Chapter X: Epilogue: 351 (4)

In spite of all his powers, however, Fabricius never shook himself free from ancient views, and especially he was steeped in the theories of Aristotle and Galen. This backward-looking habit prevented his work from being as important as it might otherwise have been. In connection with the circulation, for instance, he made a striking discovery, but wholly failed to draw out its most important lesson.

FIG. 42. DISSECTION OF A VEIN in the thigh and leg from a work _On the Valves of the Veins_, published by Fabricius in 1603 at Padua. These valves prevent the passage of the blood in any direction except toward the heart. They may be seen at the points P, Q, R, S, and T.

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In 1600 he published his book, _On the Valves of the Veins_. In it he says that these structures are so placed that their mouths are always directed _toward_ the heart (Fig. 42), yet he never gets an inkling that the effect of these valves must be to prevent blood flowing into the veins except toward the heart. He is too set on the old Galenic physiology to permit such a revolutionary thought. The real importance of Fabricius is, therefore, not so much as an investigator but rather as a teacher, a capacity in which he shone above all other physiologists for generations to come. He would deserve our remembrance if only as the master of the discoverer of the circulation of the blood, William Harvey.

The Englishman, William Harvey (1578-1657), after education at Cambridge, went to Padua in 1599, when Fabricius was at the height of his powers. Returning to England in 1602, he set up in practice in London. During the years which followed, he was dissecting and experimenting very industriously, and by 1615 had reached a clear conception of the circulation of the blood (Fig. 43), though he did not publish his discovery till some thirteen years later.

To discuss the actual steps by which Harvey made his discovery would be beyond our scope. He had, however, been well trained in experimenting on living animals by Fabricius, and had read widely in anatomical literature. He was of a contemplative turn of mind and his quiet and cautious temper, united with his enthusiasm and skill as an experimenter, provided a superb mental equipment for a life of scientific investigation.

Harvey, early in his work, reached two fundamental conceptions concerning the vascular system. He perceived that the valves in the veins would permit the blood to pass only towards the heart (Fig. 43), while those in the great arteries arising from the heart would permit the blood to pass only away from the heart. In connection with the movement of the blood, Harvey’s crucial point is that it must be _continuous_, and _always in one direction_. This really clinches the matter, for consider the capacity of the heart. Let us suppose that either ventricle holds but 2 ounces of blood. The pulse beats 72 times a minute and 72 × 60 times an hour. In the course of one hour, therefore, the left ventricle will throw into the aorta, or the right ventricle into the pulmonary artery, no less than 72 × 60 × 2 = 8,640 ounces = 38 stones 8 lb. In other words, in one hour the ventricle will throw into the great artery more than three times the body weight of a heavy man. Where can all this blood come from? Whither can it all go? It cannot come from the ingested food and drink, for no one could consume so much in one hour! It cannot reach and remain in the tissues, for they would soon all burst and ooze with blood! The solution of the puzzle, Harvey came to see, is that it is the same blood that is always being pumped into the arteries, and the same blood that is always coming back through the veins. In other words the blood _circulates_, a fact which Harvey proceeded to demonstrate with convincing thoroughness (Fig. 43).

FIG. 43. DIAGRAM TO ILLUSTRATE THE NATURE OF THE CIRCULATION OF THE BLOOD. Leaving the _left ventricle_, when the walls of that cavity contract, the blood is forced through the valves into the great artery known as the _aorta_. From the aorta it passes into smaller and ever smaller arteries, finally reaching the _systemic capillaries_ or the _portal capillaries_. After travelling through one or other capillary network it enters a vein. Thence it passes into larger and ever larger veins, until it ultimately enters the great vein known as the _vena cava_ that opens into the _right auricle_. It has now completed the Greater Circulation. As the right auricle contracts the blood passes through the valves between the right auricle and right ventricle into the _right ventricle_. From there it enters the Lesser Circulation, passing into the great _pulmonary artery_, which conducts it to the lung. In the lung the pulmonary artery breaks up into branches and finally into capillaries. Through these the blood travels until it reaches a tributary of the _pulmonary vein_ and finally the pulmonary vein itself. The pulmonary vein empties its blood into the _left auricle_. From the left auricle the blood passes at last into the left ventricle from which it started, having traversed both the Greater and the Lesser Circulations.

To understand the change which Harvey wrought in the conception of the workings of the body, this description and diagram should be compared with the description and diagram on pages 56-59.

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We may note that, though Harvey demonstrated the existence of the circulation, he was never able to follow it throughout, for he did not see the capillary vessels by which the blood is conveyed from the terminal branches of the arteries to the smallest tributaries of the veins. These were first demonstrated by Malpighi (p. 116).

The knowledge of the circulation of the blood has been the basis of the whole of modern Physiology and with it of the whole of modern rational Medicine. The attitude of Galen and Aristotle towards the heart and the great vessels passed into the shadow. The blood, it was seen, is a carrier always going round and round on the same beat. What it carries, and why, how and where it takes up its loads, and how, where, and why it parts with them, these are questions the answering of which has been the main task of Physiology in the centuries that have followed. As each of the questions has obtained a more and more rational answer, so clinical Medicine has always made a step forward, and has come to approach more nearly to a true science. Thus it is that the work of Harvey lies at the back of almost every important medical advance.

