440 



THE METABOLIC PROCESSES OF THE BODY. 



lation of glycogen in the liver. We may remark that the greatest accumu- 

 lation of glycogen is effected not by a pure carbohydrate diet, but by a 

 mixed diet rich in carbohydrates. A quantity of carbohydrate mixed with 

 a certain proportion of proteid gives rise to a larger amount of glycogen in 

 the liver than the same quantity of carbohydrate given by itself; and it is 

 possible that the presence of an appropriate quantity of fat still further 

 assists the accumulation. But this result probably depends, in part at 

 least, on the fact that, though differences may be met with in different ani- 

 mals, a mixture of the several classes of food-stuffs is more readily digested, 

 resulting in more nutritive material being thrown upon the blood, than is a 

 meal consisting exclusively of one kind of food-stuff alone. 



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 car- 

 bohydrates 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 con- 

 trary. 



The storing-up of glycogen in the liver is also influenced by other circum- 

 stances than the taking of food. For instance, in the frog an increase of 

 glycogen takes place during the winter months. In the summer months the 

 liver of a frog will be found to contain very little glycogen (Fig. 114, C), 



FIG. 113. 



Section of Liver of Frog. (Langley.) The figure shows the tubular structure of the liver. At 

 a, a tubule is seen in transverse, at b in longitudinal section ; I, lumen of tubule. The liver was 

 that of a winter frog, and the cells show an inner zone of proteid granules ; the outer zone was 

 chiefly occupied by glycogen. 



unless the animal has been unusually well fed ; whereas a liver examined in 

 midwinter (Figs. 113, 114, A) will be found to contain a considerable quan- 

 tity, even though no food has been taken for months. In such a case the 

 material for the formation of the glycogen in the liver must have been fur- 

 nished by some part of the body of the frog, and could not, as may be the case 

 when a *meal leads immediately to an increase of glycogen, be supplied 



