpta anatomica (Descartes), 101, 102f experimental science method, of Newton, 143 experiments. See also Galvani, Luigi of du Bois-Reymond, 245 of Franklin, 209, 211f of Haller, 189–91, 190n41 kite, 209, 211f metal, 239–42, 240f, 241f of Swammerdam, 113–14, 114f Experiments and Observations on Electricity (Franklin), 145, 201, 211 eyes, as sense-organs, 22 Ezekiel, prophet, 47 Fabricus ab Aquapendente, 110 faculties. See also natural faculties natural and animal, 175 voluntary and involuntary, 163 fantasia, 77 Fernel, Jean, 42, 87f, 87–88, 89, 180 writings De naturali parte medicinae, 87 Universa medicinae, 87 fibers. See also muscle fiber contraction Baglivi’s categories of, 179f, 179–80 Boerhaave’s study of, 184–85, 185f Glisson’s concept of, 128–29, 177–78 irritable, 183–95 fibra motrix, 177 fire, electrical, 13, 208, 209 First Lines of Physiology (Haller), 155 First Lines of Physiology (Primae linae physiologiae) (Haller), 145, 155, 191, 228 fish. See electric fish flesh Page 11 of 30

Index as organ of touch according to Aristotle, 22, 23, 26 according to Nemesius, 49 as protection for the marrow, according to Plato, 18 Fletcher, John writing, Rudiments of Physiology, 245 fluid parts, of human anatomy, 184 Fontana, Felice, 194–95, 195f writing, Laws of Irritability, 194 Francini, Allessandro, 63, 64, 102, 102n11 Francini, Tommaso, 63, 64, 102, 102n11 Franklin, Benjamin, xi American Philosophical Society established by, 208, 231 electricity and, 208f, 208–12, 212f, 222, 229–30, 231, 232, 233 experiments of electrical, 209 kite, 209, 211f honorary degrees awarded to, 210 Library Company of, 209, 209n20 lightning theory of, 209, 211–12, 212f in Royal Society, 210–11, 215 Spencer and, 208–9, 209n17 writings Experiments and Observations on Electricity, 145, 201, 211 The Pennsylvania Gazette, 208 Poor Richard’s Almanack, 208 Franklin square, 209 Frederick II, 80 French Académie Royale des Sciences, 206, 224, 225 frogs experiments on animal electricity, 235–40, 236f, 245, 249, 249n76 artificial, 237 atmospheric, 237 by Leonardo da Vinci, 84, 181 Swammerdam’s study of, 113–14 Gaius, 34 Galen, Claudius, 6, 24, 35f, 41–42, 47, 51, 53, 69, 95, 169 dissections of, 36–37, 65, 65n10, 72 emergence of, 29, 32, 33 physiological psychology of, 35, 36f, 192 studies of brain, 50, 53, 66 muscles, 175–76, 181 pulmonary system, 35 ventricles, 36, 37–38 torpedo rays and, 224 writings, 31, 35 On Anatomical Procedures, 65 Page 12 of 30

Index The best physician must also be a philosopher (Quod optimus medicus sit quoque philosophus), 34 De symptomatum causis, 224 On the Natural Faculties (De naturalibus facultatibus libri tres), 24, 175 On the Usefulness of the Parts of the Body (De usu partium), 29, 66, 66n18, 67 Galileo, xiii, 45, 88, 149, 251 gall bladder, 175, 177 Galvani, Luigi, 236nn6–7 birds studied by, 236 frog experiments of animal electricity, 235–40, 236f, 245, 249, 249n76 artificial, 237 atmospheric, 237 instruments of, 237f Volta’s criticism of, 238n28, 239–42 writing, Commentaries on the Effects of Electricity on Muscular Motion (De viribus electricitatis in motu musculari, Commentaries), 201, 236, 236n6, 237, 238 Garden, Alexander, 231–32 Gardini, Francesco Giuseppe, 235 Gaub, Hieronymus David, 187, 187f, 188n34 Genesis, xi, 45, 46, 47, 54, 55 Gerard of Cremona, 73 German physiological advances of Bernstein, 247 of du Bois-Reymond, 244–47, 246f of Helmholtz, 246f, 246–47 of Hermann, 246–47 of Müller, 244, 244nn51–52 Gibbon, Edward, 143 Gilbert, William, 203–4, 204f Glisson, Francis, 127, 128f, 169 animal spirit theory of, 180 fiber concept of, 128–29, 177–78, 192 irritability theory, 128, 176–78 in Royal Society, 128 on sensation and perception, 128 writings Anatomia hepatis, 128 De rachitide, 128 Goddard, Jonathan, 129, 129f, 132, 169 God’s breath, 46, 47, 78 Gorter, Johannes de, 185f, 185–86, 186f le grand siècle, 127 Gray, Stephen, 204, 206f Gray’s Anatomy, 32 The Great Instauration (Bacon), 109, 110n5 Greeks, 9–11 philosophy of, 9, 10f, 46, 59 Page 13 of 30

