GLYCOGEN. 9 



the liver, but it is usually not more than 3 or 4 per cent. 

 It disappears completely from the liver after long starva- 

 tion, or more quickly through severe work or great fright. 



It is best obtained from the liver. After boiling to kill 

 the ferments which are always present, dissolving in water, 

 and removing the nitrogenous substances, it can be pre- 

 cipitated by alcohol. 



Glycogen is an amorphous, white, tasteless powder. 

 In water it dissolves to an opalescent solution. With iodin 

 it gives a red color, which disappears on heating. It does 

 not have a reducing action upon cupric hydrate. Boiling 

 with acids converts it into dextrin, then maltose, then glu- 

 cose. The salivary and pancreatic ferments produce the 

 same change. 



The glycogen of the liver seems to be formed mostly 

 from the carbohydrates of the food, but partly, at least, 

 from the nitrogenous compounds. 



It is deposited in the liver as a reserve material, just 

 as the starch is stored for a reserve material in the plants. 

 When it is needed by the body it is converted by a ferment 

 into grape-sugar, and this passes into the circulation. It 

 is probable that it is used to furnish energy for the body. 

 After death the glycogen quickly disappears from the tis- 

 sues of the body, being decomposed by the ferments which 

 are present. If these are destroyed by boiling the tissue 

 for a short time the glycogen is not destroyed, but can be 

 extracted. 



15. PREPARATION OF GLYCOGEN. In a mortar grind with 

 sand or glass about 25 grammes of the adductor muscle of the 

 scallop (pecten irradiens), extract several times with 50 cubic centi- 

 meters of cold water, repeating the operation with hot water. 

 Boil the liquid to coagulate the proteins, filter and concentrate the 

 nitrate to about 50 cubic centimeters, then add alcohol to 70 per 

 cent, in strength. This precipitates the glycogen. Filter this off. 



