tions is an "internal secretion." On the false assumption that the vagus nerve might influence the hepatic secretion, he punctured the floor of the fourth ventricle, and produced what he called artificial diabetes (experimental glycosuria), in 1849. He is considered, in consequence of this, the founder of experimental medicine.

About 1848 he found one day on his laboratory table some rabbits, which had been brought in from the market. He noted that their urine was clear and acid, like that of carnivora. He then fed them herbs, and, as he had anticipated, their urine became turbid and alkaline. After they had gone without food for a considerable time, he fed them cold boiled beef, which, faute de mieux, they ate readily enough. Again their urine became clear and acid. He concluded that all animals fasting are in a sense carnivorous, since they are nourished on their own tissues. In a later experiment the rabbits were killed after a full meal. He found that the lacteals were white in the lower part of the duodenum about 30 centimeters below the pyloris. This struck his attention, as with dogs in similar circumstances he had noted the whiteness of the lacteals at the upper part of the duodenum. He noted that this difference coincided with the fact that in the dog the entrance of the pancreatic duct is quite near the pyloris, while in the rabbit its entrance is very low. The

idea then occurred to him that the pancreatic juice might be the cause of the emulsion of the fatty matter of the food, and thus facilitate its absorption by the lacteals.

Like his master Magendie, Claude Bernard was interested in the action of poisons (for example, curare and carbon monoxide) and had constant recourse to vivisection. Nevertheless, their methods of investigation were in at least one respect contrasted. Magendie called himself a chiffonnier, thus comparing himself, working haphazard in the field of knowledge, with those who go about the town picking up rags, etc. Bernard, on the other hand, always had a definite aim in view, holding an hypothesis essential to successful research, though too agile mentally to neglect the clues that chance threw in his way, and too astute to be blinded by prepossessions. "Put off your imagination," he said, "as you take off your overcoat, when you enter the laboratory; but put it on again, as you do your overcoat, when you leave the laboratory." He thought that one had little chance of finding anything unless he knew what he was looking for, yet in his own investigations he was again and again rewarded by the discovery of the unexpected.

REFERENCES

Bell, Sir Charles: "On the Nerves," Philosophical Transactions, 1821, pp. 397-424.

The Anatomy of the Human Body. 3 vols., seventh edition, 1824. Bernard, Claude: Introduction à la Médecine Expérimentale. 1865.

Leçons sur la Physiologie et la Pathologie du Système Nerveux. 1858.

Flourens, M. J. P.: Memoir of Magendie (translation). Annual Report, Smithsonian Institution, 1866, pp. 91-125.

Foster, Sir Michael: Claude Bernard. (Masters of Medicine.) Hadley, P. B.: "Johannes Müller," Popular Science Monthly, vol. 72 (1908), pp. 513-33.

Hall, Marshall: "On the Reflex Function of the Medulla Oblongata and Medulla Spinalis," Philosophical Transactions, 1833, pp. 635-65.

Stirling, Sir William: Some Apostles of Physiology. 1902.

CHAPTER XII

EMBRYOLOGY AND KARL ERNST VON BAER THE eighteenth century fell heir to two opposed theories concerning the development of the embryo epigenesis, and preformation or predelineation. They were supported by the authority of the two greatest embryologists of the preceding century, Harvey and Malpighi. Harvey had taught that the organism is built up gradually by the addition of part to part. Malpighi, on the other hand, had held that the chick existed preformed before the beginning of incubation. In the latter view two other early microscopists had concurred, namely, Swammerdam and Leeuwenhoek. The first of these, whose works did not become generally known till 1737, had studied the early stages of the development of the frog, and, interested in the metamorphosis of the caterpillar, had observed the parts of the butterfly in the chrysalis. Leeuwenhoek (1632-1723) was the first to describe the spermatozoa. It would seem that the wonders revealed to these early students of microscopy led them to believe that further revelations of minute structures and minute organisms only awaited the development of better instruments and finer technique.

Moreover, as Professor W. M. Wheeler in his admirable lecture on Wolff has indicated, there is a class of mind predisposed to emphasize the static rather than the dynamic, to view phenomena as being rather than becoming, as stable rather than transitional, and to fasten attention on the fixity of forms and species rather than on their transformations.

The investigations of Charles Bonnet (1720-93), and the authority of Haller, also favored, in the eighteenth century, the inclination to believe in the doctrine of preformation. While still a youth, Bonnet reported his observations concerning parthenogenesis in plant-lice, or Aphides. He had seen a single virgin aphis give birth to ninety-four daughters, which without fertilization continued to produce after their kind. Haller declared that no part of the animal frame was made after the other; that all were made together; and that there was no such thing as epigenesis. It follows logically from the doctrine of preformation that the ovum contains a complete animal that awaits the process of unfolding or evolution, and that the mother of the race bore within her all her posterity, preformed creatures impacted in preformed creatures like a series of boxes enclosed in boxes. This theory of emboîtement, was, indeed, definitely taught by Bonnet, Leibnitz and others.