312 PHYSIOLOGY 



theory is substantiated by the fact that on feeding urea mixed 

 with alimentary protein, the formation of glycogen increases, 

 although the urea is eliminated again, and cannot play any part 

 in the formation of the glycogen. His argument does not, 

 however, carry conviction, because he gives no direct proof of his 

 thesis. 



Other undeniable facts can be mustered in support of 

 Seegen's position. Voit noticed that even after 80 days' torpor 

 the liver of the marmot contains a large amount of glycogen, 

 which can, he says, only be explained on the assumption that the 

 liver during hibernation goes on forming glycogen at the expense 

 of the proteins which the animal has at its disposal. Kiilz, 

 however, denies this interpretation, and maintains that the 

 glycogen fouud by Voit is the residue of that formed in previous 

 feeding, the consumption of which is arrested during hibernation. 

 He killed four marmots at different intervals after the commence- 

 ment of torpor, and found approximately the same amount of 

 glycogen in the liver. In our opinion this fact does not, however, 

 preclude the possibility that glycogen is slowly formed during 

 hibernation, in quantities approximately equal to what is simul- 

 taneously consumed. The argument of Kiilz may be met by 

 another apparently enigmatical fact, which Aducco noticed in 

 1889 on pigeons that were kept in the dark and starved. The 

 glycogen regularly disappeared from the liver in the first days of 

 fasting, but reappeared in the succeeding days in considerable 

 amount. There seems but one rational interpretation of this 

 phenomenon. In the first days of inanition, when tissue meta- 

 bolism is still fairly active, the amount of glycogen consumed 

 much exceeds that simultaneously formed, so that the reserve of 

 this material is entirely exhausted. In the subsequent days of 

 starvation, on the other hand, when general metabolism is greatly 

 retarded, the quantity of glycogen formed is greater than that 

 simultaneously consumed, so that a new store accumulates in 

 the liver. 



By an identical process the hepatic cells of the frog accumulate 

 a large amount of glycogen during the winter, while in summer, 

 when metabolism is very active, they contain hardly any, since 

 it is consumed as fast as it is formed (Langley). As the intensity 

 of general metabolism in the frog (and in cold-blooded animals 

 generally) depends on the external temperature, it is easy to 

 reduce or entirely abolish the glycogen accumulated in the liver 

 of a hibernating frog, by exposing it for some time to a temperature 

 of 20-22 C. Conversely, it is possible to obtain a certain amount 

 of glycogen from the liver of a summer frog after exposing it for 

 several days (Fig. 98) to a very low temperature. 



It is evident that the accumulation of glycogen in the hepatic 

 cells during natural or artificial torpor does not depend on 



