THE HISTORY OF GLYCOGEN. 439 



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 shows that the 

 change is not effected 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 glyco- 

 geu is converted is maltose. 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 iOO C., but which is not the action of a 

 ferment capable of being isolated. 



375. 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 glyco- 

 gen in the liver diminishes, rapidly at first, but more slowly afterward. 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 cer- 

 tain 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 forma- 

 tion 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 carbohy- 

 drate diet ; and in the second place, ordinary meat, especially horseflesh on 

 which dogs in such experiments are usually fed, contains in itself ( 62) 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 starva- 

 tion. 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 pro- 

 teid food ; and we have similar evidence that gelatin taken as food leads to 

 the formation of some glycogen in the liver. But in this respect these nitro- 

 genous substances fall far short of carbohydrate material. 



With regard to fats, all observers are agreed that these lead to no accu- 

 mulation 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 stand 

 out prominently as the substances which taken as food lead to an accumu- 



