Chapter 9 Understanding the nervous system in the 18th century

Chapter 9 Understanding the nervous system in the 18th century

Handbook of Clinical Neurology, Vol. 95 (3rd series) History of Neurology S. Finger, F. Boller, K.L. Tyler, Editors # 2010 Elsevier B.V. All rights re...

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Handbook of Clinical Neurology, Vol. 95 (3rd series) History of Neurology S. Finger, F. Boller, K.L. Tyler, Editors # 2010 Elsevier B.V. All rights reserved

Chapter 9

Understanding the nervous system in the 18th century CHRISTOPHER U.M. SMITH* Vision Sciences, Aston University; Universities of Aston and Birmingham, Birmingham, UK

INTRODUCTION The 18th century has often been called the age of “enlightenment” or, in German-speaking regions, Aufklärung. It is the age of Newton, Locke and Hume; of the Encylope´distes, of Voltaire, Lavoisier and Montesquieus’ Lettres Persanes; of Alexander Pope and Samuel Johnson, of Tom Paine and The Rights of Man and, at the end of the century, of Immanuel Kant and transcendental philosophy. It is the age of trade and discovery, of the European diaspora, the age of Bougainville and James Cook and the opening of the world of nature and natural history, an age of collections and above all classification. It is the age of secular history, of Gibbon’s Decline and Fall of the Roman Empire, of the birth pangs of archeology, of dictionaries, of the translation of ancient scripts, of the Rosetta Stone. It is also the age of revolutions – revolutions in the means of production and distribution and of political revolutions in America and later in France. It started as “the age of reason,” where the old systems of belief were subjected to searching scrutiny and ended in the Romantic reaction. It started with the Pope’s view of Nature as a mighty maze but not without a plan, a “great chain of being” where “whatever is, is right.” It ended with the first stirrings of evolutionary ideas, with Erasmus Darwin and Jean Baptiste de Lamarck; ideas which were to lead, in the next century, to the conclusion that whatever is, is far from “necessarily” right but may simply be due to happenstance. All could well have been other than it turned out to be and there is no reason to think, as Leibniz thought, that we live in the best of all possible worlds. It started with monarchy and ended with revolution and then Bonapartism. It is against this background that investigations of the brain and nervous system took place. Although

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diseases of the nervous system had been recognized from the earliest times, it was not until the 18th century that the first glimmerings of a true understanding of the underlying neuroanatomy and neurophysiology became available. Much of this new understanding is associated with the growth of medical schools. The most important of these were located in Paris, London, Leyden, Edinburgh and Bologna. In Paris, Pourfour du Petit (1664–1741), after experience as a military surgeon in the Wars of Spanish Succession, continued his interest in head injuries with pioneering research on the structure and functions of the brain and spinal cord (Pourfour du Petit, 1710). In London, William Hunter (1718–1783), after studying medicine at Edinburgh, opened the famous Great Windmill Street School of Anatomy in 1768. Here he was joined by his younger brother John (1728–1793), and both carried forward extensive research into the nervous system, not only of humans but also of many infra-human animals, and, in so doing, as we shall see below, played important roles in the development of electrophysiological ideas. In Leyden, Hermann Boerhaave (1660–1738), who became known as “Europe’s Teacher,” numbered amongst his pupils some who would become the most prominent names in European neuroscience, Alexander Monro Secundus, John Pringle, William Cullen, Albrecht von Haller, Gerhard van Swieten, and many others, and was instrumental in getting Swammerdam’s Bibjel der Natur published (Boerhaave, 1737/1738). Many of Boerhaave’s pupils came from Scotland and returned to Edinburgh to develop one of Europe’s most prominent centers of teaching and research on the structure and function of the nervous system. Here the Monro dynasty (Primus, Secundus, and Tertius), William Cullen, Robert Whytt and many others not

Correspondence to: C.U.M. Smith, Vision Sciences, Aston University, Birmingham B4 7ET, UK. E-mail: [email protected], Tel: +44-121-454-1443, Fax: +44-121-204-4048.

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only developed scientific knowledge of the system but also taught generations of British and foreign students. Finally, the 18th century, especially toward its end, saw a great efflorescence of neuroscientific research in the ancient University of Bologna. Here Leopoldo Caldani (1725–1813), Felice Fontana (1730–1805) and, most famously of all, Luigi Galvani (1737–1798) and his nephew, Giovanni Aldini (1762–1834), laid the foundations of electrophysiology. It is clear that all of this work cannot be covered in a short chapter. Instead, I intend to focus on progress in understanding the fine structure of the nervous system and the manner in which messages are conducted by the nerves.

