Part 23

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.

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.

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.

Humbug and misunderstanding in connection with the electrical relations of living tissues were rife, and it was not till after the period we are now considering that electricity came to take a place in rational Medicine. The change came with E. Du Bois-Reymond (1818-96), who took the matter up scientifically about the middle of the nineteenth century (1843 onwards). He showed that a nervous impulse is accompanied by the passage along the nerve of a change of electrical potential. It should be added that, despite all the work since done upon the nervous system, this is still the only physical accompaniment of a nerve impulse that has been detected.