94 THE POPULAR SCIENCE MONTHLY 



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 experi- 

 ments, publishing his results in 1849-50. About the same time he dis- 

 covered 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 con- 

 tained 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 re- 

 stored by adding to a decoction of the boiled liver a small quantity of 

 fresh liver infusion. From this he inferred that the glycogenic func- 

 tion 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 com- 

 parisons between income and output, failed to produce anything like the con- 

 viction which was brought home to every one by the demonstration that a sub- 

 stance 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 

 aa 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 