HOLLOW NERVES AND THEIR SPIRITS Earlier parts of this book have described the timehonored neurophysiology of the ancients, which was adopted and modified by later scholars, even during the Renaissance. These individuals believed that nerve fibers are tubular structures through which animal spirits travel from brain to periphery and vice versa. Although as long ago as 1543 Vesalius, in his great work on human anatomy, the Fabrica, had doubted the anatomical reality of this belief, the notion lived on well into the 18th century and can still be found in texts published in the middle of the 19th century. Alexander Monro Secundus, for example, devotes several pages to this time-honored, hollow-nerve neurophysiology in his 1783 Structure and Functions of the Nervous System, writing that “Most authors have supposed that the nerves are tubes or ducts carrying a fluid secreted in the brain, cerebellum and spinal marrow” (Monro, 1783, p. 74). Indeed, the old neurophysiology was so well-embedded in the common consciousness that it is often alluded to without comment in 18th-century literature. Tristram Shandy remarks, for instance, on that “very thin, subtle, and very fragrant juice . . . discovered in the cellulae of the occipital parts of the cerebellum” (Book 2, p. 19) and, in an earlier part of his hilarious autobiography, writes: “You have all, I dare say, heard of animal spirit, nine parts in ten of a man’s sense and nonsense . . . depend on its motions and activity” (Book 1, p. 1) (Sterne, 1760). It required both physiological and anatomical research to dislodge the old theories of the human constitution. Furthermore, it was not until the very end of the 18th century that a valid successor theory began to be pieced together. Let us first look at the microscopical evidence.

van Leeuwenhoek. Van Leeuwenhoek sent specimens of a transversely sectioned optic nerve to the Royal Society in 1674 and wrote that, to his great surprise, he could find no cavity: “I solicitously viewed three optic nerves of cows, but could find no hollowness in them” (van Leeuwenhoek, 1675). Van Leeuwenhoek continued his researches into the 1690s, but so strong was the prevailing neurophysiological theory that he speculated that nerves perhaps contained submicroscopic filaments or tubes along which animal spirits might travel: “diverse very small threads or vessels lying close by each other” (van Leeuwenhoek, 1677). The notion that nerve fibers were at some level hollow structures persisted throughout the 18th century, and Ford (2007) has traced it on well into the 19th century, where it is illustrated in a figure in Longet’s Anatomy and Physiology of the Nervous System (Longet, 1842). Microscopes and preparative techniques were just not good enough to prove that nerves did not contain cavities. Indeed, we now know that nerve fibers do contain a viscous fluid – axoplasm, which flows at different rates in both directions within the tubular axon. And, returning to the 18th century, it is not impossible that the great Italian anatomist, Felice Fontana (1730–1805), had observed this viscous fluid in the 1780s. In a letter written to a friend in 1782 he described how, after stripping the sheath from a nerve, he squeezed it between two lenses and observed “une matière glutineuse, élastique, transparente” to exude from the cut end (Fontana, 1784; quoted in Brazier, 1984, p. 146). The microscope, furthermore, sent an ambiguous message. Malpighi’s 1666 microscopy of the mammalian cerebral cortex seemed to show that it consisted of a mass of minute glands (Fig. 9.1) (Malpighi, 1666). This interpretation supported the traditional neurophysiology. The brain filtered an animating principle from the blood and pumped it out via the nerve tubes

THE MICROSCOPE The first practical microscopes were developed at the end of the 17th century by Robert Hooke and Anthony

Fig. 9.1. Malpighi, 1666, De Cerebri Cortice. Malpighi’s picture shows the cerebral “glands” and “fibers.”

UNDERSTANDING THE NERVOUS SYSTEM IN THE 18TH CENTURY to the periphery. William Cullen, Professor of Medicine at Edinburgh from 1747 to 1766, would not have balked at this interpretation: “The most common opinion,” he writes, “is that the brain is a secreting organ, which secretes a fluid necessary to the functions of the nervous system” (Cullen, 1827, vol. 1, p. 118).