FIG. 44. THE VALVES in the superficial veins as seen in the bandaged arms of living men, from William Harvey’s great work on the _Circulation of the Blood_, printed in 1628. The bandage is seen on the upper arm in each case, and the valves are indicated, as in life, by nodes or swellings in the veins. If a finger is pressed along the vein from one valve to another as from node O to node H in a direction away from the heart, the vein from O to H will be emptied of blood. It will remain empty, since the valve at O does not permit the passage of blood away from the heart, but only towards it. This observation was Harvey’s starting point for his great discovery.

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§ 6. _Microscopic Analysis of the Animal Body._

The compound microscope was first made into an effective instrument by Galileo. It was, as it were, a _by-product_ of his invention of the telescope. With that instrument he had seen enough to convince himself that the movement of the Sun round the Earth was but an appearance. At the very time that Harvey was giving his first course of lectures securely in London, Galileo’s teaching was attracting the unwelcome attention of the Inquisition in Rome.

Galileo’s microscopes, however, were far less satisfactory than his telescopes. For optical reasons which we need not discuss, these early compound microscopes failed to give a clear picture. With any high degree of magnification, the image was always blurred and distorted. More than three centuries were to pass before a better compound system was introduced. But about 1650 a way was found of constructing and mounting simple lenses of very high power. Many of the most important microscopical discoveries of the second half of the seventeenth century were, therefore, made with a simple lens. This was notably the case with much of the work of the great investigators Malpighi and Leeuwenhoek (Fig. 49 A).

FIG. 45. LUNGS OF FROG, showing the capillary vessels from a figure by Malpighi in the rare first edition of his work _On the Lungs_, published at Bologna in 1661. A is the part of the larynx, B is the opening of the larynx into the trachea or air-tube leading to the lung. The letters EEE represent the outer surface of the lung and exhibit the network of capillary vessels. On the other side the sack-like lung has been laid open, and is viewed from the inside. The letters HHH are placed upon veins on the inner surface of the lung. These arise from capillaries which are indicated between the veins.

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Marcello Malpighi (1628-94) was born in the year in which Harvey’s work was published. He became a professor at Bologna, having early developed great skill in minute investigation. His first work, which appeared in 1661, supplied the element missing in the investigations of Harvey, for he describes the actual passage of blood from the arteries to the veins through the ‘capillary’ blood-vessels (Fig. 45). Harvey, who did not use a microscope, knew nothing of the capillaries. The object which yielded up the secret was the lung of the frog. This organ in the frog happens to be almost transparent, is very simple in structure, and is furnished on its surface with particularly conspicuous capillary vessels. Malpighi could hardly have selected an object better suited for this particular research. This important discovery of his drew the attention of scientific men in England. The Royal Society soon entered into correspondence with him, and during the remainder of his life undertook the publication of his researches.

FIG. 46 is the whole embryonic area, at about the end of the second day of incubation. The embryo itself is seen with its large head containing the three ‘cerebral vesicles’ (which are the rudiments of the brain), the large eye, the protuberant coiled heart (NM), from which vessels pass to the ‘vascular area’. The segmented vertebral column is well seen, as well as the vessels forming a network as they meander over the vascular area.

FIG. 47 exhibits the embryo more enlarged and in greater detail.

FIG. 48 is an enlarged figure of the heart; the part D will ultimately form the ventricle, B the auricle, and A the vena cava. At F the aorta sends forth three branches which unite again. The nature of these branches was not understood in Malpighi’s time. They have been explained in modern times by embryologists working under the inspiration of evolutionary theory as having once furnished the blood-supply to the gills of a fish-like ancestor.

FIG. 49 is a part of the segmented vertebral column still more enlarged.

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FIG. 49A. ONE OF LEEUWENHOEK’S MICROSCOPES. To understand the figure turn the book at right angles to the line of print. The object to be examined--here the tail of a small eel--is placed in water in the test-tube B. This test-tube is held firmly by two springs in the frame A. The microscope itself is simply a flat metal plate D, into which is let a very minute lens, the setting of which is shown above the letter D (when the head of the eel is downwards). The lens is focused by means of a fine screw which moves the whole plate.

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The contributions of Malpighi to biological knowledge were very numerous and important. The study of early development, embryology as it is now called, was greatly extended by him. The later stages of embryological development had been investigated by Fabricius (p. 110) and some additions to the subject had been made by Harvey. Malpighi, applying his microscope to the earlier germ of the animal body, described in detail the development of the organs, notably of the heart and the nervous system (Figs. 46-49). He also demonstrated the minute structure of the skin, spleen and liver, in all of which there are anatomical structures that still bear his name. He investigated microscopically the structure and physiology of insects and plants, and his figures of the cell-walls of the latter are good and clear.

FIG. 50. Oval blood corpuscles of salmon showing nuclei.

FIG. 51. Human red blood corpuscles.

FIG. 52. Drawing of human red blood corpuscles for comparison with Leeuwenhoek’s figures.

FIG. 53. Capillary network in web of frog’s foot. A, C and E are arterioles, B, D and F are venules.

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A most remarkable contemporary microscopist was the Dutchman, Anthony van Leeuwenhoek (1632-1723). Without medical or scientific training, desultory and secretive in his mode of working, he was withal an observer of genius and a very shrewd investigator. During his long and industrious life he made a series of disconnected discoveries which for originality and importance have been surpassed by no other microscopic observer. He improved and extended the knowledge of the capillary circulation of which Malpighi was the discoverer (Fig. 53), he gave figures of the blood corpuscles (Figs. 50-1), of spermatozoa and of fibres of muscles (Figs. 55-56a), and advanced the knowledge of embryology. He always worked with a simple microscope, using lenses of exceedingly short focal length (Fig. 49A). It is astounding that, with such an instrument, he saw and figured bacteria as early as 1683 (Fig. 54).