Index Gregory of Nyssa, 49 Grew, Nehemiah, 115 microscopic fibers in plants, 178 writings Anatomie des plantes, 116 Cosmologia sacra, 116 Gronov, Laurens Theodor, 227 Guericke, Otto von, 203, 205f Hades, xii, xiif Hadith, 59, 65 Halieutika (Oppian), 224 Haller, Albrecht von, 190f, 195 animal spirit and, 192 concepts of soul, 190–92 experimentation of, 189–91, 190n41 studies of electricity, 228, 232–33 irritability, 190, 194, 236 muscle fiber contraction, 191–92, 192f sensibility, 190 writings Elementa physiologiae, 145, 155, 183, 190f, 191, 192, 228, 244 (p.273) First Lines of Physiology (Primae linae physiologiae), 145, 155, 191, 228 Handbuch der Physiologie des Menschen (Müller), 202, 244 Hanson, Norwood, 251 Hartley, David, 144, 147, 149, 151f, 151n27 vibratory neurophysiology of, 151–55, 155n60, 155n62, 199 writings Conjectures on the Perception, Motion and Generation of Ideas (Conjecturae quaedam de sensu, motu et idearum generatione, 151–52, 153 Observations on Man, 145, 147, 151–52, 152f, 153, 154, 155 Harvey, William, 32, 35, 88, 101, 102, 103 Aristotle’s influence on, 110–12, 176 as biologist, 110 blood as primary seat of soul, 176, 192 as experimentalist, 110 heart studied by, 111 life of, 110f, 110–12 theories of animal spirit, 111 brain, 112 natural faculties, 175 spirit, 111 Hawksbee, Francis, 204, 205f al-Haytham, 65, 67, 150 writing, Optics (Kitāb al Manāzdir), 63, 67 hearing, pneumatic connection to the heart (Aristotle), 22 Page 14 of 30

Index heart, 9 Aristotle’s views in relation to pneuma, 21–22 as “common sensorium,” according to Aristotle, 22 soul and, 22 study of by Boerhaave, 184, 184n5 by Harvey, 111 theory of, 103 heat as component in Epicurean model of soul, 25–26 (hot) in stoic model of soul, 24, 26 as a permeating fluid, 15n32 views of by Aristotle, 21–23 by Heraclitus, 11, 26 hegemonikon, 24, 48, 53 Hellenistic age, 29, 30, 31f Hellenization, 45 Helmholtz, Hermann, 246f, 246–47 Heraclitus, 11–12, 26 Hermann, Ludimar, 246–47 writings, Kernleitertheorie, 247 Herophilus, of Chalcedon, xii, 30, 33f, 49 anatomical structures named by, 31 neuroscience founded by, 31–32 optic nerves studied by, 32, 32n9, 50 Hippocrates of Cos, 15, 15f, 15n36, 65, 169, 223, 223n8 Hippocratic doctrine, 6, 27, 178 Histoire Naturelle du Sénégal (Adanson), 226 History of Animals (Historia animalium) (Aristotle), 23n71, 224 History of Electricity (Priestley), 212 History of Insects (Swammerdam), 113 Hodgkin, Alan, 247, 248, 248f Hoffmann, Friedrich, 159f, 159–60 Holy Spirit, 54 Homer, xii, xiii, xiin10, 33 L’Homme (Descartes), 97, 102, 103, 105, 105f, 106, 106f, 107, 123, 130 L’homme machine (La Mettrie), 145, 188, 188f, 190, 192 Hooke, Robert writing, Micrographia, 97, 115f, 115–16, 116f, 119 Hopkinson, Thomas, 209 House of Wisdom, 60, 61–62, 63 human anatomy rebirth of, 79–81 solid and fluid parts of, 184 human body revealed, 85f, 85–87, 86f Humboldt, Alexander von, 143, 222, 241n36, 241–42, 242f Hunayn, 42, 43, 49, 60, 61 Page 15 of 30

