CHEMISTRY OF THE LIVER. 3O/ 



tion of the sugar takes place in the blood after a meal it must 

 follow that it or some derived reserve product must be tem- 

 porarily retained somewhere. The place of this retention is 

 the liver and the form in which the sugar is held is glycogen. 

 The chemical reactions of glycogen have been discussed in the 

 chapter on the carbohydrates, but in this place other relations 

 must be considered. Xo simple answer can be given to the 

 question as to the method of formation of glycogen from 

 sugar. Although the formula is commonly written C 6 H 10 O 5 , 

 it is, like common starch, certainly a multiple of this. Hence 

 a simple equation connecting glucose and glycogen of the 



form 



GH 12 O H 2 O = C 6 H 10 O 5 



is not strictly correct. Besides, several other facts appear 

 which complicate the problem. While glucose is ordinarily 

 the sugar which passes through the portal vein, other sugars 

 are also consumed and in the digestive process do not become 

 changed to glucose. From cane sugar we have some fructose 

 and from milk sugar some galactose, and with these in the 

 food it appears that glycogen is still formed. Moreover it 

 has been shown that substances not carbohydrate at all may 

 give rise to glycogen. Animals have been starved until the 

 liver was practically free from glycogen (as known by pre- 

 vious trials with other animals) and then fed on fibrin or 

 washed out lean meat. On killing the animals a short time 

 later a store of glycogen was found in the liver, indicating its 

 formation from something in the protein. With such facts 

 in mind it is not possible to form any simple theory of the 

 production of the reserve substance. From the sugars it is 

 likely that some such reaction takes place as occurs in the 

 formation of starch in plants. The carbohydrate built up in 

 the plant from water and carbonic acid is a sugar and this is 

 transformed by some enzymic reaction into starch as a reserve 

 material. The mechanism of this change, however, is quite 

 obscure. 



Attempts have been made to connect the formation from 