FIG. 54. THE FIRST REPRESENTATION OF BACTERIA. They were figured by Leeuwenhoek in the _Philosophical Transactions of the Royal Society_ of London in 1683.

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FIG. 55 shows a muscle teased up into bundles of fibres, magnified.

FIG. 56 is a more magnified view of a bundle of fibres. The cut fibres are shown at the end.

FIG. 56A is a very highly magnified view of a single fibre showing very clearly the striations that are very characteristic of voluntary muscle.

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The short life of a second Dutch microscopist of the seventeenth century, Jan Jacobz Swammerdam (1637-80), was abbreviated yet further, as regards scientific achievement, by his insanity. In his brief working period he produced his _Bible of Nature_ which, alone of the scientific writings of his age, is still consulted by modern naturalists for the unique beauty and accuracy of its figures. He extended the knowledge of embryology and he made a series of physiological experiments which involved the very modern physiological device known as the ‘nerve-muscle preparation’. He is thus the founder of an important department of Physiology. Swammerdam showed that, during contraction, a muscle does not increase in bulk, and that therefore the nerve brings nothing to it in the way of the hypothetical ‘nervous fluid’ in which many then believed (Fig. 63). He applied the same reasoning to the heart (Figs. 57-60). Swammerdam was perhaps the first to see the blood corpuscles. Like several of his contemporaries and followers, he made injection preparations of much beauty and delicacy. His great work was not published till after his death. The copper plates that he had prepared for it were found and purchased by Boerhaave (p. 140), who produced them at his own expense.

These microscopists and several others in the seventeenth century did much to explore the minute structure of the animal body. Their revelations showed at once an unexpected complexity of all the parts, and an unexpected resemblance of some of those parts which appear diverse to the naked eye. Thus, the structure of the body came to be subjected to a process that we may call ‘microscopic analysis’. For long after the time of these classical microscopists no effective improvements were made in the microscope, and the progress of microscopic analysis lay almost dormant. With the improvements in the microscope of the nineteenth century, the method was taken up again with triumphant results.

FIG. 57 is the simplest form of what physiologists call a ‘nerve-muscle preparation’. It is merely a living muscle dissected away from the body, but with its nerve still attached. In the experiment the two tendons of the muscle are held by the two hands. An assistant pinches the nerve with forceps. The muscle thereon contracts and draws the two hands together.

FIG. 58 shows the muscle passed through a glass tube. Its two tendons are fastened by two pins. When the nerve is pinched the pins are drawn towards each other, and the muscle, in contracting, fills the middle of the tube.

FIG. 59 shows the nerve-muscle preparation enclosed within a tube. This tube has a narrow neck in which, at _e_, is a drop of water. The other end of the tube is closed by a cork. The nerve may be squeezed by pulling the thread _c c_, which passes through the cork and drags the nerve into a narrow wire loop.

FIG. 60 is a similar experiment with the heart, which contracts and expands spontaneously and needs no irritation.

The experiments 59 and 60 show that during ‘contraction’ no new substance passes into the muscle, since it does not then increase in size. This gives the death-blow to the conception of a ‘nervous fluid’ passing into the muscle to cause contraction by distending it.

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§ 7. _From Alchemy to Chemistry._

During the sixteenth and the first part of the seventeenth century the basic science of Mechanics had been placed on a firm footing by Galileo. Astronomy, with Galileo and Kepler, had made the great break with the past. Anatomy and Physiology had put on their modern dress. Chemical knowledge, however, remained peculiarly backward. Many advances, it is true, had been made in technical processes, but investigations designed to throw light on theory were mostly prosecuted by the band of dupes and charlatans who, since the Middle Ages, had been seeking the Philosopher’s Stone. The old theory of the four elements, earth, air, fire, and water (p. 34), formed an ill basis for experiment. Some philosophers, it is true, had put forward crude atomic theories, but they had little experimental evidence to adduce. Nevertheless even the alchemists had made some advance and had, for instance, perfected a system of weighing.

The great defect of the ancient view of matter was that it contained no definite conception of the nature of a _pure_ substance. Metals, for instance, were regarded, like other substances, as a mixture in certain proportions of the four elements of Aristotle (p. 34). Thus, the transmutation of one metal or one substance into another by distillation did not seem an absurdity, or even a task of special theoretical difficulty.

The main agent in changing the chemical outlook was Robert Boyle (1627-91). He was a member of a small association of scientific men, the _Invisible College_, which met first in London, then in Oxford, and finally in 1663 was incorporated by Royal Charter as the _Royal Society_. These men were satisfied that the only way to learn anything effective about Nature was by observation and experiment. From their discussions all purely speculative views were excluded. They agreed to meet together solely to compare experiences, to demonstrate experiments, and to draw immediate deductions. None of them was more active in these matters than Boyle.

The actual chemical and physical discoveries of Boyle were very numerous, but his great achievement, the real service he rendered to learning in general and to medicine in particular, was his introduction of a new spirit into Chemistry. Under him that study was no longer prosecuted for purely practical ends; it was set free from the mystic factor in Alchemy and it was loosed from the chains which bound it to Medicine, to the disadvantage of both. Chemistry thus became an independent science, the principles of which were to be ascertained by experiment, and its truths pursued for their own sake.