Index animal spirit writings of, 66–67 brain studied by, 66 optic nerves studied by, 65–66, 66f writings Art of Medicine, 65, 67 Ten Treatises on the Structures of the Eye, 62, 65, 66, 67 Hunter, John, 230, 230n57, 231f, 232f Hunter, William, 230 Hutton, James, 143 Huxley, Andrew, 247, 248, 248f Huygens, Christian, 165 iatrophysical theory, 186n17, 186–87 ibn Sina. See Avicenna Idea of a New Anatomy of the Brain (Bell), 242 Il Saggiatore (Galileo), 149 imaginatio, 77 imprensiva, 81 Ingenhousz, Jan, 233 Ingram, Dale, 226, 227 Institutes of Medicine (Boerhaave), 155 intelligence in air Diogenes of Appolonia, 14–15, 27 Hippocratic physicians, 15–16, 27 in man (Aristotle), 21 in universal soul (Plato), 18 invisible force, electricity as, 217–19 Irenaeus of Lugdunum, 47 irritability, 177n34 Glisson’s theory of, 128, 176–78 Haller’s study of, 190, 194, 236 irritable fibers, 183–95 Isidore, of Seville, 55–57, 56f Islamic ascendant/ascendancy, 59–70, 73 Islamic chronology medical developments in, 62t–63t science and technology in, 62t–63t Islamic medicine, animal spirit in, 65–69 Islamic neurophysiology, 65 Islamic science, 41–42, 61–65 Jallabert, Jean, 214 Jehovah’s breath power, 45–46 Jenty, Charles Nicholas, 171–72 Jesus Christ, 41, 46, 47 Jewish beliefs, 45–46, 47 Jewish-Christian tradition, 45, 47 Johannitius. See Hunayn Judgment Day, 41 juice theory, of Boerhaave, 163, 163n33, 164, 252 Page 16 of 30

Index Jundishapur, 60 Kaau-Boerhaave, Abraham, 187 Kaempfer, Englebert, 226 Katz, Bernard, 248 Kepler, xiii Kernleitertheorie (Hermann), 247 King of Macedonia, 19–20, 29 Kinneir, David, 170–71 Kircher, Athanasius, 225 kite experiments, 209, 211f Kleist, Ewald Georg von, 205–6 Koran, 59 Kratzenstein, Christian Gottlieb, 214 Krüger, Johann Gottlob, 214 Kuhn, Thomas, 251n4 writing, The Structure of Scientific Revolution, 251 Lactantius, 47, 51 La Flèche, Descartes in, 99, 101f Laghi, Tommaso, 195 La Mettrie, Julien-Offray de writings L’homme machine, 145, 188, 188f, 190, 192 Natural history of the soul, 188 Largus, Scribonius writing, Compositiones medicae, 214 Latin, Arabic translation into, 73–74 “Law of Specific Nerve Energies” (Müller), 244 law of specific nerve energies, Volta and, 240n29 Laws of Irritability (Fontana), 194 learning chronology, 43–44 Lebenskraft, 244 Leeuwenhoek, Antoni Van. See Van Leeuwenhoek, Antoni Leibniz, Gottfried Wilhelm, 158f, 158–59 Leonardo. See da Vinci, Leonardo Letter to Herodotus (Epicurus), 26n89 Leyden jar biological, 238 electricity stored in, 212, 214, 222, 226–27 Van Musschenbroek’s discovery of, 204–8, 207f Library Company, 209, 209n20 lifting devices, 130f lightning theory, 209, 211–12, 212f Linari, Santi, 243 Linnaeus, Carl von, 143 writing, Systema naturae, 143, 146 lodestone, soul in (Thales), 11, 174 (p.274) London Practice of Physick (Willis), 138n36, 139 Lorenzini, 225, 225n20 Lucretius Carus, Titus, 26 Page 17 of 30