SOME CLEVER EXPERIMENTS But if 18th-century microscopes and microscopical techniques were inadequate to settle the question of whether nerves had some element of hollowness, clever experimental techniques began to cast doubt on the idea that the brain secreted an animating principle into the nerves. Jan Swammerdam, in a series of brilliant experiments, had shown as early as 1633 that frog muscles (at least) could be caused to contract when the cut end of the sciatic nerve was stroked or pinched (Fig. 9.2). This seemed to rule out the ancient notion that muscular movement depended on a messenger of some sort sent by the brain down the hollow conduits of the nerves. “From these experiments,” he wrote, “it may, I think be fairly concluded, that a simple and natural motion or irritation of the nerve alone is necessary to produce muscular motion, whether it has its origin in the brain, or in the marrow, or elsewhere.” Although Swammerdam demonstrated his experiments widely to academic audiences and influential visitors (Nordstro¨m, 1954), their implications were so radical that, although widely known, traditional ideas were not dislodged. Swammerdam suggested that spirit or subtle matter flies in an instant through the nerves to the muscles [and] may with the greatest propriety be compared to that most swift motion, which, when one

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extremity of a long beam or board is struck with the finger, runs with such velocity along the wood, that it is perceived almost at the same instant at the other end. (Quoted in Cobb, 2002) But, as already noted, the old time-worn ideas held on tenaciously throughout much of the 18th century. This is an interesting case of a blocked paradigm-change. An anomalous finding, a crucial finding, is consciously overlooked because it cannot be accommodated within the prevailing paradigm. In this case, however, it must be noted that Swammerdam’s work was not published until Boerhaave brought out an edited version in his Bibjel der Natur (Biblia Naturae) over a century later (Boerhaave, 1737/1738; see also Cobb, 2002).

THE IRRITABLE AND SENSITIVE NERVOUS SYSTEM Swammerdam’s notion of irritability was renewed by Francis Glisson at the turn of the century, but it was left to Albrecht von Haller to establish the idea as central to physiological thought. Indeed, in Tissot’s 1755 preface to von Haller’s Dissertation on the Sensible and Irritable Parts of Animals, he lauds him as having made “the great discovery of the present age” (von Haller, 1755, p. iii). Von Haller carried through a vast number of experiments to discover which parts of an animal are “irritable.” He also used a wide variety of stimuli: air puffs, heat, lapis infinalis, oil of vitriol, butter of antimony, touching, squeezing, cutting, burning, etc. He concluded that irritability “does not depend on the nerves, but on the original fabrication of the parts which are susceptible of it” (p. 32). A little further on in the dissertation he homes in on muscle fibers, writing that “there is nothing irritable in the animal but the muscular fibres and the faculty of endeavouring to shorten itself when we touch it is proper to this fibre” (p. 37). Sensibility is, he insists, quite distinct from irritability. Von Haller writes that . . . the sensible parts of the body are the nerves themselves, and those to which they are distributed in the greatest abundance; for by intercepting the communication between a part and its nerve, either by compression, by tying, or cutting, it is thereby deprived of sensation . . . Wherefore the nerves alone are sensible of themselves . . . (von Haller, 1755, p. 31)

Fig. 9.2. Jan Swammerdam (c. 1663). That the drop of water in the capillary tube (e) does not move shows that the frog muscle (b) does not increase in volume when it contracts.

Far from all 18th-century physiologists agreed with von Haller. William Cullen, in particular, who co-founded the medical school in Glasgow and then moved to Edinburgh in 1755 as Professor of Chemistry and later, on the death of Robert Whytt in 1776, as Professor of