Boyle demonstrated that the air is a material substance and has weight. By means of his air-pump, he proved clearly that this substance is necessary for the support of respiration (Fig. 63). The law of the compressibility of gases is still known by his name. Most important of all Boyle’s contributions to chemical theory was his adumbration of the conception of a chemical element in our modern sense, and his view, which he borrowed from another philosopher, of the atomic structure of matter.

Under the inspiration of Boyle and his colleagues, chemical works of the second half of the seventeenth century exhibit in general a positive, cautious, experimental spirit, and show a great contrast to the mystical and obscure writings of the first half of the century, which have much affinity with Alchemy. A fine exponent of this new spirit was John Mayow (1645-79), who was prevented by an early death from fulfilling all his promise. He was the first to recognize clearly that there is a substance or principle in air which is concerned at once with combustion, respiration, and the conversion of venous into arterial blood. In this sense he was the discoverer of Oxygen (Figs. 74 and 75).

§ 8. _The Medical Theorists._

The great advances in the physical and biological sciences, instituted during the sixteenth and seventeenth century, left the old medical theories derelict. We have already traced the wrecking of the Galenic physiology. With its destruction, the old ideas concerning the three types of spirit, natural, vital, and animal, went by the board. The doctrine of the circulation of the blood (p. 113) and the investigations of the new Chemistry accorded ill with the old humoral pathology, which ascribed all disease to excess or defect of one of the four humors, blood, phlegm, bile, and melancholy (p. 34). Numerous fresh theories arose, of which the more important can be classed under the three headings _Iatrophysics_, _Iatrochemistry_, and _Vitalism_.

(_a_) _Iatrophysics._

The physical discoveries of Galileo and the demonstrations of Sanctorius (p. 108) and of Harvey (p. 111) gave a great impetus to the attempt to explain the workings of the animal body on purely mechanical grounds. The writers who took this point of view are known as the _Iatrophysicists_. One of the earliest and most impressive exponents of physiological theory along these lines was the French philosopher René Descartes (1596-1650). His work on the subject appeared posthumously in 1662. It is important as the first modern book entirely devoted to the subject of Physiology.

Descartes had not himself any extensive practical knowledge of the subject with which he was dealing. On theoretical grounds he set forth a very complicated apparatus which he believes to be a model of animal structure. Subsequent investigation failed to confirm his findings, and his work soon passed into oblivion. For a time, however, it attracted much attention and many followers. A strong point in his theory is the great stress laid upon the nervous system, and its power of co-ordinating the different bodily activities. Thus stated, his view may seem not far from the modern standpoint, though in fact he was grotesquely wrong in detail. An important part of his theory is the complete separation of Man from all the other animals. Man, according to him, differs from all other animals by his possession of a soul, which is situated in a structure in the brain known to physiologists as the ‘pineal body’! Animals, he held, have no soul, and all their actions and movements, even those which seem to express pain or fear, are purely automatic. It is the modern theory of ‘behaviorism’ with man excluded! (Figs. 62 and 63.)

FIG. 62. DESCARTES’ conception of the relation of a sensory impression and a motor impulse. The image of the object ABC passes to the eye and is formed on the retina. Owing to the optical properties of the eye, it is there inverted. The image is inverted yet again within the brain, where it passes to the pineal gland H at the point _b_. The position and character of the image formed on the retina determines the nature and distribution of its effect on the pineal body. According to the nature and distribution of that effect is the result on the nerve, and through it, by the passage of nervous fluid, on the muscles. The movement in the nerve is initiated at the point _c_. The relation between _b_ and _c_ is an insoluble mystery in which is wrapped up the very nature of the soul. (From the posthumous work of Descartes on Physiology.) ]

FIG. 63. DIAGRAM OF DESCARTES to illustrate his theory of nervous action. P R and _q s_ are nerves which supply the muscles of the eye T and V V. Descartes held that these nerves were hollow and provided with valves, which can be seen at the point at which the P R and _q s_ first branch. These valves were partly controlled by little fibrils (which can be seen in the main stems of P R and _q s_ and in certain of their branches). These valves control the movement of the fluid within the hollow spaces of the nerves. Additional complication is lent to the scheme by the fact that P R and _q s_ intercommunicate at certain points. The view of Descartes, and all such theories of nervous fluid, were destroyed by the experiment of Swammerdam (Figs. 57-60), which, however, long remained unpublished.

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More lasting was the achievement of Giovanni Alfonso Borelli (1608-79), an eminent mathematician who was professor at several Italian universities and the friend of Galileo and Malpighi. Stirred, like Descartes, by the success of Galileo in giving a mathematical expression to mechanical events, Borelli attempted to do the same with the animal body. In this undertaking he was, in fact, very successful. That department of Physiology which treats of muscular movement on mechanical principles was effectively founded and largely developed by him. Here his mathematical and physical training was specially useful. He endeavored, with some success, to extend mechanical principles to such movements as the flight of birds and the swimming of fish. When he came to an analysis of some of the other activities of the body, such as the action of the heart, or the movements of the intestines, he was less successful, and he naturally failed altogether in his attempt to introduce mechanical ideas in explanation of what we now know to be chemical processes, such as digestion in the stomach.

Undeterred by Borelli’s failure, other writers sought to find mechanical explanations of physical processes. As is usual in such cases, the amount of theory was inversely proportional to the amount of knowledge. The views of some of the later ‘Iatrophysicists’ became very fantastic. Belated representatives of the school are the writers of the great French _Encyclopédie_ (1751-72), and notably its main author, the man of letters, Denis Diderot (1713-84).

