716 GLYCOGEN. [BOOK n. 



by the temperature of boiling water ; hence the directions re- 

 peatedly given above to throw the liver into boiling water. This 

 naturally suggests the presence in the liver of an amylolytic 

 ferment. But, not only have attempts to isolate from the liver an 

 amylolytic ferment failed, in the hands of most observers at least, 

 but the exact nature of the sugar which appears shews that the 

 change is not affected by an ordinary amylolytic ferment. In the 

 case of the amylolytic ferment of saliva, pancreatic juice, intestinal 

 juice, and indeed of all other amylolytic animal fluids, the sugar 

 into which starch or glycogen is converted is maltose. V^Now the 

 sugar which appears in the liver after death is dextrose, identical, 

 as far at least as can at present be made out, with ordinary 

 dextrose. We are led therefore to infer that the change 

 of glycogen into sugar which appears to go on after death is 

 carried out by some action of the liver, probably of the hepatic 

 cell itself, which is done away with by a temperature of 100 C., 

 but which is not the action of a ferment capable of being isolated. 



455. We have used above the phrase ' well-fed ' animal 

 because the amount of glycogen present in the liver of an animal 

 at any one time is very variable, and especially 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 h'rst, 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 dextrin 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 earlier works on the subject the 

 constant presence of glycogen in the livers of dogs fed on meat 

 was regarded as an important indication of the formation within 

 the body of non-nitrogenous from 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 in such experiments are 