Index Luzzi, Mondino de, 80–81, 84 writings, Anathomia corporis humani, 44, 80, 80f, 81, 84 Lyceum, 19–21, 20n51, 22, 29, 31 machines, for electricity, 203–6, 205f, 214 Magendie, François, 242–43, 243n44 writing, An Elementary Treatise on Human Physiology (Précis Élémentaire de Physiologie), 243 al-Majusi. See Abbas, Haly Malapterurus, 223 Malpighi, Marcello, 115, 116f, 116–18, 169, 181 Baglivi and, 179 Borelli and, 133, 134 brain histology of, 117 cortical glands and fibers studied by, 117–18, 118f, 178, 180 writings Anatomia plantarum, 117 De viscerum structura exercitatio anatomica, 98, 117 al-Ma’mūn Abdallah, 60, 61 Manichaeism, 52, 59 Marat, Jean-Paul, 248–49 writing, A Philosophical Essay on Man, 248 Marcus Aurelius, 35 Marinus, 34 marrow spirit and, 72 universal soul in, 18 Materia Medica (Dioscorides), 8, 65 Mathematical Elements of Natural Philosophy, Confirmed by Experiments: Or An Introduction to Sir Isaac Newton’s Philosophy (Van’s Gravesande), 217 mathematical law, of Newton, 148–49 mathematics, Borelli’s teaching of, 133 Matteucci, Carlo, 243, 244 Mayow, John, 127, 177 mechanical notions, about electric fish, 224–26 mechanizing, of soul, 187–89 medical developments, 62t–63t medical electricity, 215f nerves and, 213–16 torpedinal therapy with, 214, 214n40, 216 medieval cell (ventricular) theory, 71–73 Mediterranean Sea in antiquity (map), 10f medulla, 163n44, 163–67, 164f Membrantheorie (Bernstein), 247 Mémoires pour Servir à l’Histoire des Insectes (Réaumur), 225 memoria, 77 Meno (Plato), 223 mental faculties, of brain, 76, 76f Mersenne, Marin, 100, 100n4 Mesmer, Franz Anton, 217n66, 217–19, 218f, 218n68 Page 18 of 30

Index message-conveying animal spirit, 165–66, 166f metal experiments, 239–42, 240f, 241f A Method of Studying Physick (Boerhaave), 161 Micrographia (Hooke), 97, 115f, 115–16, 116f, 119 microscopy, 115f, 115–16, 119, 119f, 134, 178–79, 252 Middle Ages, xiii, 57, 127, 251, 252 Miletus, 5, 11, 14 Milton, John, xiii miraculous network. See rete mirabile modern history, of electricity, 203 Mohammed, 59, 65 molecule research, 245–46, 246f Le Monde (Descartes), 45, 97, 100, 102 Mondino. See Luzzi, Mondino de Monro, Alexander Primus, 170f, 170–71, 172 Monte Cassino, 69 Morgan, Thomas, 170 mortal soul, 18 Morte d’Arthur (Tennyson), 252, 252n8 motion, as link between soul and body (Stahl), 157 motive spirit, 76 motor proteins, 248 motor systems, 180 motu vitali, 186 Movement of Animals (De motu animalium) (Aristotle), 23n73, 78 Müller, Johannes, 244nn51–52 writings Handbuch der Physiologie des Menschen, 202, 244 “Law of Specific Nerve Energies,” 244 muscle fiber contraction, 191–92, 192f muscles action of, 167–68 of bovines, 119–20, 121f, 122f, 178 contraction theory of Baglivi, 180f, 180–81 Boerhaave, 167–68 Borelli, 133–34 Croone, 131–32, 132f Haller, 191–92 du Bois-Reymond’s research on, 245 general views of Boerhaave, 167–68, 169 Descartes, 101–2, 103f Galen, 175–76 Stensen, 123–24, 124f Van Leeuwenhoek, 119–20, 121f, 122f Muslim conquerors, 60, 60f Muslim empire, 60, 60f al-Nafis Page 19 of 30

Index writings, Comprehensive Book on Medicine, 63, 69 Narmer, 223 natural faculties animal and, 174–76 theories of by Galen, 175 by Harvey, 175 by Vesalius, 176 Natural history of the soul (La Mettrie), 188 natural spirit, 49–50 Nemesian schematic, 72 Nemesius of Emesa, 41, 43, 49–51, 69, 71 writing, On the Nature of Man (De natura hominis), 49, 66n22, 69n35 neo-Platonism, 48, 50, 51 nerves. See also law of specific nerve energies, Volta and forces of, 192 impulses according to Boerhaave, 165–66, 183–84 present theory, 5 medical electricity and, 213–16 optic nerves study of Alcmaeon, 13 of Aristotle, 22 of Boerhaave, 166 of Chalcidius, 49 of Herophilus, 32, 32n9, 50 of Hunayn, 65–66, 66f of Van Leeuwenhoek, 119–20, 120f nerve-actions, 192–93 nerve electricity, 5, 235–49 nerve physiology, 251 nervous system, 5, 79, 79f Nestorian Christian, 60, 60n2 neura, 6, 13, 19, 23 neuroanatomy, in Renaissance, 81–85 New Age, 51–52 New Structure of the Muscles and Heart (Nova musculorum & cordis fabrica) (Stensen), 123 Newton, Isaac, xi, xiii, 18, 147n4, 199 aether of, 148–49 as atomist, 148–49, 149n14 experimental science method of, 143 mathematical law of, 148–49 vibrationism of, 149–51, 169 writings Opticks, 143, 143nn1–2, 144, 145, 146, 147, 148, 149n17, 149–50, 150f, 152, 153, 154, 217 Principia mathematica, 143, 144, 147, 148, 148f, 149 Scholium generale, 147, 148 Page 20 of 30

