NUTRITION 225 



11. The hoarding of inactive food material. II. The storage 

 of glycogen. In many cells of the body, but especially in 

 those of the liver and to a less extent in those of the skeletal 

 muscles, there is found a carbohydrate substance known as 

 glycogen. This substance belongs to the same group of car- 

 bohydrates as starch and dextrines (see Chap. VIII), and is 

 sometimes called animal starch. Like them it is changed into 

 sugar by the action of saliva and pancreatic juice, whence its 

 name (7X1^5, "sweet"; -yevrjs, "former"). The same change 

 occurs on the death of the cells in which it is contained, 

 the sugar thus formed giving to such tissues a sweetish 

 taste. This is often noticed, for example, in liver and in 

 scallops (the shell muscle of Pecteri). The total amount 

 of glyeogen in the human body may exceed 700 grams 

 (13 ounces), one half of which is concentrated in the 

 liver and the other half scattered about in the other tissues 

 of the body. 



Experiments have shown that glycogen is not formed from 

 the fat in food ; that it is formed in small quantities from pro- 

 tein; while its chief source is the carbohydrates of the food. 



The blood may be said to be always sweet, its constant 

 percentage of sugar (1 to 2 grams per 1000 cubic centimeters 

 or 0.05 ounce per quart of blood plasma) being a striking 

 fact, and one that we should hardly have anticipated. One 

 might suppose that the sugar in the blood would increase, 

 as does the amount of fat, during active digestion and ab- 

 sorption, and that after digestion had ended, it would 

 diminish. As a matter of fact the amount of sugar in the 

 blood remains practically constant both during and after 

 the completion of digestion, and this despite the fact that 

 the tissues are constantly abstracting sugar from the blood. 

 Evidently the blood must be supplied with sugar from some 

 other source than the alimentary canal, and there must be 

 somewhere in the body a compensating mechanism controlling 

 the sugar supply of the blood. 



