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Rh control the calibre of the arteries. The question of priority between him and Brown Sequard need not be considered here. His first account of his work was communicated to the Société de Biologie in December 1851. The following account of it is from his Leçons de physiologie opératoire (1879):—

“Let me remind you how I was led to discover the vaso-motor nerves. Starting from the clinical observation, made long ago, that in paralysed limbs you find at one time an increase of cold and at another an increase of heat, I thought that this contradiction might be explained by supposing that, side by side with the general action of the nervous system, the sympathetic nerve might have the function of presiding over the production of heat; that is to say, that in the case where the paralysed limb was chilled, I supposed the sympathetic nerve to be paralysed, as well as the motor nerves; while in the paralysed limbs that were not chilled the sympathetic nerve had retained its function, the systematic nerves alone having been attacked. This was a theory, that is to say, an idea, leading me to make experiments; and for these experiments I must find a sympathetic nerve-trunk of sufficient size, going to some organ that was easy to observe; and must divide the trunk to see what would happen to the heat-supply of the organ. You know that the rabbit's ear, and the cervical sympathetic of this animal, offered us the required conditions. So I divided this nerve; and, at once, the experiment gave the lie direct to my theory—Je coupai donc ce filet et aussitôt l'expérience donna à mon hypothèse le plus éclatant démenti. I had thought that the section of the nerve would suppress the function of nutrition, of calorification, over which the sympathetic system had been supposed to preside, and would cause the hollow of the ear to become chilled; and here was just the opposite, a very warm ear, with great dilatation of its vessels.” The experiments of Budge and Waller (1853) and of Schiff (1856) threw light on the action of these vaso-motor nerves, and on the place of the vaso-motor centre in the cord; and in 1858 Claude Bernard, by his experiments on the chorda tympani and the submaxillary gland, demonstrated their twofold influence, either to dilate or to constrict the vessels. “It is almost impossible to exaggerate the importance of these labours of Bernard on the vaso-motor nerves, since it is almost impossible to exaggerate the influence which our knowledge of the vaso-motor system, springing as it does from Bernard's researches as from its fount and origin, has exerted, is exerting, and in widening measure will continue to exert, on all our physiological and pathological conceptions, on medical practice, and on the conduct of human life. There is hardly a physiological discussion of any width in which we do not sooner or later come on vaso-motor questions.” (Foster, Life of Claude Bernard).

E. Cerebral Localization.—The study of the motor and sensory centres of the cerebral hemispheres began in clinical observation. Observation of cases, and examination of the brain after death (Bouillard, 1825, Dax, 1836, Broca, 1861), led men to believe that a particular area of the left frontal lobe of the brain did indeed govern and permit the use of speech. Physiological experiments had nothing to do with the discovery of the speech centres. “Bouillard in 1825 collected a series of cases to show that the faculty of speech resided in the frontal lobes. In 1861 his views were brought by Aubertin before the notice of the Anthropological Society of Paris. Broca, who was present at the meeting, had a patient under his care who had been aphasic for twenty-one years, and who was in an almost moribund state. The autopsy proved of great interest, as it was found that the lesion was confined to the left side of the brain, and to what we now call the third frontal convolution. … In a subsequent series of fifteen typical cases examined, it was found that the lesion had destroyed, among other parts, the posterior part of the third frontal in fourteen” (Hamilton, Text-Book of Pathology). From this clinical fact, that the movements of speech depend on the integrity of a special area of the brain's surface, and from the facts of “Jacksonian epilepsy,” and similar observations in medicine and surgery, began the experimental work of cerebral localization, by Hitzig, Goltz, Schiff, Ferrier, Yeo, Horsley, Beevor and many more. It would be hard to find a more striking instance of the familiar truth that science and practice work hand in hand.

Again, the experimental method has thrown a flood of light on the minute anatomy of the central nervous system. For example, we have what is called Marchi's method; it was described to the Royal Commission (1906-8) by Dr Head and Sir Victor Horsley. It was found, by Professor Waller, that nerve-fibres, separated from the nerve-cells which nourish them, degenerate in a definite way. The application of this law experimentally has been of great value. “Let me,” says Dr Head, “just take a simile. Imagine a wall covered with creepers arising from several stems. If we wished to know from which of these stems any one branch takes its origin, we could cut one stem, and every leaf arising from it would die, marking out among the healthy foliage the offshoots of the divided stem. This is the principle that has been used in tracing the paths in the nervous system. Gowers, by applying this method, discovered the ascending tracts in the lateral columns of the spinal cord.” If a microscopic section of a spinal cord, containing some fibres thus degenerate, be treated with osmic acid (Marchi's method), the degenerate fibres show dark: and in this way their course may be traced at all levels of the cord.