110 C.U.M. SMITH the Institutes of Medicine, held that the fine endings of has been remarked that this new preparedness to diagnerve fibers transformed into muscle fibers in a nose nervous debility allowed the growth of a fashionmuscle’s interior. Cullen, indeed, believed that the key able spa society and that tendency to “take the to all diseases lay in the nervous system. His students waters,” so well captured in the 18th-century writings came to call him “Old Spasm” in recognition of his of Samuel Richardson, Brinsley Sheridan, and Tobias teaching that illnesses were caused by a “spasm” or Smollett. disordered reaction of the nervous system. The slow retreat of ancient neurophysiology left a The resolution of the von Haller/Cullen disagreevacuum in medical theory that many sought to fill. If ment awaited, as did so much else in neurophysiology, the nervous system is not the carrier of animal spirit, the improved microscopy of the centuries succeeding and if it is not suitable for the concussive transmission the 18th century. Both agreed, however, that the web envisaged by Swammerdam and others, then how did of nerves was endowed with “feeling.” Robert Whytt, the human organism work? Cullen’s older colleague at Edinburgh, held the same VIBRATIONS AND INVISIBLE, opinion, writing that “we know certainly that the SUBTLE FLUIDS nerves are endowed with feeling” (Whytt, 1765). The notable 18th-century physician George Cheyne, also Many, like David Hartley, felt the influence exerted by educated at Edinburgh, agreed: the great achievements of Sir Isaac Newton (see Smith, 1987). Hartley conceived an associationist psychophysiolFeeling (physical sensibility) is nothing but ogy based on vibrations and vibratiuncles (residual vibraImpulse, Motion or Action of Bodies, gently or tions) in the nerve fibers and white matter of the brain violently impressing the Extremities or Sides of (Hartley, 1749). This notion, although derived from certhe Nerves . . . . (Cheyne, 1733, p. 49) tain speculations found in Newton’s Principia (Newton, 1713, vol. 2, p. 393) and Opticks (Newton, 1717, 2nd LIFE FORCES AND MEDICAL PRACTICES Query), did not find favor with some of the leading The recognition that the nerves are not just inanimate 18th-century physicians and anatomists. Both Boerhaave tubes for transmitting a vivifying spirit from the brain and Monro Secundus believed that the flaccidity of the to the muscles (as Cartesian neurophysiology had nervous system ruled vibrations, even of intraneuronal taught), but sensible in themselves, had an influence particles (as Hartley envisaged), out of court. Later, in on medical practice. Moreover this retreat from the his famous Traité sur le Venin de la Vipère (1781), Felice seeming aridities of Cartesian iatrophysics chimed well Fontana described how he examined nerve “cylinders” with other parts of 18th-century biological thought. In under the microscope and could detect no sign of any 1744, for example, Abraham Trembley had shown that vibration and, like Boerhaave and Monro Secundus, confresh water polyps, such as Hydra, could be subdivided cluded that Hartley’s theory did not accord with the facts. almost indefinitely, and that a new polyp would But if these vibrationist notions found no favor develop from each small fragment (Trembley, 1744). amongst the anatomists, Newton’s other hypothesis, that This was taken by many to imply that the living princiof an all-pervasive “aether” or “subtle fluid,” proved ple was not confined to one or a few organ systems, much more long-lasting. The 18th century was, indeed, but was widely diffused throughout the body. awash with “subtle fluids.” One of the most notorious The´ophile Bordeu (1722–1776) had developed this of these “aetherial” speculations was that initiated and interpretation in his insistence that life is essentially promulgated by Anton Mesmer (1734–1815). Mesmer “sensibilité” (Bordeu, 1774). Indeed he went so far as had qualified in medicine in 1766 with a dissertation to compare a living body to a beehive: a whole com(De Planetarum Influxu in Corporis humanum [The posed of living, sensitive units (see Haigh, 1976). Thus, Influence of the Planets on the Human Body]) on the returning to our subject, it is perhaps not surprising to influence of the heavenly bodies on human well-being. find that the distributed nervous system should have Just as Newton had shown that the planets are held in become far more significant in medical nosology. Thotheir orbits by a mysterious force called “gravity” so, mas Trotter, writing in 1807, observed that at the Mesmer believed, human bodies can be affected by a beginning of the 19th century we do not hesitate to similarly mysterious force, one which he dubbed “aniaffirm that nervous disorders have now taken the mal gravity.” Later, after he was introduced to a new place of fevers, and may justly be reckoned two thirds medical procedure involving the use of magnets by of the whole, with which civilised society is affected.” Father Maximillian Hell, Mesmer changed the name of (Trotter, 1807). Note the word “civilised”: Trotter is his mysterious force to “animal magnetism” (for a full thinking of the upper strata of European society. It account see Lanska and Lanska, 2007).

UNDERSTANDING THE NERVOUS SYSTEM IN THE 18TH CENTURY In essence Mesmer believed that good health depended on the free flow of life processes throughout the body’s innumerable channels. When, for one reason or another, these channels were blocked, this flow was impeded and illness resulted. In 1774, he successfully treated a patient by getting her to swallow a solution containing iron and then attaching magnets to various parts of her body. Later he dispensed with magnets and alleged the cures could be achieved by the physician directly controlling the mysterious magnetic effluvium. He was unable, however, to convince his fellow physicians, in particular Jan Ingenhousz, of the validity of his treatment and had to leave Vienna for Paris. Here he was successful in building up a substantial practice and even developed a special tub, the baquet, which he regarded as equivalent to the electrician’s Leyden jar, for concentrating the magnetic aether. Numerous patients could sit around Mesmer’s baquet and simultaneously experience the magnetic cure. However, nemesis awaited in the form of a Royal Commission set up by King Louis XVI in 1784, and headed by the American ambassador and natural philosopher, Benjamin Franklin. The Franklin commission comprehensively disproved Mesmer’s practice and showed that the undoubted effects, and sometimes cures, were due to the suggestibility of his, mostly female, patients (for further detail see Finger, 2006). This devastating report destroyed Mesmer’s credibility and he soon left Paris to die in obscurity in Switzerland in 1815.

