Laennec's work was so well done that it needs to-day little change in the way either of correction or addition. In the diagnosis of diseases of the heart his endeavors were soon supplemented by the investigations of his disciples of the Dublin School and other great leaders in clinical medicine.

After completing the second edition, which was almost a new work, of the "Mediate Auscultation," Laënnec once more retired to Finistère in the hope of again reëstablishing his health. The sea breezes and outdoor life failed, however, to revive his powers, exhausted by years of constant activity, and August 13, 1826, he succumbed to one of those diseases from which his genius has rescued so many victims.

REFERENCES

Camac, C. N. B.: Epoch-making Contributions to Medicine and Surgery. 1909.

Meunier, L.: Histoire de la Médecine. 1911.

Thayer, W. S.: "Laënnec One Hundred Years After," Canadian Medical Association Journal, vol. IX, no. 9, Sept., 1919.

Walsh, J. J.: Makers of Modern Medicine. Third edition, 1915.

CHAPTER XI

ADVANCES IN PHYSIOLOGY

AMONG the many advances in physiology in the nineteenth century must be mentioned above all the progress made in the study of the functions of the nervous system through the investigations of the experimental physiologists, Charles Bell, Magendie, Marshall Hall, Johannes Müller, and Claude Bernard. For this progress the way had been prepared by Albrecht von Haller. Born at Berne, Switzerland, October 16, 1708, Haller was favored by striking natural endowments, as well as by almost unlimited opportunities for education. The accounts of his linguistic, literary, and scientific attainments while he was still little more than a child are not far from incredible. His more advanced education began at Tübingen, where he studied anatomy and, under the direction of Camerarius, botany. From Tübingen he was drawn to Leyden by the reputation of Boerhaave. After graduating at the age of nineteen, he visited England, where he came in contact with some of the leading British scientists. At Paris he came under the influence of the anatomist Winslow, and, at Basel, before returning to his native city, he studied mathematics under Jean Bernouilli. In

1736 Haller, after years of private practice, of a limited sort, and much study, was induced by George II of England to accept a professorship of medicine, anatomy, botany, and surgery in the newly established university of Göttingen. Here as elsewhere he was indefatigable. After seventeen years' activity at this Hanoverian seat of learning he returned to his native Berne, where he spent the remaining twenty-four years of his life.

Of Haller's many claims to distinction his work as a physiologist is the most convincing, though his knowledge of human and animal structure, on which his knowledge of physiological function was based, was very thorough. Haller's influence increased the range of experiments on living animals. He declared that, in spite of its apparent cruelty, vivisection is of more value in the study of physiology than all other methods and that a single experiment of this kind has often cleared up misconceptions soluble by no other means of investigation. The function and structure of mammals, birds, fishes, and still lower forms of life, helped him to explain the anatomy and physiology of man.

Haller laid the progress of physiology under par ticular obligation by his experiments on muscles and nerves and by the doctrine he based on these experiments. In 1752 they were reported to the Royal Society of Göttingen, of which he was the founder

and president. He taught that irritability is the inherent property of muscle, while sensibility is the characteristic property of nerves. He used the term "irritability" in the sense of "contractility"; that is, in a much more restricted sense than Glisson, who in 1677 had spoken of the irritability of all animal tissues. Haller admitted that the usual stimulation which brings about the contraction of a muscle is conveyed by means of the nerves. Yet for this means of stimulation there might be substituted other forms which prove effective even when the connection between the nerve and the muscle is severed. It is the function of the nerves, on the other hand, to transmit to the consciousness the changes called forth by peripheral stimuli; or, in other words, the nerves are exclusively the organs of sensibility. For example, the retina is a network of nerve fibers which serve to transmit sensations of light. The rays of light coming from the object before us produce an impression on the retina which constitutes a stimulus of the optic nerve. What we feel is not the object itself, but the impression which the object makes on the particular nerve in question. It would seem to follow from this that the nerve of each sense has its own special mode of responding to stimulation, and that sensations are subjective in character, though they afford grounds for arriving at a judgment in reference to the nature of the outer

world. Irritability may be found in detached parts of the body quite withdrawn from the empire of the soul. It is therefore absurd to seek to identify the soul with mere irritability. The nerves, the true organs of sensibility, contain, Haller was inclined to believe, a subtle, automatic fluid, being influenced no doubt in this belief by the contemporary discoveries in electricity. He also taught that memory is developed through the persistence of impressions on the brain substance.

In 1811 Sir Charles Bell (1774-1842) circulated a privately printed pamphlet, "An Idea of a New Anatomy of the Brain." In this occurred this passage: "On laying bare the roots of the spinal nerves I found that I could cut across the posterior fasciculus of nerves which took its origin from the posterior portion of the spinal marrow without convulsing the muscles of the back, but that on touching the anterior fasciculus with the point of the knife the muscles of the back were immediately convulsed." In his work "The Anatomy of the Human Body" (7th edition) he admitted that sensibility is indeed seated in the nerves, but that is only one of their functions. There are nerves which possess no sensibility at all. He was led to surmise this difference of function by observing beforehand differences of structure, being early struck by the perfect regularity of the spinal nerves as contrasted with the very