Index Newton/Hartley vibration theory, 155, 155n60, 169, 199 Nicolai the Physician writing, Anathomia, 72, 72n3, 80 Nobili, Leopoldo, 243, 244 Nollet, Abbé Jean-Antoine, 206–7, 207f, 209, 215, 227 Novum organum (Bacon), 89, 110n5 nucha, 76, 77 Numisianus, 34 Observations on Man (Hartley), 145, 147, 151–52, 152f, 153, 154, 155 Old Testament, 45 On Anatomical Procedures (Galen), 65 On the Nature of Man (De natura hominis) (Nemesius), 49, 66n22, 69n35 On the Soul (De anima) (Aristotle), 21, 23, 174n6 (p.275) On the Usefulness of the Parts of the Body (De usu partium) (Galen), 29, 66, 66n18, 67 Oppian of Corycus writing, Halieutika, 224 Opticks (Newton), 143, 143nn1–2, 144, 145, 146, 147, 148, 149n17, 149–50, 150f, 152, 153, 154, 217 Optics (Kitāb al Manāzdir) (al-Haytham), 63, 67 Overton, Charles, 247 paradigm of animal spirit, 238–39 change in, xi, xin2, 178, 178n48, 251, 251n4 Parmenides of Elea, 12 Passions of the Soul (Passions de l’Ame) (Descartes), 101, 102n8, 104 Patristic literature, 41 Patterns of Discovery (Hanson), 251 Paul Apostle, Saint, 46, 46f, 47, 53 The Pearl of Wisdom (Margarita philosophica) (Reisch), 78, 79f Pelops, 34 The Pennsylvania Gazette (Franklin), 208 perception animalis, 177 naturalis, 177 sensation and, 49, 52, 128, 166–67, 176 sensitiva, 177 perikaryon, 248 peripatetics, 20 Petrarch, 252, 252n9 Philo Judaeus of Alexandria, 46 Philosophia naturalis (Albertus), 76, 76f A Philosophical Essay on Man (Marat), 248 Philosophical Transactions of the Royal Society, 212, 231, 232, 235, 241, 241f philosophy after Aristotle, 23–26 Athenian, 29 Greek, 9, 10f, 46, 59 origins of, 5 Page 21 of 30

Index pre-Socratic, 9–15, 26–27, 41 Scholastic, 42 spread of, 5 Western, 9, 10f phrenitis, 50 physic, psychic and, 168, 173–82 physick, physician, 161 physiological advances. See German physiological advances physiological processes, 174 physiological psychology of Erasistratus, 33, 34f of Galen, 35, 36f physiology early Christian, 49–51 of Hoffmann, 159–60 nerve, 251 new era in, 87–88 solidist, based on fibers (Baglivi), 179 pipette, 14, 14f Planck, Max, 252 plant electricity, earthquakes and, 211–13 Plato, xi, 9, 17f, 19f, 26, 174, 223 Academy, 17–18, 20 Aristocles, 17 sense organs, reason for, 18 souls and, 12, 41, 47 writings Meno, 223 Phaedo, 16 Timaeus, 12, 17, 18, 18f, 19, 21, 49, 66n22, 174 Platonic solids, 17, 18f Platonism, 12, 20 Pliny the Elder, 224, 224n12 Plutarch of Chaeronea, 224 pneuma, xi, xii, xiii, 6, 41 afterlife and, 46 from air, 35 as air in motion or wind, 11 in animals, 22, 23, 27, 37 in arteries, 31, 33 blood and, 13, 14, 23 within body, 13, 14, 23 as breath, 11, 13, 26 composition according to Aristotle, 22 according to Stoics and Epicureans, 24–26 concept of, 5, 11, 11n6, 88–89 connate, 22, 23 definition of, 22, 24 Page 22 of 30

