CHAP v.j NUTRITION. 419 



stand out prominently as the substances which taken as food lead 

 to an accumulation of glycogen in the liver. As far as we know 

 at present the glycogen which thus appears in the liver as the 

 result of feeding either with any of the various forms of carbo- 

 hydrates, or with proteids, or with other substances, is of the same 

 kind and presents the same characters; at least we have no 

 evidence to the contrary. 



The question naturally arises, 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 carbo- 

 hydrates on the one hand and the carbon-holding portions of 

 various proteids, 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. 



The positive evidence in favour of this view is very scanty ; it 

 is almost limited to the facts that fat, sometimes in very large 

 quantity, is found in the hepatic cells, that while fat itself taken 

 as food leads to no increase in the hepatic glycogen, carbo- 

 hydrates, which are especially fattening, are most active producers 

 of glycogen, and that the fat present in the hepatic cells seems 

 to be increased by such diets as naturally increase the glycogen 

 in the liver. No evidence has been offered as to the several 

 steps of the conversion of glycogen into fat, nor indeed has 

 it been suggested what those steps are. The view indeed is 

 almost exclusively based on the supposed proof that the blood 

 of hepatic vein contains during life no sugar, or at least not 

 more than does the general blood or even the blood of the portal 

 vein. From this it is inferred that the glycogen in the liver is not 

 lost to the liver by becoming converted into sugar and so discharged 

 into the hepatic blood and therefore must be converted into some 

 other substance which substance is presumably fat. Bernard both 

 in his earlier and later researches maintained that the blood of 

 the hepatic vein under normal conditions is richer in sugar than 

 the blood of the portal vein or indeed of any other part of the vas- 

 cular system ; this he regarded as an indication that the liver is 

 always engaged in discharging a certain quantity of sugar into the 

 hepatic veins; and his views have been accepted by many observers. 

 On the other hand others maintain that the blood in the hepatic 

 vein, if care be taken to keep the animal in a perfectly normal 

 condition, contains no more sugar than does the blood of the right 

 auricle or of the portal vein, and indeed that the liver itself, if 



272 