ELECTRICITY, MEDICINE, AND THE NERVE FORCE Mesmer’s career shows, if nothing else, the confusion that reigned in the latter part of the 18th century concerning the nature of electricity and magnetism. Many attempts were made by physicians more orthodox than Mesmer to use electricity for medical purposes. In America, Benjamin Franklin tried the effect of Leyden jar discharges on patients suffering a wide variety of complaints (see Finger, 2006). In England, John Wesley, Erasmus Darwin and Joseph Priestley interested themselves in the application of electricity to medicine. Priestley reviews a large number of such attempts in his 1775 volume, The History and Present State of Electricity, but concludes that they have in general proved unsuccessful (p. 377) and remarks that “no other part of the whole compass of philosophy affords so fine a scene of ingenious speculation” (Priestley, 1775, p. 411). In France Abbe´ Jean-Antoine Nollet, and in England Stephen Gray, astounded lay audiences by safely electrifying boys and girls. Enlightenment was slow in coming, but come it did. In America perhaps the greatest electrician of them all,

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Benjamin Franklin, not only drew electricity from the storm clouds but also simplified theoretical understanding by proposing that there was only one type of electricity, where formerly it had been thought there were two: vitreous and resinous. Finally, and most importantly for us, significant lines of research on electric fish and then amphibia began to bear fruit. That electric fish generated painful shocks had been known since antiquity, and the electric catfish can be found on Egyptian tomb paintings. The Nile was fished in early Egypt. In the middle of the 18th century Michel Adanson suggested that their electric organs were analogs of the Leyden jar (Adanson, 1759). As the 18th century wore on, electric organs were closely studied by Walsh, Cavendish and John Hunter. Indeed Hunter’s dissection of the electric organ of Torpedo (Fig. 9.3) provided a model from which, in 1799, J.W. Nicholson designed an “artificial torpedo” and this, in turn, influenced Volta’s work in constructing the first battery (Pancaldi, 1990). Marco Piccolino quotes with approval Wu’s (1984) comment that modern electrophysiology was born at the moment when Walsh first drew a spark from the shock of an electric eel (Piccolino, 2007). But if electrophysiology were born with electric eels, its long and difficult gestation took place with amphibia in Bologna. Luigi Galvani (1737–1798) was far from the first to use frog gastrocnemius-sciatic preparations. We saw above that Jan Swammerdam had pioneered this preparation 150 years earlier and in 1752 Leopoldo Caldani (1725–1813), Professor of Medicine at Bologna, used an “electrified rod” to stimulate the crural (or sciatic) nerves of frogs (see Brazier, 1984, p. 138). But Galvani lived at a time when the major lineaments of electricity and, in particular, bioelectricity were becoming clear. Moreover, he followed up his observations and experiments relentlessly and his interpretations received widespread attention. Galvani’s first (serendipitous) observations had been made in the early 1780s while dissecting a frog with a

Fig. 9.3. John Hunter’s dissections of Torpedo. (i) Under surface of female, (ii) upper surface of female, (iii) under surface of male. From Phil Trans Roy Soc 63: 461–480.