Index as instrument of soul, 22–23, 41 as intelligence, 15–16 as nourishment, 15 properties of, 27, 178 psychic, 29, 33, 37, 49, 50, 51, 251, 252 reservoirs of, 72 through ventricles, 71 pneuma psychikon, 29, 33, 37, 49–50, 163, 251, 252 pneumatic parts, of soul, 24, 48 pneuma zootikon, 29, 33, 36, 37, 163 pnoe, 11, 48 poisson trembleur, 226 Pompey the Great, 46 Poor Richard’s Almanack (Franklin), 208 poroi, 13 Posidonius of Byzantium, 50 powers, of soul, 21 praecordia, 56 prana, xi Praxagoras of Kos, 30–31, 31n4 pre-Socratic philosophers, 9–15, 26–27, 41 Priestley, Joseph, 154, 155n56, 212f writing, History of Electricity, 212 Principia mathematica (Newton), 143, 144, 147, 148, 148f, 149 Pringle, John, 232, 233, 233f Prochaska, Georg, 193f, 193–94 Progression of Animals (De incessu animalium) (Aristotle), 23 propositions, of Borelli, 134–35 prosector, 80f psyche, xi, xii, xiii, 5, 11 psychic, physic and, 168, 173–82 psychic pneuma, 49, 50, 51 psychology, cellular (ventricular), 71–74 psychophysiology, of Albertus, 76–77 Ptolemy, 30 writings, Almagest, 61, 63 pulmonary system, 35 pure animal forces, 192 Pythagoras, 12, 17 Pythagorean school, 13, 17, 19, 26, 41 qi, xi Raphael, 19, 19f, 44, 74 Réaumur, René-Antoine Ferchault de writing, Mémoires pour Servir à l’Histoire des Insectes, 225 Redi, Francesco, 225 reflex movement, 104f, 105f, 105–6, 106f, 106nn23–24 Reisch, Gregor writing, The Pearl of Wisdom (Margarita philosophica), 78, 79f Rembrandt, 100, 101f, 102 Page 23 of 30

Index reminiscientia, 77 Renaissance, xi, xiii, 6, 42, 50, 81–85, 90, 181, 251 reproduction, 22 research Alexandria’s institute for, 29–30 on molecules, 245–46, 246f on muscles, 245 resident spirits, 178 respiration according to Alcmaeon, 13 according to Aristotle, 23 according to Empedocles, 13–14 according to Hippocrates, 15–16 according to Plato, 19 resurrection, 41, 46–47 resuscitation, 136 rete mirabile, 42, 86, 86n84, 87, 163 Rhazes writing, Short Introduction to Medicine, 74 Roman Catholic Church, 45, 58, 127 Romulus Augustulus, 59 Royal Library of Alexandria, 30f Royal Society, 119, 129 electric fish studies and, 224, 226, 228–30, 230f, 232 formation of, 110, 115, 136 Franklin in, 210–11, 215 Glisson in, 128 Stensen in, 125 Van Leeuwenhoek in, 120, 131 Volta in, 239 Walsh in, 229–30, 230f Rudiments of Physiology (Fletcher), 245 Ruhestrom, 245 Salerno, 73, 79–80 saliva, 159 Saul of Tarsus, 46 Scholasticism, 109 Scholium generale (Newton), 147, 148 The School of Athens (Raphael), 19, 19f, 44, 74 Schwankung, 245, 246 science amusements and, 206–8 Islamic, 61–65 (p.276) and learning chronology, 43–44, 97–98, 145–46, 201–2 Newton’s experimental method of, 143 technology and, 62t–63t, 203–6 Scientific Revolution, in 17th century, 51, 224 self-movement, spontaneous, 12, 26 Page 24 of 30

Index Seneca, Lucius Annaeus, 24 sensation and perception, 49, 52, 128, 166–67, 176 senses general, 53 hearing, connected to the heart (Aristotle), 22 smell connected to the heart (Aristotle), 22 pneuma involved in (Alcmaeon), 13 theory of (Boerhaave), 166 touch, flesh as organ of Aristotle, 22, 23, 26 Nemesius, 49 vision, theories of Aristotle, 22 Boerhaave, 166–67 sensibility studies, 190 sensitiva, 177 sensus communis, 76–77, 81, 85, 88 sentient actions, 192 Severus, Septimus, 35 Short Introduction to Anatomy (Berengario da Carpi), 84 Short Introduction to Medicine (Rhazes), 74 Sir Isaac Newton’s Philosophy Explain’d for the Use of Ladies (Algarotti), 148 smell, pneuma involved in according to Alcmaeon, 13 connected to the heart (Aristotle), 22 Socrates, 16f, 16–17, 20, 46, 223 solids in human anatomy, 184 in human body, 178–81 Platonic, 17, 18f soma, 5, 11 soul, 9, 11, 13. See also universal soul according to Plato, 18–19, 47, 69, 69n35 in blood (Harvey), 176 body and, 9, 48–49, 53 concept of, 21–22, 23, 26, 27, 47 after death, 11–12 distinction from spirit, 47–49 essence of, 21 as four elements (Empedocles), 13 heart and, 21, 22 as incorporeal (Nemesius), 51 as intelligent air within body (Diogenes), 14–16 Isidore’s definition of, 57 in lodestone (Thales), 11, 174 main instrument of, 22–23, 41 mechanizing of, 187–89 mortal, 18 Page 25 of 30

