572 THE POPULAR SCIENCE MONTHLY 



betes would be produced. Thus, the discovery which he made was not 

 the result of a " haphazard dive in Nature's full pocket " but came from 

 a carefully planned experiment. As was often the case, the investiga- 

 tion did not yield the expected results, but something equally valuable. 



He fed a diet rich in sugar to a dog, killed it at the height of diges- 

 tion and examined the blood leaving the liver by way of the hepatic 

 vein to see if the liver caused a destruction. An abundance of sugar was 

 found here. To see if this was the sugar which had been fed, the experi- 

 ment was repeated, giving the dog only meat. To his great surprise, an 

 abundance of sugar was again found in the hepatic vein and very little 

 in the blood from the other organs. He immediately divined the truth 

 that the liver makes the sugar which was found in such large amounts. 

 Repetition of the experiments with many modifications always produced 

 the same results. The sugar was shown to be dextrose. Different ani- 

 mals showed the same phenomenon. These results were published in 

 1849-50, when he described the sugar production by the liver as similar 

 to a secretion and not influenced by the kind of food eaten. 



These observations, confirmed by others, established the glycogenic 

 function of the liver ; that is, they proved that the liver produces sugar 

 by a mechanism similar to secretion. Going further, he showed that 

 the sugar is not made from substances in the blood flowing through the 

 liver, but from a substance present in the liver tissue. This was 

 demonstrated by washing out all the blood and sugar from an isolated 

 liver. After letting it stand for some time in a warm place, more sugar 

 could be washed out with water. Boiled liver tissue did not react in this 

 way, but if a small amount of fresh liver decoction was added to the 

 boiled tissue, sugar was produced as before. This experiment showed 

 that the sugar was formed by enzyme action from something present in 

 the liver tissue. He isolated this substance and showed it did not give 

 the tests for dextrose, but was easily changed into it by fermentation. 

 These results were announced to the Academie des Sciences on Septem- 

 ber 24, 1855. Two years later, he obtained the substance in a pure state 

 and gave it the name "glycogen." Analysis showed it to be a carbo- 

 hydrate. 



Bernard believed the formation of glycogen in the liver to be a vital 

 process, but the formation of dextrose from glycogen to be a simple 

 enzyme action independent of life. This was contrary to the teaching of 

 the time, for all enzyme actions were considered to be inseparable from 

 the living cell. He showed that the blood contains an enzyme capable 

 of forming dextrose from glycogen and suggested that a nervous control 

 of the circulation governs the sugar formation. Comparisons were 

 drawn between the formation of glycogen and sugar in the animal body 

 and starch and sugar in plants. 



While work was continued along this line, the fundamentally im- 