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metal scalpel close to an electrical machine. But he later observed contractions of frogs exposed on the railings around his house during thunderstorms and connected this with Franklin’s work. Further, he also observed contractions when the sky was cloudless. He did not then recognise that the latter contractions were due to stimulation arising from the two dissimilar metals with which his preparations were in contact. Galvani firmly believed that he was observing the actions of an internal “animal electricity.” Indeed he believed he had proved this by showing that contractions occurred when the sciatic nerve of one preparation was laid over the cut muscle of another. What we nowadays call “injury currents” were then unknown. He concluded that frog convulsions were caused by the transport of an electrical fluid from the nerves to the muscles. He believed that this fluid, similar to, but not identical with, inorganic electricity, was present in animal neuromuscular systems and was discharged into the muscles. His model was the Leyden jar. Galvani’s experiments became very well known during the 1790s, and not only by the scientific community. Indeed Barnadino Ferrari, in a letter from Milan in 1792, writes that “Now here the experiments are also repeated in the salons of ladies, and they furnish a very good spectacle for all.” But the interpretation of these experiments sparked much controversy. Had Galvani discovered an animal electricity that, although confined to the neuromuscular system, was in other respects identical to the “inorganic” electricity investigated by electricians such as Priestley? On the other hand, was Galvani’s electrical fluid in some way different from that studied by the electricians? Or, finally, was Volta right when he concluded that the results obtained by Galvani were not the consequence of an electric fluid confined to the nervous system at all, but due to stimulation of the tissue by two dissimilar metals? In the early 1790s Richard Fowler, a pupil of Monro Secundus at Edinburgh, repeated Galvani’s experiments and concluded that Volta’s interpretation was correct (Fowler, 1793). The effect was caused by the application of two dissimilar metals, in his case zinc and silver. Fowler’s account makes fascinating reading. It details an immense number of experiments on frogs and shows how puzzling electricity and animal electricity was to an acute 18th-century mind. It also shows, once again, the tenacity of the old neurophysiology. He writes of his great surprise at finding that contractility persisted even when the heart had ceased beating. He could hardly credit his eyes, he writes, yet it is so, and he does not expect to be believed. The old idea of the brain filtering an animating principle from the blood and transmitting it along the nerves was once again disproved, for how could this happen if

the heart had ceased beating? This idea, lingering from a bygone age, can also be found in Galvani’s De Viribus, where he writes that the electric fluid is produced by the activity of the cerebrum where it is in all probability extracted from the blood . . . The brain was, for the most part, still largely seen as a gland. Erasmus Darwin, at the very end of the 18th century, still believed that the brain had this filtering function: an idea which was common at Edinburgh in his student days. William Cullen, Professor of Medicine at Edinburgh at this time, held this view and as late as 1835 we find Baillarger drawing attention to the stratification of the cerebral cortex and observing that the analogy between the structure of the cerebral surface and the appearance of a galvanic apparatus suggests that it secretes an “electric fluid” into the underlying white matter. (Baillarger, 1835) For Erasmus Darwin, as for many others, this electric fluid had a psychological as well as a physiological side. It was not identical to that which Franklin had coaxed out of the thunder cloud or that which Pieter van Musschenbroek and Edwald Kleist had extracted from their coated jars. But how this animal electricity could show both psychical and physical attributes is nowhere made clear. Darwin is, once more, at one with his mid-century Edinburgh teachers. Both William Cullen and Robert Whytt agreed that, while it was an indisputable fact that an animating spirit interacted with the physical body, how this happened remained, and was likely to continue remaining, a mystery (Whytt, 1763, pp. 147–148; Cullen, 1827, p. 18).

LOOKING BACK The 18th century was indeed an age of transition. The time-honored neuropsychology of classical and medieval times, mechanized in Descartes’ L’Homme (1664), was undermined by microscopical observations and careful experimentation. Yet, until the very end of the century, when work on electric fish and amphibians began to suggest an acceptable successor to “animal spirit,” the old understanding of Man’s constitution held firm. Nevertheless, and paradoxically for a century that emphasized careful measurement and mathematical reasoning, the mechanistic iatrophysics of the early part of the century was everywhere in retreat, replaced by more mysterious forces called variously élan vital, vis viva, vis insita, animation, etc. Erasmus Darwin was not the only one to pour scorn on Descartes’ hydraulically driven “earthen machines” (Descartes, 1664, p. 1). The Cartesians forgot, as he

UNDERSTANDING THE NERVOUS SYSTEM IN THE 18TH CENTURY says, that so far as a living organism is concerned, “animation [is] its essential characteristic” (Darwin, 1794, vol. 1, p. 1). Perhaps one can see this turning away from iatrophysics toward something “far more deeply interfused” as part and parcel of the Romantic reaction to the seeming superficialities of the Enlightenment rationalism with which the century began. However this may be, the increased emphasis on nerves as the substrata of sensitivity and sensibility worked through to influence medical practice. Thomas Trotter, writing at the very beginning of the 19th century, observed that the last century has been remarkable for the increase in a class of diseases which had but little engaged the study of physicians before that period . . . nervous disorders. (Trotter, 1807) Perhaps we can see in this refocusing of medical attention the first glimmerings of that interest in “mental health” which, in the next century, led to the development of psychiatry and psychotherapy (see Collie, 1988). But it was not until the structure and the functioning of the neuromuscular system was better understood, and this awaited the second half of the 19th century and even more the 20th, that physicians could hope to develop successful treatments. These centuries and these treatments form the subject of later chapters in this volume.

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