Index origin according to Plato, 18 in plants according to Aristotle, 21, 174 according to Plato, 174 according to Pythagoras, 12 pneumatic parts of, 24, 48 powers of, 21 transmigration, 12, 41 criticism by Aristotle, 21 tripartite according to Plato, 18–19, 47, 59, 69n35 criticism by Aristotle, 21 unrelated to motion and heat of the body (Descartes), 157 in ventricles, 32 soul’s higher faculties according to Aristotle, 21 imagination, causes change of body temperature (Aristotle), 23 memory Augustine, 52–53 Nemesius, 49 thought Augustine, 53 Nemesius, 59 South American eel, 231 species sensibilis, 76 Specimen of Elements of Myology (Elementorum myologiae specimen) (Stensen), 123, 124, 124f Spencer, Adam, 208–9, 209n17 Spinoza, Baruch, 161 spirit, xiii, 5–6, 42. See also biblical anima-spirit Augustine and, 53–54 Christian thought on, 71 Harvey’s theory of, 111 Holy Spirit, 54 Hunayn’s writing on, 66–67 marrow and, 72 motive, 76 natural, 49–50 resident, 178 soul and, 47–48 types and properties of (Boerhaave), 162–63 vital, 33, 178 spiritual distress, 191–92 spiritus, 5, 49, 50, 78, 178, 253 spontaneous self-movement, 12, 26 squid’s giant axon, 248 Stahl, Georg Ernst, 144, 157–58, 158f, 174, 181, 192 Steiner, George, 61 Stensen, (Steno) Niels, 120–25, 122f, 122n69, 168 Page 26 of 30

Index brain studied by, 123f, 123–25, 125f muscles studied by, 123–24, 124f, 177 in Royal Society, 125 writings Chaos Notebook, 121 New Structure of the Muscles and Heart (Nova musculorum & cordis fabrica), 123 Specimen of Elements of Myology (Elementorum myologiae specimen), 123, 124, 124f Stoicism, 9, 24, 26, 27, 41, 46, 48, 144, 175 stomach, 175 Straton of Lampsacus, 31 The Structure of Scientific Revolution (Kuhn), 251 subtle fluids, vibrations and, 147–56 succus nerveus, 131, 132, 135 Summa Theologica (Aquinas), 43, 75 Swammerdam, Jan, 169, 187 animal spirit criticized by, 114–15 bees studied by, 113 dissections of, 112 experiments of, 113–14, 114f, 181 frogs studied by, 113–14 writings Book of Nature (Biblia naturae), 112, 114, 145, 187 History of Insects, 113 Swedenborg, Emanuel, 171, 171f Swieten, Gerhard van, 184 Swift, Jonathan, xiv Sydenham, Thomas, 169 Syriac, 59 Systema naturae (Linnaeus), 143, 146 Tabulae anatomicae sex (Vesalius), 44, 85, 86 Tatian the Assyrian, 48 technology, science and, 62t–63t, 203–6 Tegni, 65 Telesio, Bernardino, 42, 88–90, 89f Tennyson, Alfred writing, Morte d’Arthur, 252, 252n8 Ten Treatises on the Structures of the Eye (Hunayn), 62, 65, 66, 67 Tertullian of Carthage, 48–49, 51 Thales of Miletus, 5, 11, 26, 27, 47, 174 Theophrastus of Eresus, 13 theories. See also animal spirit; Boerhaave, Herman; cell (ventricular) theory; natural faculties of brain, 112 of heart, 103 iatrophysical, 186–87 of irritability, 128, 176–78 of lightning, 209, 211–12, 212f Page 27 of 30