FIG. 64. DIAGRAMS FROM BORELLI, showing one of his attempts to analyse the movements of the muscles, in this case of the arm, according to the principles of the science of Mechanics as expounded by Galileo. The figure should be considered in conjunction with Fig. 65 opposite.

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(_b_) _Iatrochemistry._

Just as there were some who sought to explain all animal activity on a mechanical basis so others resorted to chemical interpretation. These may be termed _Iatrochemists_. The most prominent was Franciscus Sylvius (1614-72), professor of Medicine at Leyden. That university had become, in the second half of the seventeenth century, the most progressive scientific center north of the Alps. It was the seat of the first University laboratory, built at the instigation of Sylvius.

Sylvius devoted much attention to the study of salts. He recognized that they were the result of the union of acids and bases, and he attained to the idea of chemical affinity--an important advance. He looked at the phenomena of life also from the chemical point of view. Well abreast of the anatomical knowledge of his day, and accepting the broader lines of mechanistic advance in Biology, such as the circulation of the blood and the mechanics of muscular motion, Sylvius sought to interpret other activities in chemical terms. His position and abilities as a teacher gave his views wide currency and he and his pupils occupy a large part of the field of medical theory until well into the eighteenth century.

Under the influence of this school, almost all forms of vital activity were expressed in terms of ‘acid and alkali’ and of ‘fermentation’. The latter process was assumed to be of a chemical order, and no clear distinction was made between changes that are brought about by ‘unorganized’ ferments, such as gastric juice or rennet, and changes that are brought about by the action of micro-organisms, such as alcoholic fermentation or leavening by yeast. Nevertheless, the school of Sylvius and its immediate successors added considerably to our knowledge of physiological processes, notably by their examination of the body fluids, especially the digestive fluids such as the saliva, and the secretions of the stomach and of the pancreas.

FIG. 65. DIAGRAM OF MUSCULAR ACTION involved in lifting a weight in the hand. It illustrates how muscular movement may sometimes be resolved into terms of the lever. In practice, however, it is usually necessary to involve a whole system of levers, pulleys, resistances, &c., as Borelli clearly perceived. (Compare Fig. 64.)

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(_c_) _Vitalism._

Yet another school of medical theorists arose under the leadership of the German chemist and physician, George Ernest Stahl (1660-1734). Stahl is best remembered as the author of the famous theory of _phlogiston_, a hypothetical substance with which bodies were supposed to part during the process of burning (p. 151). He is important in the history of science for his success in grouping chemical phenomena and therefore in systematizing the study of the subject. For our purpose, however, Stahl stands as the protagonist of that view of the nature of the organism which now goes under the term _Vitalism_. Though expressed by him in obscure and mystical language, it is, in effect, a return to the Aristotelian position and a denial of the view of Descartes. To Descartes the animal body was a machine. To Stahl the word _machine_ expressed exactly what the animal body was not. The phenomena characteristic of the living body are, he considered, not governed by physical and chemical laws, but by laws of a wholly different kind. These laws are the laws of the _sensitive soul_. The _sensitive soul_ of Stahl is, in its ultimate analysis, not dissimilar to the _psyche_ of Aristotle (p. 32). Stahl held that the immediate instruments, the natural slaves of this sensitive soul, were chemical processes and his Physiology develops along lines of which Aristotle could know nothing. This does not, however, alter the fact of his hypothesis being an essentially vitalistic one of Aristotelian origin.

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The language and the theories of the Iatrophysicists, the Iatrochemists, and the Vitalists of the seventeenth and eighteenth centuries have long been discarded by men of science in the form in which they were originally propounded. Nevertheless, they represent three attitudes to the activities of living things which have present and current meaning. Each seems to present some aspect of truth. Whether some physiological thinker will combine all three aspects into one coherent whole, it is for the future to decide. Yet it is certain that all three lines of approach remain of value, and the stimulus provided by each of the three inspires investigation at the present day. In this sense we enter on the period of modern Medicine in the seventeenth century. In this sense the foundations of modern rational Medicine may be said to have been laid by Borelli, Sylvius and Stahl, with Galileo, Boyle and Harvey standing behind them.

V

THE PERIOD OF CONSOLIDATION

(FROM ABOUT 1700 TO ABOUT 1825)

§ 1. _The Reign of Law._

During the sixteenth and seventeenth centuries the human mind cast off its medieval vestments and, having refreshed itself at the spring of Antiquity, turned to array itself in the garments of the New Philosophy. The advent of new ideas and new knowledge had been very rapid. The _method_ of Research had been determined by Galileo at the beginning of the seventeenth century. The _meaning_ of Research was determined by a second great investigator, Newton, at the end of the same century.

The change wrought in the thought of their time by Vesalius, Galileo, Harvey and their like was quantitative rather than qualitative. They discovered new laws of Nature, but the discovery of such new laws was hardly unprecedented. Law had been traced in the heavens from of old. The rules of planetary and stellar motion had been gradually developed from the simple astronomical theories of the ancients. The great astronomers of the sixteenth and seventeenth centuries did not hesitate to appeal to the records and doctrines of medieval writers, for new mathematical relationships of the heavenly bodies had been elicited even during the Middle Ages. In the sixteenth century Astronomy under Tycho (died 1601) put her house in order for the ‘Great Instauration’ of the coming age. And then Galileo startled the world (1604) with that new star of his (p. 104), among the most remote heavenly bodies in the very region held by the Aristotelian and Platonic schemes to be utterly changeless. The Revolution in Thought had begun, though no new order had been established.

