674 CHARLES W. HOOPER 



Substances Contributed by the Liver to the Blood 



Carbohydrate as a Hepatic Internal Secretion. The Formation and 

 Discharge of Glycogen. Claude Bernard (a) in 1848 observed that ani- 

 mals, like plants, have the power of forming sugar independent of the 

 nature of food, and stated that this new function resides in the liver. He 

 suggested that the formation of sugar hy the liver is a chemical process 

 directly influenced by the nervous system. He found that the blood of the 

 right heart contained sugar, not only when extracted from a dog fed on 

 sugar, but also when the animal was on a meat diet. Extract of liver was 

 able to reduce Barreswil's reagent and gave rise to alcoholic fermentation. 

 From this he concluded that the liver was the organ capable of forming 

 sugar, independent of that ingested. In 1853 lie stated that he had dem- 

 onstrated the presence of sugar in the liver of mammals, birds, reptiles, 

 fishes, and molluscs. He further proved that the blood of the hepatic 

 veins invariably contained sugar during digestion; that it contained less 

 when digestion was completed ; hardly any after a long fast. After pro- 

 longed feeding of dogs with meat he failed to find sugar in the intestine 

 or in the portal blood. In the hepatic veins and in the liver he found con- 

 siderable amounts. 



In 1855 Bernard established his theory of internal secretion: That 

 the liver has two functions of secretion ; external secretion, which produces 

 the bile which flows to the exterior ; internal secretion, which forms sugar 

 which enters immediately into the blood of the general circulation. 



Hensen (1857) and, shortly after, Bernard (1857) extracted glyco- 

 gen from the liver. Bernard then modified his original belief concerning 

 the direct formation of sugar in the liver and stated that glycogenesis is 

 indirect and consists of two distinct processes: amylogenesis, the forma- 

 tion of glycogen in the living liver tissue and glycogenesis proper, the 

 conversion of glycogen into sugar ln r an enzyme. The fact that the con- 

 version of glycogen into sugar is arrested by heating freshly excised liver 

 tissue in boiling water convinced Bernard that glycogenesis proper (glyco- 

 genolysis) is dependent upon a hepatic diastase. In 1877, by extraction 

 with glycerin he obtained from the liver an enzyme which converts glyco- 

 gen into sugar. Pavy (1894) extracted from the liver an enzyme which 

 determined the conversion of glycogen into glucose. These results were 

 subsequently confirmed by Tebb in 1897 and others. It is probable, there- 

 fore, that the normal conversion of glycogen to dextrose is affected by 

 special enzymes produced in the liver cells. Bernard believed the forma- 

 tion of sugar in the liver to be controlled by the nervous system. In 1858 

 he found that puncturing the floor of the rhomboidal sinus near the apex 

 of the calamus scriptorius was followed by a marked hyperglycemia and 



