1 68 THE CARBOHYDRATES 



bottom. After an hour or two the cells begin to rise, and they 

 become distributed throughout the medium after the lapse 

 of four or five hours. The fermentation is now much more 

 active, and the amount of glycogen in the cells less. The next 

 five to fifteen hours is the period of maximum vegetative 

 activity, during which the glycogen disappears ; then it slowly 

 reappears, and later on much more rapidly, at which phase 

 there is a marked decrease in budding. At the height of 

 fermentation, or immediately after, the glycogen increases 

 rapidly, and a large number of cells sink to the bottom of 

 the fluid. If the medium be not exhausted, the process may 

 be repeated two or three times. 



These facts suggest that the yeast, although surrounded 

 by a medium rich in soluble carbohydrate, uses its glycogen 

 reserve in the first instance and, moreover, is not able to 

 utilize the free sugar without first elaborating it to glycogen 

 and mannan. Elias and Weiss * find that the reaction of 

 the nutrient medium has a bearing upon the amount of 

 glycogen produced, there being a marked increase in the 

 presence of alkali. 



Although glycogen and mannan may be looked upon as a 

 temporary reserve food.f for yeast-cells rich in glycogen retain 

 their vitality much longer than those in which there is little 

 or none, the fact that in the spores of species of Mucor and in 

 sclerotia glycogen does not appear until growth has com- 

 menced, points to the conclusion that in these plants, at any 

 rate, it is not primarily a storage product. Kohl considers 

 that since it is more abundant in Saccharomyces during active 

 gemmation, it is not exclusively a reserve substance, but an 

 intermediate product in the formation of alcohol from the 



sugar. 



In the animal kingdom, according to Hoppe-Seyler, glyco- 

 gen is an invariable constituent of almost all developing cells ; 

 it is found also in the muscles and blood, and chiefly in the 

 liver, where it is stored in larger quantities. 



It may be remarked that there is little doubt that the 

 glycogen obtained frdm'animal and plant sources are identical. 



* Ellas and Weiss : " Biochem. Zeit.," 1922, 127, i. 

 t See Warkany : id., 1924, 150, 271. 



