CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 759 



liver as the result of carbohydrate food, arises by simple dehydra- 

 tion of the sugar brought by the portal blood, or through a more 

 complex metabolism of the hepatic cell, involving the splitting up 

 of some of the proteid constituents of the cell-substance. If the 

 latter be the method employed the deposition of glycogen must be 

 accompanied by a corresponding formation (and discharge) of urea ; 

 with the former method this need not occur. Various observations 

 have shewn that in this respect the different carbohydrates and 

 especially the different kinds of sugar, though they may all give 

 rise to glycogen, and a glycogen apparently identical in its 

 characters in all cases, do not behave in the same way. For 

 instance when dextrose is given to an animal which has been 

 starved until its liver is presumably free from glycogen, the amount 

 of glycogen which is found in the liver within a few hours is much 

 too great to be accounted for by the proteid metabolism taking place 

 during the same time as measured by the amount of urea discharged; 

 we infer that the glycogen has arisen (in part at least) by direct 

 dehydration of the dextrose. When on the other hand galactose 

 (a derivative of milk sugar) is similarly given, the glycogen is no 

 greater in amount than could have been supplied by proteid 

 metabolism. We may conclude then, that in the case of some 

 carbohydrates taken as food, the resulting glycogen may arise by 

 simple dehydration, but that in the case of some other carbo- 

 hydrates it may, and in the case of proteid food must, arise through 

 the more complex proteid metabolism. 



There is another consideration moreover which must be kept 

 in view. Even granted that glycogen arises from proteid metabo- 

 lism, we are not justified in assuming that the proteid metabo- 

 lism giving rise to sugar and so leading to a storage of glycogen 

 in the liver necessarily takes place in the hepatic cells. We may 

 suppose, and indeed have reason to think that it may take place in 

 other tissues, in muscle for instance, and that the sugar so formed 

 in the muscle, being carried through the blood stream to the liver 

 is there converted into glycogen. It is at least probable that, 

 in some cases of diabetes, the sugar j.s produced in the muscles or 

 in tissues other than the liver, and further that the sugar so formed 

 may be temporarily stored up as glycogen in various parts of the 

 body. 



So that on the whole the evidence seems to preponderate 

 in favour of the view that some and perhaps much of the glycogen 

 in the liver comes from the direct dehydration of sugar. And we 

 may to a certain extent combine the two views which we are 

 discussing in the following manner. 



It may be that the normal metabolism of the hepatic cell does 

 produce a certain amount of carbohydrate material ; but if so the 

 probability is that the exact form in which that carbohydrate 

 appears in the first instance in the laboratory of the cell is not 

 that of glycogen but of sugar of some kind or other, and that the 



