Chap, iv.] METABOLIC PROCESSES OF THE BODY. 571 



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 glyco- 

 gen 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 be- 

 tween these two views. It may be that both views are true, 

 or rather that the true conception embraces both views. It 

 may be that the normal metabolism of the hepatic cell does pro- 

 duce 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 conversion into glycogen is a subsidiary act for the purpose 

 of retaining the carbohydrate material in the grasp of the cell. 

 If this be the case, then until it has been shewn that there is 

 something peculiar about the sugar thus produced by the cell 

 itself, by virtue of which it alone can be converted by the cell 

 into glycogen, we may fairly infer that the cell might also 

 convert into glycogen sugar passing into the interstices of the 

 cell-substance from the portal capillaries. 



§ 366. We may now turn to another question, the answer 

 of which is in a measure dependent on the one wdiich we have 

 just discussed. What is the use and purpose of this hepatic 

 glycogen ? What ultimately becomes of the glycogen thus for 

 a while stored up in the liver? 



One view which has been put forward is as follows. We 

 have evidence, as we shall presently learn, that a great deal of 

 the fat of the body is not taken as such in the food, but is 

 constructed anew in the body out of other substances. Both 

 carbohydrates and proteids, taken in excess or under certain 

 circumstances, lead to an accumulation of fat ; and we have 

 reason to believe that carbohydrates on the one hand and the 

 carbon-holding portions of various proteids on the other, may 

 by some process or other be converted into fat. And it has 

 been suggested that the glycogen in the liver is a phase of a 

 constructive fatty metabolism, that it is material on its way to 

 become fat. There is, however, no positive evidence in favour 

 of this view. 