By 1618 Kepler had enunciated his ‘three laws of planetary motion’, bringing these movements into an intelligible relation with each other. Then the experimental philosophers set forth to establish terrestrial mechanics. They determined the mode of action of gravitation, and Galileo came near to the ‘three laws of motion’ which we call Newton’s. But it was Newton who first affirmed them clearly and succeeded in linking them with Kepler’s laws of planetary motion. Before Newton, no man had shown or perceived that rule by which the natural succession of earthly phenomena is in relation to that of the heavenly bodies. Nay, Faith and Reason alike would have been against such a view. To prove that the relationship amounted to identity, to move men’s minds to see that the force that causes the stone to fall is that which keeps the planets in their path, this was Newton’s unique achievement. It was Newton who first enunciated a law whose writ ran alike in the Heavens and on the Earth. With Newton the Universe acquired an independent rationality, and the whole cosmology of Aristotle, of Galen, and of the Middle Ages lay in the dust.

When Newton had completed his work, the Gravitation of the Earth and of the Heavens was seen to be one, and all the Mechanism of the Universe lay spread before him. The vision was set forth in his _Principia_ (1687). It established a view of the structure and working of the Universe which has survived to our own generation.

And now as to the change wrought in men’s minds. It was something more than a Revolution. It was the establishment of a New Order. Newton conceived a working Universe wholly independent of the Spiritual Order. As to how far his vision is philosophically tenable and as to how far he realized its nature, these are matters which we need not discuss here. There can, however, be no doubt that Newton utterly destroyed the very foundations of medieval thought. With Newton there sets in the last stage of ‘scientific determinism’.

During the two centuries and a half since the _Principia_ appeared, Science has developed prodigiously along the lines into which Newton led her. In reliance on the universality of Natural Law, the stars in their courses have been paced, weighed, measured, analysed. The same process, directed to our own planet, has traced its history, determined its composition, demonstrated its relation to other bodies. Physicist and chemist have suggested a structure in terrestrial matter similar to that of the stars and suns. The world has been reduced to a unitary system. Wherever men have sought Law, they have found Law. With search skilful enough and patient enough, Law has ever emerged. It has been _the Age of the Reign of Law_.

It is true that in our own time philosophers in general have come to see that these Laws of Nature are within us as much as without; that they are, in part at least, the result of the structure of our minds. This is a point of view, however, which has not affected, and perhaps will not affect, the working man of science. His constant occupation, since the days of Newton, has been the pursuit of Law, and he has always been satisfied that Law has only to be sought in order to be found. This conception has affected the medical and biological sciences very deeply. Thus the influence of the Newtonian philosophy is as traceable in them as it is in the astronomical and physical sciences. Galileo showed men of science that weighing and measuring are worth while. Newton convinced a large proportion of them that weighing and measuring are the _only_ investigations that are worth while. The question as to whether this view is ultimately true or philosophically justifiable does not need discussion at the moment. The point, for our immediate purpose, is that the view has been and is very widely held.

§ 2. _The Rise of Clinical Teaching._

The eighteenth century dawned with the refreshing breeze of Newtonian philosophy blowing through it. During the previous two hundred years there had been an immense amount of new and fruitful research along diverse lines. Chemistry and Mechanics, Botany and Comparative Anatomy, Descriptive Anatomy and Experimental Physiology, Epidemiology and Microscopic Analysis, all had yielded startling results. The new generation was bewildered with the very mass and novelty of the material. The Biologists of the time must have been well nigh hopeless of reducing their vast accumulations to order, when they contemplated the beauty and symmetry of the mathematical relations that Newton and his followers had introduced into Cosmic conceptions. Thus the eighteenth century is a period for Biology of pause and consolidation during which attempts were made to introduce unitary conceptions into the mass of accumulated material. It was, moreover, a period of consolidation not only of ideas but also of teaching. These tasks at first turned men’s minds away from the immediate accumulation of further knowledge. So it is that the first half of the eighteenth century exhibits something of a gap in the progress of Research. The medical field is largely filled by two great figures, Boerhaave and Haller.

Until the seventeenth century there was no systematic clinical teaching. The Universities gave medical degrees on the basis of a spoken disputation. No contact with the patient was demanded. The first effective attempt to change this was at Leyden, where about 1636 clinical teaching was instituted. Owing to this, and to the fact that, as at Padua, students of every religious denomination were accepted, Leyden became much frequented by foreign and especially by Protestant students. The attractions of the place were increased by Sylvius (pp. 131-2) who, in the second half of the seventeenth century, added laboratory instruction to his clinical teaching. Leyden had several eminent anatomists, while its botanic garden and museums added to the practical character of the medical instruction that it offered.

Hermann Boerhaave (1668-1738) was first appointed as a teacher at Leyden in 1701. At once the medical school attained a front rank reputation which rapidly came to surpass even that of Padua. Boerhaave had very few beds at his disposal, but never did man make better use of his opportunities. Besides clinical, chemical, botanical and anatomical instruction he followed such of his patients as died into the post-mortem room and there demonstrated to his students the relation of lesions to symptoms. He is thus the introducer of the method of medical instruction still in vogue in our modern medical schools.

