308 PHYSIOLOGICAL CHEMISTRY. 



proteins with the sugar group of the gluco-proteids, but casein 

 and gelatin fed to animals lead also to production of glycogen, 

 and these bodies in pure condition do not furnish a sugar com- 

 plex by laboratory treatment. In addition to this it is im- 

 possible that the sugar group could be abundant enough in the 

 other common proteins to account for the large amount of 

 glycogen which may be formed by protein diet. These facts 

 lead to the view that a synthesis must be concerned in the 

 reaction. Such protein derivatives as leucines, the hexone 

 bases and other bodies have been thought of as leading pos- 

 sibly to the end, but direct experiments with animals have 

 given no satisfactory proof of such a hypothesis. For the 

 present, therefore, the method of production from proteins 

 must be left without explanation. 



A diet of fat leads also to glycogen accumulation or forma- 

 tion in small amount, according to some recent observations. 

 This latter reaction requires some kind of an oxidation and is 

 more difficult of explanation than the other. It must be re- 

 membered that an accumulation of glycogen may follow from 

 diminished destruction as well as from increased production, 

 and where the amount in question is small, an apparent in- 

 crease may be traced to errors of observation or experiment. 

 In a mixed diet it is practically impossible to trace the effect 

 of any one substance. The behavior of pentoses is an illus- 

 tration; according to the statements of some authors these 

 carbohydrates increase glycogen. It may be, however, that 

 they simply behave as sparers of glycogen by undergoing oxi- 

 dation, which otherwise the glycogen would have to undergo. 



Not all the carbohydrate reaching the portal vein is trans- 

 formed in the liver; apparently only a certain portion is so 

 changed, while the excess is stored up temporarily in other 

 organs. This is evident from the fact frequently observed in 

 animal experiments that the amount of glycogen in the liver 

 is below what should be expected from the food when this is 

 excessive in carbohydrates. With ordinary or deficient feed- 

 ing the liver doubtless is able to store as glycogen all the sugar 



