60 PHYSIOLOGICAL CHEMISTRY 



stances. Cellulose also is found in certain lower animals, the 

 tunicates. Cellulose is insoluble in the ordinary solvents. It 

 dissolves, however, in Schweizer's reagent, an ammoniacal solu- 

 tion of copper oxide, and in some other reagents. Cellulose 

 derivatives are extensively used in the arts. Thus nitrocellu- 

 loses of varying composition are used in the manufacture of ex- 

 plosives, collodion, celluloid, artificial rubber, etc. From cellu- 

 lose artificial silk and artificial gutta percha also are prepared. 



There has been much discussion as to whether cellulose is of 

 value as a food. Undoubtedly this is the case in herbivora. In 

 man it probably is of little food value, but serves a useful pur- 

 pose in giving bulk to the food and thus stimulating the mus- 

 cular activity of the intestine. It has been stated that the cellu- 

 lose of young and tender lettuce, asparagus, etc., may be utilized 

 by the body to a considerable extent as food. There is no enzyme 

 in the digestive juices capable of hydrolyzing cellulose, so that 

 its disintegration must be due to the action of intestinal bac- 

 teria. 



Glycogen. Glycogen is found in the organs and tissues of 

 animals, and also in some plants (yeast). It serves as a reserve 

 fuel or food supply. The chief depots for glycogen deposit 

 are the liver and the muscles. Glycogen is found in oysters, 

 scallops and other molluscs. Glycogen may be prepared from 

 the liver of an animal which has just been killed. The liver is 

 ground in a mortar with sand, and extracted with boiling water 

 slightly acidified with acetic acid. If the extraction is not made 

 at once after the death of the animal the glycogen supply will 

 be greatly diminished or disappear altogether, as it is rapidly 

 hydrolized to glucose by enzymes in the liver tissue. Feeding 

 rabbits for a day or two on carrots before killing will insure a 

 liberal supply of glycogen in the liver. 



Glycogen is a white amorphous powder, which dissolves in 

 cold water forming an opalescent solution. This solution gives 

 a wine red or brown color with iodine. It does not reduce Feh- 

 ling's solution, is not fermented by yeast, and is dextrorotatory. 

 On boiling with dilute acids, glycogen is hydrolyzed to glucose. 