Boerhaave was a man of wide culture. He rescued and published the plates of the priceless _Bible of Nature_ of Swammerdam (p. 121). He brought to Leyden the best anatomist of his age, Bernard Siegfried Albinus (1697-1770). With him Boerhaave edited in superb form the collected works of Vesalius (1725, p. 85 ff.). The edition exhibits remarkable prevision of the scientific needs of the scholarship of our own time. To Albinus, and indirectly to Boerhaave, we owe the most beautiful of all works on muscular anatomy (1747), a book still in current use (Fig. 66). Apart from his clinical ability and acumen Boerhaave was a skilled chemist, botanist, and anatomist.

With all these accomplishments Boerhaave was better able than any man of his time to achieve something like a medical synthesis, to bring all the sciences to the service of the patient. Taking one thing with another, considering his influence as a teacher, his clinical acumen, his power of inspiring younger workers, his wide learning, his balanced vision, his eagerness for new knowledge, his sanity, his humanity, his generosity, and his prophetic power, Boerhaave must be regarded as the greatest physician of modern times. To him the debt of British Medicine, and through it of British well-being, is quite incalculable. Through his pupils he is the real founder of the Edinburgh Medical School, and through it of the best medical teaching in the English-speaking countries of the world. The success of the Edinburgh school, founded while the great Leyden professor was still in his prime, can be ascribed to two causes which are perhaps reducible to one--the inspiration of Boerhaave. These two causes are, firstly, the enthusiasm of its early teachers, and, secondly, the concentration of all the medical teaching, both clinical and subsidiary, in one great university school.

§ 3. _Physiology passes to the Modern Stage._

The only figure in the eighteenth century whose influence is comparable to that of Boerhaave is his pupil, the Swiss Albrecht von Haller (1708-77), one of the most accomplished men of all time. In actual scientific achievement Haller stands, indeed, far above his master. He achieved distinction as poet, botanist, anatomist, and novelist, carried on a prodigious correspondence, was an exceedingly learned bibliographer, and perhaps the most voluminous of all scientific authors. His special distinction, however, is as a physiologist.

Haller’s great work, _Elements of the Physiology of the Human Body_ (1759-66), marks the modernization of the subject of which it treats. Of the highest importance were his researches on the Mechanics of Respiration, on the formation of bone, and on the development of the embryo. He did good work on the action of the digestive juices. His most important contributions, however, are his conceptions of the nature of living substance and of the action of the nervous system. These conceptions formed the main background of biological thinking for a hundred years, and are still integral parts of physiological doctrine.

All departments of Medicine must be influenced by the views we may hold on the nature and action of the nervous system, just as all parts of the body are influenced and indeed are linked together by that system. Thus the growth in knowledge of the physiology of the nervous system is extremely important to us if we would gain a true idea of the progress of Rational Medicine.

When we look into the history of nervous Physiology before Haller, we shall be struck by the smallness of the observational foundation of a vast speculative structure. That we may be the more charitable in our judgment of such fanciful developments, we may recall that the Mind is so constructed that it can take little interest in the accumulation of instances unless it can adduce general laws therefrom. Theory is thus as necessary to practice as practice to theory. The earlier doctrines of the nature of nervous action are, however, so unlike those we now hold that we can afford to pass over them lightly. They consist of speculations on the topic of the seat of the soul, together with explanations which suppose the passage either of a fluid or of some chemical change down the nerves. Haller was the first to construct a theory of the nervous system that has an appearance of modernity.

During the seventeenth century the favorite doctrine of nervous action supposed the existence of a nervous fluid. This, it was held, passed down the nerves to inflate or extend the muscle fibers. Inflation was supposed to shorten the fibers and so the muscle came to contract. An exquisite experiment by Swammerdam with his nerve-muscle preparation had disproved this (p. 123). But Swammerdam’s work was unknown till published by Boerhaave in 1736, and so the matter stood till Haller’s time.

Haller concentrated the problem on an investigation of the fibers. A muscle fiber, he pointed out, had in itself a tendency to shorten with any stimulus, and afterward to expand again to its normal length. This capacity for contraction Haller, following a predecessor, called _irritability_. He recognized the existence of ‘irritability’ as an element in the movement of the viscera, and notably of the heart, and of the intestines. The feature of ‘irritability’ is that a very slight stimulus produces a movement altogether out of proportion to itself, and that it would continue to do this repeatedly so long as the fiber remained alive.

But besides the force inherent in a muscle fiber Haller showed that there was another force which comes to it from without, is carried from the central nervous system by the nerves, and is the power by which muscles are normally called into action. This force, like that of irritability, is independent of the will, and like it can be called into action after the death of the animal. Haller thus distinguished the _inherent muscular force_ from the _nerve force_. Both these forces he further distinguished from the natural tendency to contraction and expansion, under changing conditions of humidity, pressure and so on, of all tissues, living or dead.

Haller, having dealt with the question of movement, turned to that of feeling. He was able to show that the tissues are not themselves capable of sensation, but that the nerves are the sole channels or instruments of this process. He showed how all the nerves are gathered together into the brain, and he believed that they tended to its central part. These views he supported by experiments and observations involving injuries or stimulation to the nerves and different parts of the brain. He ascribed special importance to the cortex, but the central parts of the brain he regarded as the essential seat of the living principle, the Soul.

