io8 THE CARBOHYDRATES 



The glycogen appears in the cells of SaccJiaromyces during 

 the early stages of fermentation as minute refractive granules 

 scattered through the protoplasm ; after a few hours these 

 granules give place to small vacuoles, which in turn are re- 

 placed by one large vacuole, which may occupy the greater 

 space in the cell. According to Harden and Rowland,* this 

 progressive increase in the size of the glycogen-vacuole may 

 result from the formation of some substance, besides carbon 

 dioxide, from the glycogen. 



Wager and Penistonf have shown that the amount of 

 glycogen present is correlated with the periodical fluctuations 

 in the fermentative activity. 



On adding yeast to the nutrient fluid, e.g., Pasteur's solu- 

 tion, fermentation may start at once, in which case it was 

 found that the cells float and contain very little glycogen. 

 On the other hand, the cells may contain much glycogen and 

 sink to the bottom ; in this case fermentation is slow to 

 commence, but gradually increases, and eventually becomes 

 much more active ; also the budding is much rnore extensive 

 as conipared with a yeast which contains but little or no 

 glycogen. 



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 



* Harden and Rowland: "J. Chem. Soc, Lond.," 1901, 79, 1234. 

 t Wager and Peniston : " Ann. Bot.," 1910, 24, 45. 