Indeed, it may truly be said that, alike in anatomy and in physiology, the whole present knowledge of the brain, the spinal cord and the nerves, is in great measure due to the use of experiments on animals. And this knowledge is daily applied to the diagnosis and treatment of diseases and injuries of the central nervous system. “In the case of operations on the brain, you have to form your opinion as to what is going on entirely from your knowledge of the physiology of the brain, and that we owe, of course, in the greatest measure to the discoveries of Hitzig and Fritsch and Ferrier.” That has all happened since 1870; and we are now able to cure epilepsy, we are able to cure abscess of the brain, and we are able to cure tumours of the brain. Then, in operations on the spinal cord, the same thing prevails. In fact, the first operation on the spinal cord I am responsible for, so that I know the history of the subject. The technique of that operation I owe entirely to experiments on animals. As regards operations on the peripheral nerves. Bell's operative treatment of neuralgia was guided entirely by his experiments on animals. Then we come to the great subject of nerve suture. The initial work bearing upon that subject was carried out by Flourens, who was the first, to my knowledge, to make experiments on animals, to suture nerves together, to investigate their function” (Sir Victor Horsley, evidence before the Royal Commission, vol. iv. p . 124).

[These notes cover a part only of the results that have been obtained in physiology by the help of experiments on animals. The work of Boyle, Hunter, Lavoisier, Despretz, Regnault and Haldane, on animal heat and on respiration; of Petit, Dupuy, Breschet and Reid, on the sympathetic system; of Galvani, Volta, Haller, du Bois-Reymond and Pflüger, on muscular contraction—all these subjects have been left out, and many more. In his evidence before the Royal Commission (1875), Mr Darwin said: “I am fully convinced that physiology can progress only by the aid of experiments on living animals. I cannot think of any one step which has been made in physiology without that aid.”]

1. Inflammation.—Pathology is so intimately associated with the work of the microscope that it is a new study, in comparison with physiology. In 1850 the microscope was not in general use as it is now; nor did men have the lenses, microtomes and staining fluids that are essential to modern histology. Bacteriology, again, is even younger than pathology. In 1875 it had hardly begun to exist. For example, in the evidence before the Royal Commission (1875) one of the witnesses said that they “believed they were beginning to get an idea of the nature of tubercle.” Anthrax was the first disease studied by the methods of bacteriology; and in his evidence concerning this disease, Sir John Simon speaks of bacteriology as of a discovery wholly new and unexplored. Then, in 1881, came Koch's discovery of the bacillus of tubercle. But a great advance was made, in days before 1875, by the more general use of the microscope. Every change in the tissues during inflammation—the slowing of the blood stream in the capillary vessels, the escape of the leukocytes through their walls into the surrounding tissues, the stagnation of the blood in the affected part—all these were observed in such transparent structures as the web or the mesentery of the frog, the bat's wing, or the tadpole's tail, irritated by a drop of acid, or a crystal of salt, or a scratch with a needle. It was in the course of observations of this kind that Wharton Jones observed the rhythmical contraction of veins, and Waller and Cohnheim observed the escape of the leukocytes, diapedesis, through the walls of the capillaries. From these simple experiments under the microscope arose all our present knowledge of the minute processes of inflammation. Later came the work of Melschnikoff and others, showing the importance of diapedesis in relation to the presence of bacteria in the tissues.

2. Suppuration and Wound-Infection.—Practically every case of suppuration, wound-infection or “blood-poisoning,” all abscesses, boils, carbuncles, and all cases of puerperal fever, septicaemia, or pyaemia, are due to infection, either from without or from within the body, by various forms of micro-organisms. The same is true of every case of erysipelas, or cellulitis, or acute gangrene—in short, of the whole multitude of “septic” diseases. The work done on these micro-cocci, and on other pathogenic micro-organisms, involved the study of the phases, antagonisms and preferences of each kind, their range of variation and of virulence, their products, and the influences on them of air, light, heat and chemical agents. The beginning of Lister's work was in Pasteur's study of the souring of milk, about 1856. Pasteur's discovery, that lactic fermentation was due to a special micro-organism, opened the way for modern surgery. Lister had been long studying the chemical changes in decomposing blood and other animal fluids; now he brought these studies into line with Pasteur's work. Thus, in 1867, in his first published writing on the antiseptic treatment of compound fractures, he speaks as follows: “We find that a flood of light has been thrown upon this most important subject by the philosophic writing of M. Pasteur, who has demonstrated, by thoroughly convincing evidence, that it is not to its oxygen, or to any of its gaseous constituents, that the air owes this property (of producing decomposition), but to minute particles suspended in it, which are the germs of various low forms of life long since revealed by the microscope, and regarded