THE HISTORY OF GLYCOGEN. 445 



glycogen in a solid form, filling up the vacuole. Again, as we have inci- 

 dentally mentioned, sugar injected into the jugular vein readily gives rise to 

 sugar in the urine ; but a very considerable quantity can be slowly injected 

 into the portal vein without any appearing in the urine. This suggests the 

 idea that the liver, so to speak, catches the sugar as it is passing through 

 the hepatic capillaries and at once dehydrates it into glycogen. 



Similar consideration may also be applied to the case mentioned above of 

 the appearance of glycogen in the hepatic cells of winter (fasting) frogs. 

 We have reason to think that sugar makes its appearance as a product of 

 the metabolism of various tissues. The sugar thus arising finding its way 

 into blood may be made use of at once elsewhere, converted speedily, for 

 instance, into carbonic acid and so got rid of. But we can readily imagine 

 that uuder certain circumstances, as for instance when the activities of the 

 animal were lessened by a low temperature, it was not so made use of and 

 remained in the blood. If so, it would in the course of the circulation be 

 carried to the liver, and might be at once taken up by the hepatic cells and 

 converted into glycogen ; ' and these might be so active that the blood was 

 never at any time allowed to remain loaded with sugar to such an extent as 

 to permit a loss through the urine. 



381. Upon such a view, the carbohydrate taken as food would be 

 converted into glycogen by the agency of the hepatic cell, without at any 

 time becoming an integral part of the living substance of the cell. Such a 

 view may be the true one ; but it is open for us to look at the matter in 

 another light. We may push still further the analogy between the glycogen 

 of the hepatic cell and the material with which a secreting cell is loaded. In 

 dealing with secretions we saw reasons for regarding such a body as mucin 

 to be a product of the metabolism of the cell substance of the mucous cell ; 

 and we may similarly regard glycogen, or sugar readily convertible into 

 glycogen, or at least some or other carbohydrate material, as a normal pro- 

 duct of the metabolism of the hepatic cell. We may thus conceive of the 

 hepatic cells as being continually engaged in giving rise to carbohydrate 

 material in the form either of sugar or of some other body ; and we may 

 suppose that under certain circumstances, as in the absence of adequate food, 

 the carbohydrate material thus formed is at once discharged into the blood 

 of the hepatic vein for the general use of the body, but that under other 

 circumstances, as when an amylaceous meal has been taken, the immediate 

 wants of the economy being covered by the carbohydrates of the meal, the 

 carbohydrate products of the hepatic metabolism are stored up as glycogen. 

 Under such a view the sugar of the meal is used up somewhere in the body, 

 and the glycogen to the storage of which in the liver it gives rise comes 

 direct from the hepatic substance. And a similar explanation may be given 

 of the storing-up of the glycogen in the liver under such circumstances as 

 those of the winter frog previously mentioned. 



We do not possess at present experimental or other evidence of so clear 

 a kind as to enable us to decide dogmatically between these two views. We 

 have seen that proteid food, though in this respect falling far below carbo- 

 hydrated food, does or may give rise to a certain amount of glycogen in the 

 liver ; and gelatin seems to have the same effect. Further, in certain cases 

 of the disease diabetes, of which we shall have to speak presently, and which 

 is characterized by the presence of a large amount of sugar in the blood, 

 sugar continues to be formed in large quantity, even when the diet is re- 

 stricted to proteid and fatty matters, all carbohydrates being excluded. 

 Now in diabetes we have reason to believe that the large quantity of sugar 

 in the blood is accompanied by a large deposition of glycogen in the liver, 

 and indeed in other tissues ; for in the few cases which have been examined 



