Page:Popular Science Monthly Volume 86.djvu/98

94 liver was not the site of transformation, Bernard changed his mind when he found that the blood from the hepatic vein of another dog fed upon meat only (a sheep's head) was also loaded with grape sugar. Thus it appeared that the liver is a sugar-manufacturing plant, and that its sugar-producing or glycogenic function is in the nature of an internal secretion, a view which he confirmed by many varied experiments, publishing his results in 1849-50. About the same time he discovered that a puncture in the region of the fourth ventricle of the brain in the dog will produce a temporary diabetes (1849), which the later researches of Harvey Gushing and his associates indicate to be a polyuria deriving from the pituitary body. As a simple decoction of the liver substance was always found to contain dextrose, the next step was to ascertain how the liver produced this substance at the expense of the materials sent from the alimentary canal. After perfusing a freshly excised liver until the wash-water from the hepatic vein contained no sugar, Bernard found that if the liver were left in a warm place for a few hours a subsequent perfusion would once more come out loaded with sugar, and, although this property of the hepatic tissue could be destroyed by boiling, the sugar-producing power could be restored by adding to a decoction of the boiled liver a small quantity of fresh liver infusion. From this he inferred that the glycogenic function is, in effect, a fermentative process and that its agency is a kind of starch. In 1855' he succeeded in obtaining this glycogenic substance in the form of a dry powder, which could be converted into dextrose by fermentation, although it did not itself respond to the sugar tests. In 1857, by his potash-alcohol process, Bernard obtained it in the pure state as "glycogen." It was the fact that glycogen could be seen, touched, tasted and experimented upon as such that established the theory of internal secretions as a working principle in physiology. The epoch-making character of Bernard's discovery is best indicated in the language of Sir Michael Foster, who has given the most fascinating appreciation of his work in medical literature:

The view that the animal body, in contrast to the plant, could not construct, could only destroy, was, as we have Been, already being shaken. But evidence, however strong, offered in the form of statistical calculations, of numerical comparisons between income and output, failed to produce anything like the conviction which was brought home to every one by the demonstration that a substance was actually formed within the animal body and by the exhibition of the substance so formed.

No less revolutionary was the demonstration that the liver had other things to do in the animal economy besides secreting bile. This, at one blow, destroyed the then dominant conception that the animal body was to be regarded as a bundle of organs, each with its appropriate function, a conception which did much to narrow inquiry, since when a suitable function had once been assigned to an organ there seemed no need for further investigation. Physiology, expounded as it often was at that time, in the light of such a conception, was apt to leave in the mind of the hearer the view that what remained to be done consisted chiefly in determining the use of organs such as the spleen, to which as yet no definite