TAXONOMY 
253 
This method of nutrition is called saprophytic, 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 
