Page:Popular Science Monthly Volume 84.djvu/576

572 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 investigation 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 digestion 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 experiment 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 animals 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 Académie des Sciences on September 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 carbohydrate.

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