128 THE CARBOHYDRATES 



If healthy brewers' yeast be added to Pasteur's solution the 

 cells, which contain much glycogen, sink to the bottom. After 

 an hour or two the cells begin to rise, and they become dis- 

 tributed 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 im- 

 mediately 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. 



Although glycogen may be looked upon as a temporary 

 reserve food-matter, 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, gly- 

 cogen 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 from animal and plant sources are identical. 



Preparation. 



The following method of obtaining glycogen was devised 

 by Pfliiger.* Fresh finely-cut liver is stirred* up with water 

 and 60 per cent caustic potash, and heated for two hours ; the 

 filtered solution, containing 15 per cent of potash, is then 

 mixed with an equal volume of 96 per cent alcohol, and the 



* Pfluger : " Pfliiger's Archiv f. Phys.," 1902, 91, 119, and 1903, 93, 163. 



