418 GLYCOGEN. [BOOK n. 



Formation and Uses of Glycogen. The amount of glycogen 

 present in the liver of an animal at any one time is largely 

 dependent on the amount and nature of the food previously taken. 

 When all food is withheld from an animal, the glycogen in the 

 liver diminishes, rapidly at first, but more slowly afterwards. 

 Even after some days' starvation a small quantity is frequently 

 still found; but in rabbits, at all events, the whole may eventually 

 disappear. 



If an animal, after having been starved until its liver may 

 be assumed to be free or almost free from glycogen, be fed on 

 a diet rich in carbohydrates or on one consisting exclusively of 

 carbohydrates, the liver will in a short time be found to 

 contain a very large quantity of glycogen. Obviously the 

 presence of carbohydrates in food leads to an accumulation of 

 glycogen in the liver; and this is true both of starch and of dex- 

 trin and of the various forms of sugar, cane, grape and milk 

 sugar. The effect may be quite a rapid one, for glycogen has 

 been found in the liver in considerable quantity within a few 

 hours after the introduction of sugar into the alimentary canal of 

 a starving animal. 



If an animal, similarly starved, be fed on an exclusively meat 

 diet a certain amount of glycogen is found in the liver. This 

 appears to be especially the case with dogs (probably with other 

 carnivorous animals also) ; and in his earlier researches Bernard 

 was led to regard the constant presence of glycogen in the livers of 

 dogs fed on meat, as an important indication of the conversion 

 within the body of nitrogenous into non-nitrogenous material. 

 But in the first place, the quantity of glycogen thus stored up in 

 the liver as the result of a meat diet, is much less than that which 

 follows upon a carbohydrate diet; and in the second place, ordinary 

 meat, especially horse-flesh on which dogs are ordinarily fed, 

 contains in itself a certain amount either of glycogen or some 

 form of sugar. Moreover when animals are fed not on meat but 

 on purified proteid, such as fibrin, casein or albumin, the quantity 

 of glycogen in the liver becomes still smaller, though according to 

 most observers remaining greater than during starvation. We may 

 infer therefore that part of the glycogen which appears in the liver 

 after a meat diet is really due to carbohydrate materials present in 

 the meat. Part however would appear to be the result of the actual 

 proteid food and we have similar evidence that gelatine taken as 

 food leads to the formation of some glycogen in the liver. But in 

 this respect these nitrogenous substances fall very far short indeed 

 of carbohydrate material. 



With regard to fats, all observers are agreed that these lead to 

 no accumulation of glycogen in the liver; an animal fed on an 

 exclusively fatty diet has no more glycogen in its liver than a 

 starving animal. 



Hence of the three great classes of food-stuffs, the carbohydrates 



