TAXONOMY 



253 



This method of nutrition is called saprophy tic, and the yeast plant 

 is said to be a saprophyte. 



A striking fact must be briefly mentioned in connection with the 

 metabolism of yeast. Many organisms exercise a profound effect 

 on the medium in which they live. Yeast causes a wholesale destruc- 

 tion of sugar in the surrounding fluid. One of the decomposition 



FIG. 126. Yeast, Saccharomyces cerevisice, the variety known as brewers' bot- 

 tom yeast; a, spore formation; b, elongated cells. (After Schneider, Pharmaceu- 

 tical Bacteriology.) 



products of sugar is alcohol. The alcohol of commerce is produced 

 by the activity of this plant. 



Saccharomyces has its times of danger and stress when the cells 

 perish in great numbers from cold, starvation, poisons, etc. If not 

 too suddenly exposed, however, they are able to meet adverse con- 

 ditions by eliminating most of their water, suspending physological 