Index medieval three cell, 49–50, 50f, 73 of muscle contraction, 131–32, 132f, 133–34, 180f, 180–81 Pythagorean, 13, 19, 26 of soul, 57 of ventricles, 76 of vibrations, 155, 155n60, 199, 203 of Walsh, 229–30, 230f, 232 Theory of the Earth (Hutton), 143 Thessalonians 1 (Paul), 47 Thévenot, Melchisédec, 122, 125 Thomas Aquinas, 42, 74–75, 75f, 77–78 writing, Summa Theologica, 43, 75 Thomism, 75 Thomist synthesis, 77–78 three cell (cellae) theory of the brain, medieval according to Albertus Magnus, 76, 76f according to Augustine of Hippo, 41, 52–53 according to Nemesius, 41, 49–51 thymos, xiii Timaeus of Locrii, 17, 18 Tomb of Ti, 223, 223f, 223n4 torpedinal therapy, 214, 214n40, 216 (p.277) torpedo rays, 221f, 221–24, 226, 228–30, 230f, 243 touch, flesh as organ of according to Aristotle, 22, 23, 26 according to Nemesius, 49 tourmaline, 238, 238n16 transmembrane flows, 248, 248n74 transmission, of electricity, 204 Trattato dell’Arco Conduttore, 240 tripartite soul, 18–19, 47, 69, 69n35 tubular elements, in early anatomy, 33 Tubuli, 163–64 Turner, Robert, 216, 226 writings, Electricology: Or, A Discourse upon Electricity, 212–13, 213f Two Medico-Philosophical Arguments (Diatribe duae medico-philosophicae) (Willis), 136 universal soul composition according to Plato, 18, 26 as destiny of souls, 41 intelligence in, 18 Universa medicinae (Fernel), 87 Untersuchungen über thierische Elektricität (du Bois-Reymond), 202, 245 Unzer, Johann August, 192–93, 193f Upanishads, xi Van der Lott, Frans, 227 Van Leeuwenhoek, Antoni, 115, 118f, 118–20, 126, 131n16, 169 in Royal Society, 120, 131 studies of Page 28 of 30

Index bovine muscle, 119–20, 121f, 122f, 178 optic nerves, 119–20, 120f Van Musschenbroek, Pieter, 204–8, 207f Van’s Gravesande, Laurens Storm, 227 Van’s Gravesande, Willem Jacob writing, Mathematical Elements of Natural Philosophy, Confirmed by Experiments: Or An Introduction to Sir Isaac Newton’s Philosophy, 217 Vatican, 58 venom, 224, 225 ventricles Albertus Magnus’s theory of, 76 da Vinci’s drawings of, 82f, 83f pneuma through, 71 soul in, 32 studies of by Galen, 36, 37–38 by Vesalius, 86, 86f Vermeer, Johannes, 118, 118n57 Verus, Lucius, 35 Vesalius, Andreas, xi, 35, 42, 43, 90, 163 human body revealed by, 85f, 85–87, 86f natural faculties and, 176 writings De humani corporis fabrica, 62, 85, 86f, 86–87, 95 Tabulae anatomicae sex, 44, 85, 86 vibrationism demise of, 155–56 of Newton, 149–51, 169 vibrations associations and, 154–55 Newton/Hartley theory of, 155, 155n60, 199 subtle fluids and, 147–56 theories of, 203 vibratory neurophysiology, of Hartley, 151–55, 155n60, 155n62, 199 vision Alcmaeon, theory of, 12 Aristotle, theory of, 21, 22 Plato, need of, 18 vis nervosa, 192–94 vital spirits, 33, 178 vivisections of animals, 31, 32, 37, 85, 86 of humans, 32, 85 Volta, Alessandro, 235 battery invented by, 242 Galvani criticized by, 239n28, 239–42 law of specific nerve energies and, 240n29 metal experiments of, 239–42, 240f, 241f in Royal Society, 239 Page 29 of 30

Index voltage clamp technique, 248 Voltaire, 148 Walsh, John Copley Medal won by, 230 electric fish theory of, 229–30, 230f, 232 in Royal Society, 229–30, 230f water, 11, 13 Western Empire, 59 Western philosophy, 9, 10f Western tradition, xi, xii, xiii Whitehead, Alfred, 18 Whytt, Robert, 188–89, 189f, 191 Wilkins, John, 129 Willem of Moerbeke, 73, 74 Williamson, Hugh, 231 Willis, Thomas, xiii, 35, 95, 125, 127, 135f, 135–39, 169 animal spirit theory of, 137–39 brain studied by, 137–38 resuscitation performed by, 136 writings Anatomy of the Brain and Nerves, 137 Casebook, 139 Cases of Brain and Nerve Pathologies (Pathologiae cerebri, et nervosi generis specimen), 136 Cerebri anatome, 136 De anima brutorum, 98, 136, 136n26, 137, 138, 138n41 London Practice of Physick, 138n36, 139 Two Medico-Philosophical Arguments (Diatribe duae medicophilosophicae), 136 wind, 15 Word, 55 Wren, Christopher, 136f Xenophanes of Colofon, 11 Young, John Z., 247 Zeitgeist, 216, 217, 225, 235, 242–43 Zeno of Elea, 12 Zimmermann, Johann, 189 Zoonomia (Darwin), 143, 201 Zoroastrian, 59

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