444 METABOLISM, NUTRITION, AND DIET 



least may be, produced upon a protein diet. The glycogen, when stored in 

 the liver cells, may readily be demonstrated in sections of liver containing it 

 by its reaction (red or port- wine color) with iodine, and, moreover, when the 

 hardened sections are so treated that the glycogen is dissolved out, the proto- 

 plasm of the cell is so vacuolated as to appear little more than a framework. 

 There is no doubt that in the liver of a hibernating frog the amount of glyco- 

 gen stored up in the liver cells is very considerable. 



AVERAGE AMOUNT OF GLYCOGEN IN THE LIVER OF DOGS UNDER VARIOUS. 



DIETS. (PAVY.) 



Diet. Amount of glycogen in the liver. 



Flesh food 7.19 per cent. 



Flesh food with sugar 14 5 per cent. 



Vegetable diet, i.e., potatoes with bread or barley meal. 17 . 23 per cent. 



The dependence of the formation of glycogen on the kind of food taken: 

 is also shown by the following results, obtained by the same experimenter: 



AVERAGE QUANTITY OF GLYCOGEN FOUND IN THE LIVER OF RABBITS AFTER. 

 FASTING, AND AFTER A DIET OF STARCH AND SUGAR RESPECTIVELY. 



After three days' fasting Practically absent. 



After diet of starch and grape sugar 15-4 per cent. 



After diet of cane sugar 16.9 per cent. 



Glycogen is also formed from fats in diabetes, but there is no clear proof 

 that fats increase the amount of glycogen in the cells. Glycerol injected into 

 the alimentary canal may also increase the glycogen of the liver. Recent 

 observations indicate that glycogen may be formed in the turtle liver when 

 perfused with very dilute formaldehyde solutions. The diet most favor- 

 able to the production of a large amount of glycogen is a mixed diet con- 

 taining a large amount of carbohydrate, but with some protein. 



Glycogen is stored in other organs of the body. Of these the muscles 

 are deserving of special mention. The amount of glycogen in the muscles, 

 of young animals is often considerable. The placenta is also a storehouse 

 of glycogen. 



The Destination of Glycogen. The chief theories concerning the 

 use of glycogen in the organism are advanced by Bernard and by Pavy.. 

 The former considers glycogen as a reserve supply of carbohydrate. When- 

 ever the glycogen of the blood is reduced below the normal level, i.e., about 

 o.i to o . 1 5 per cent. , there is a conversion of glycogen into sugar. The sugar 

 enters the blood and passes to the tissues where its oxidation is a source of 

 energy. Pavy considers glycogen to be a stage in the synthesis of carbo- 

 hydrate into fat and protein. Bernard's theory is more generally accepted. 

 It explains more satisfactorily why the sugar content of the blood is so con- 

 stant. The conversion of glycogen to sugar takes place by the action of an 



