We owe, of course, to the investigations of Laënnec our knowledge of the various râles and their diagnostic significance. In his classic description of lobar pneumonia we find the stages revealed by post-mortem examination coupled with the physical signs the early crepitant râle, and the mucous râle that accompanies resolution. He held that a metallic tinkle could be heard in hydro-pneumothorax or pyo-pneumothorax. Surpassing the work of Bichat he gave a masterly description of bronchitis with its sonorous and sibilant râles. He described also the râle humide and the souffle. We are indebted to Laënnec for descriptions of bronchiectasis, oedema of the lungs, pulmonary "apoplexy," hæmorrhagic pleurisy, gangrene of the lungs and emphysema. It seemed to him that vesicular emphysema is, next to hypertrophy, the simplest of all the organic lesions of the lungs, since it consists merely in the dilatation of the air cells. On this account it remained long unknown, and had, he thought, not been correctly described by any author before his time. "I," he continues, "for a long time thought it very uncommon, because I had observed only a few cases of it; but since I have made use of the stethoscope, I have verified its existence as well on the living as the dead subject, and am led to consider it by no means infrequent." In some cases the lung takes on a striking resemblance to the vesicular lungs of Reptilia.

It did not occur to Laënnec to make use of the stethoscope in the diagnosis of pregnancy. This idea came first to his friend Dr. Kergaradec while verifying the facts contained in the first edition of "Mediate Auscultation." Dr. Kergaradec's conclusions are stated in the appendix of the second edition of that work. In putting his idea to the test he observed the fœtal heart-beat, as well as the placental bruit, in a woman very near her confinement. The latter he described as an arterial pulsation accompanied by a bellows sound. The fœtal pulse, which is distinctly audible in the sixth month and sometimes a little earlier, is usually twice as rapid as that of the mother. The placental sound, which is usually perceptible about the fourth month, is, on the other hand, isochronous with the pulse of the mother.

"Laënnec," says Osler, "laid the foundations not only of our modern knowledge of tuberculosis, but of modern clinical medicine." By the invention of the stethoscope he brought into play one of the higher senses and armed the profession with the means of a more adequate diagnosis. He did not underrate his own achievement, holding, as he did, to the Hippocratic conviction that theory must rest on observation, and adopting as the motto of his work: An important part of the art is in my judgment to be able to explore (μέγα δὲ μελός ἡγευμαί τῆς τεχνῆς εἶναιτὸ δυνάσθαι σκοπεῖν). Very much of

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 particular 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