INTERNAL KESTITUTIVE SECRETIONS 



313 



alimentation, since the hibernating frog entirely abstains from 

 food. Under these conditions, therefore, the glycogen cannot be 

 formed at the expense of the carbohydrates ; in all probability it 

 is formed by cleavage of the protein molecule, on which the carbo- 

 hydrate groups are liberated from the nitrogenous groups. 



It is, further, not impossible that under these or similar 

 conditions, in which glycogen and sugar are formed independent 

 of the alimentary carbohydrates, part at least of these products 

 may arise from cleavage of the fat molecule with absorption of 

 oxygen. According to Bunge, this hypothesis is supported by the 

 fact that the blood of animals in protracted inanition (when the 

 glycogen store is exhausted) always contains a small and almost 



A. 



m 



FIG. 98. Hepatic cells of frog, fixed with 1 per cent osinic acid in three different phases. 

 A, during hibernation; B, after keeping the frog in winter for 10 days at a temperature of 

 22 C.; C, after keeping it a long time in summer without food. (Langley.) In A the cells are 

 very large, with much homogeneous substance which consists of glycogen, diffused throughout 

 the cytoplasm. The protein granules are collected in the inner zone, particularly round the 

 bile canaliculi ; the outer hyaline zone, on the contrary, contains a number of fat-globules. In 

 B the cells are smaller and contain little glycogen, while the protein granules are diffused 

 throughout the cytoplasm. The hepatic cells of a well-nourished summer frog present a 

 similar aspect. In Cthe cells are much smaller, the cytoplasm is reduced to a minimum, and 

 is almost free of glycogen, with protein granules diffusely distributed ; the nuclei, on the other 

 hand, are larger. 



constant quantity of sugar, and that under these conditions the 

 consumption of nitrogenous substances is minimal, while the fat 

 reserves are being rapidly exhausted. 



In support of the possible derivation of sugar from fat, Bunge 

 brings forward the argument that this origin has long been 

 familiar in plant physiology. In 1859 Sachs demonstrated that 

 the fat disappears from oily seeds set in the dark to germinate, 

 in proportion as starch, gum, sugar, and cellulose were formed. 

 Wiesner further demonstrated that absorption of oxygen accom- 

 panies and is a necessary condition of this conversion of fat into 

 carbohydrates. 



Chauveau adduced the following evidence to the same effect : 

 (a) injection of glycerol into the intestine causes increase of 

 hepatic glycogen, as demonstrated by van Ueen. (6) During the 

 metamorphosis of the chrysalis of Bombyx mori, fat diminishes 



