HISTORY OF DIFFERENT FOODSTUFFS IN BODY 1039 



sugar-content of the former is markedly raised. 1 These facts imme- 

 diately suggest that some barrier is interposed which prevents the newly 

 absorbed sugar from entering the general circulation. This conclusion 

 is also upheld by the fact that extracts of the livers of animals which 

 had been killed some time beforehand, contained a large quantity of 

 reducing sugar, while those of washed livers exhibited an opalescence 

 which was proved to be caused by the presence of a polysaccharide, 

 known as glycogen (C 6 HioO 5n ). When an extract of this kind is treated 

 with alcohol, it yields an abundant precipitate which may be con- 

 verted into sugar by hydrolysis with a mineral acid. This conversion 

 also takes place in pieces of liver which have been allowed to stand for 

 some time, so that their yield of glycogen gradually becomes less, 

 while their content in glucose increases. In either case, this glyco- 

 genolysis proves that the hepatic cells must contain some enzyme 

 which is capable of effecting this transformation. The name of 

 glycogenase has been applied to it. 



After an abundant intake of carbohydrates glycogen may be 

 present in the liver in as large amounts as 12 per cent, of the weight 

 of the fresh organ. It is demonstrable here in the form of hyalin 

 chips which give a characteristic port-wine color with iodin; more- 

 over, a liver of this kind is large, soft and easily injured. But while 

 the chief source of glycogen is the assimilable carbohydrate material 

 of the food, namely, glucose, fructose, galactose and mannose, it may 

 also be formed from proteins or the products of their decomposition. 

 Whether this conversion takes place under normal conditions cannot 

 be stated with certainty, although it is known that a starving animal 

 may employ this means to retain a certain store of sugar. Thus, 

 it will be found that the liver of an animal during starvation contains 

 only a very small amount of glycogen, whereas its blood sugar, al- 

 though less than normal, has not disappeared altogether. This rem- 

 nant of liver-glycogen, however, may be removed without difficulty 

 by supplementing the starvation with muscular work. Inasmuch as 

 no carbohydrates are ingested during this period, and inasmuch as 

 the glycogen of the liver and muscles has been used up, it is evident 

 that some sugar, or a substance similar to it, must have been formed 

 from the proteins. This deduction seems justified, because no evi- 

 dence has been presented as yet to show that glycogen may also be 

 derived from the fats. Further, if an animal whose store in glycogen 

 has been exhausted, is fed with washed fibrin, caseinogen, or even 

 amino-acids, the liver will be found to have acquired glycogen. This 

 substance also quickly disappears if the starving animal is thrown into 

 convulsions by means of strychnin. If these spasms are stopped 

 later on by the administration of chloral, a certain amount of glycogen 

 is again found in the liver, derived in all probability from the tissue 

 proteins. 



1 McLeoud and Fulk, Am. Jour, of Physiol., xlii, 1917, 193, and Dakin, Oxida- 

 tion and reduction in the animal body, Monogr. in Biochem., 1912. 



