202 
PHARMACEUTICAL BOTANY 
The cell walls are readily permeable. Food substances diffuse 
through it into the cell, and by a series of changes (which, indeed, 
it is no easy matter to understand) are converted into new living 
substance. The waste products likewise diffuse readily outward. 
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 
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 
processes, and becoming dormant. Sometimes they enter the rest- 
ing condition after a process of division, when each cell divides into 
four parts, each of which becomes nearly dry and is surrounded by a 
thick wall. Such cells are called ascospores, and their production 
serves both as a method of multiplying the plant and of tiding over 
adverse conditions. They can survive for a long time without 
food or water, and can endure higher temperatures than the active 
cells and almost any degree of cold. 
The dried cells and spores float in the air as dust and so accomplish 
a dispersal of the organism. Doubtless most of them never again 
meet suitable environment and so sooner or later perish. But some 
villi fall into favorable conditions and be able to multiply enormously 
again, and so the species is continued. 
The general method of reproduction in Saccharomyces is that of 
gemmation or budding. A small protuberance of the cell wall com- 
mences to form on the parent-cell. This grows larger and a portion 
of the cytoplasm and nuclear material pass into it. Eventually a 
daughter-bud, which may assume the size of the parent-cell, is formed. 
This generally adheres to the parent-cell and produces one or more 
granddaughter-buds which in turn may produce great-granddaugh- 
ter-buds before separation from the parent-cell takes place. 
