TYPES OF FERMENTATION AND DECAY 29 
at low temperatures and also at high temperatures, and occurring 
with vigor within limits of temperature not far apart. Most of 
them occur most vigorously at temperatures between 80° and 
100°F, 
3. They are all produced by the stimulating action of some 
special body, present in the fermenting material in a quantity 
which is very small, considering the great changes produced. 
4. These bodies (ferments) are all rendered inert or destroyed 
by heat; a boiling temperature commonly destroys them so com- 
pletely that they are unable to renew their action even after cool- 
ing. Low temperatures simply check their activity, which they 
are able to renew if warmed again. 
5. Their action is completely stopped by an accumulation of 
the products of their own activity. 
If we ask what is the body producing the action (the ferment), 
we find that the first and last of the types described differ from the 
second in one radical point. Whereas the alcoholic fermentation 
and putrefaction are directly produced by living germs, either 
yeasts or bacte1ia, the amyolytic fermentation is not produced by 
a living organism, but by some xon-living substance secreted from a 
living being. ‘To explain this a brief account is required of the 
development of our knowledge of fermentations in general. 
Fermentations have been known for centuries. Even in an- 
cient Egypt the production of alcohol was familiar. Every savage 
tribe has its own method of obtaining alcohol by the fermenting 
of fruit juices, and the process is one of the most widely-known 
changes in nature. For a time it was regarded as a putrefying 
process, the yeasts found in the fermented material being looked 
upon as an impurity which was separated from the rest. The 
chemical nature of alcoholic fermentation was determined early 
in the nineteenth century, but its relation to the yeasts was not 
determined until 1837, when Schwann demonstrated that fermen- 
tation would not occur except under the influence of yeasts. The 
conclusion that it was the result of the growth of yeasts was 
