Part 22

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.

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.

(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.)

(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.

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.