Throughout his discussion Haller never falters in his display of the rational spirit. He develops no mystical or obscure themes, and, although his view of the nature of Soul may lack clarity, he separates such conceptions sharply from those which he is able to deduce from actual experience. He is essentially a modern physiological thinker, and certain of his themes were developed by workers who come on the frontiers of what we have called the ‘period of consolidation’.

Among these workers we would select the Scottish surgeon Sir Charles Bell (1774-1842), who in 1811 showed that of the two roots from the spinal cord by which all the nerves of the body arise one root conveys only sensory elements while the other conveys only motor elements (Fig. 98, p. 208). By this discovery Bell not only completed the views of Haller on the central nervous system, but also brought them within the range of practical Medicine.

§ 4. _Some Physiological Advances._

Haller provided a philosophical basis to physiological conceptions. There were, however, other workers of the time who added to the knowledge of actual workings of the animal body. First among these, both in time and eminence, stands the English country clergyman Stephen Hales.

The Rev. Stephen Hales (1677-1761) was by temper a biologist, but he had received a training in Mathematics and Physics. With this ideal equipment, he proceeded to investigate the Dynamics of the Circulation. His method consisted in applying the principle of the pressure gauge or manometer to living things. By tying tubes into the arteries and veins of animals, he was able to record and measure the blood-pressure. He thus laid the foundation of an important mode of studying the diagnosing disease. He extended his exact investigations into most of the mechanical aspects of the circulation. He computed the circulation rate and he estimated the actual velocity of the blood in veins, arteries, and capillary vessels. He made a very important contribution by showing that the capillary vessels are liable to constriction and dilatation, a knowledge that has since become not only important for physiological theory but of primary significance to the practising physician (p. 309). He began to explore the wonderful mechanism of the heart by which that organ adjusts itself to its needs of output. He exhibited his versatility by important contributions to many other departments, as, for instance, his discoveries on Respiration, his improvements in Ventilation (Fig. 67), and his campaign for Temperance. All his work is characterized by simplicity and directness, the supreme marks of his genius.

FIG. 67. WINDMILL VENTILATOR designed by the Rev. Stephen Hales, and erected by order of the Aldermen of the City of London, in 1752, on the roof of Dick Whittington’s Gate at Newgate Prison. From a print in the British Museum.

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In the meantime considerable progress was made in the knowledge of the digestive processes. The French naturalist, René Antoine de Réaumur (1683-1757), best remembered for his thermometer (1731) and for his superb work on insects (1734-42), made a series of experiments on gastric digestion in birds (1752). By an ingenious contrivance he succeeded in obtaining gastric juice in a pure state. He was able to demonstrate its power to dissolve food substances in a test-tube kept at body temperature. This was important, since many believed that the process of solution was the result of a churning process induced mechanically by the muscles of the stomach-wall. Réaumur thus gave the death-blow to the Iatrophysical conception of digestion (p. 130).

The investigation of gastric digestion was further pursued by a versatile Italian, the Abbé Lazaro Spallanzani (1729-99), who showed that the churning action is an aid, but not an essential, to the process of digestion (1782). He proved that digestion was not of the nature of putrefaction and differed essentially from the fermentation of wine. Spallanzani thus improved on the view of Sylvius (p. 132), and took a step towards that solution of the natures of putrefaction, fermentation, and digestion which was finally provided by Pasteur (p. 225). He showed that the gastric juice was secreted by the stomach itself, and not introduced into it from other organs. A suspicion that the gastric juice contained a free acid crossed his mind. He observed that it curdled milk and so began our knowledge of a separate ferment, that of ‘rennet’. Spallanzani’s results may be summarized by saying that he showed that gastric juice had a solvent power _sui generis_, and that this power or faculty was of a different order from putrefaction or vinous fermentation.

The phase of digestive physiology represented by Réaumur and Spallanzani was brought to a close by the English physician William Prout (1785-1850), who demonstrated in 1823 the existence of free Hydrochloric Acid in the stomach. He showed that the presence of this acid was necessary for gastric digestion, but that the actual process of solution of food was the work of another agent. The matter was at last brought into the range of medical practice by an American Army Surgeon, William Beaumont (1785-1853), who, in the ten years ending 1833, had the opportunity to investigate gastric juice in a man who, having been shot in the stomach, had a permanent fistula. Through this the juice could be obtained and the lining membrane of the stomach examined at will.

Experiments illustrating the effects of metallic contacts on the nerves and muscles of frogs’ legs. From A. Galvani, _On Electric Forces_, 1792.

FIG. 68. Contact is established between water in two dishes. In one lies the end of the nerve with the spinal cord and vertebral column attached. In the other are the feet of the frog.

FIG. 69 shows contact by a metal bar with two damp mats on one of which lies the spinal cord and on the other are the feet.

FIG. 70 shows a broken contact which can be completed by bringing the metal rods together.

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An important department of Physiology was opened by the extension of the knowledge of electric phenomena to the living body. Static electricity had been studied since the beginning of the seventeenth century. Luigi Galvani (1737-98) of Bologna, while investigating the susceptibility of nerves to irritation, showed that nervous action could be induced by electrical phenomena (1791). He was, as a matter of fact, producing an electrical current. Many thought at the time that a new kind of ‘animal electricity’ had been produced and they dubbed it ‘galvanism’.

Alessandro Volta (1745-1827) of Pavia, deviser of the ‘Voltaic pile’ (Figs. 71-3), had long been working at electricity. He was able to demonstrate (1800) that galvanism is without any essential animal relationship, and showed that a muscle can be thrown into continuous contraction by repeating electric stimulations.