64 BACTERIOLOGY. 
This may be accomplished by the addition of disinfect- 
ants—carbolic acid, chloroform, ether, ete.—to the cul- 
tures or by filtration. Ferments, like albuminoids, 
are non-dialyzable. They withstand dry heat, but are 
destroyed in watery solutions by a temperature of over 
70° C. They are injured by acids, especially the 
inorganic ones, but are resistant to all alkalies, All 
fermentation has for its object the acquisition by the 
organism of a store of energy. This is accomplished 
in either of the ways above mentioned. The simplest 
and commonest example of decomposing fermentation 
produced by an enzyme is that of sugar : 
C,H,0,; = 26,H,0 + 200, 
Grape-sugar. ~ 2 Alcohol, 2 Carbon dioxide. 
or, 
CH 1:05 or 2C,H,03 
Grape-sugar. 2 Milk-sugar. 
or, : 
CyHi,0, = 3C,H,0, 
Grape-sugar. 3 Acetic acid. 
Bacteria which develop in the absence of oxygen are 
especially in need of this source of oxygen. Anaérobic 
bacteria, for this reason, have the power of decomposing 
sugar, while many facultative anaérobes are only capable 
of producing fermentation when oxygen is excluded. 
Opposite to this, and far less common, is oxidizing 
fermentation, as in the production of acetic acid from 
alcohol. Here the energy is acquired not by the de- 
composition but by the oxidation of the alcohol. 
The proteolytic or peptonizing ferments which are 
somewhat analogous to pepsin and trypsin—being capa- 
ble of changing albuminous bodies into soluble and 
diffusible substances—are very widely distributed. 
The liquefaction of gelatin, which is chemically allied 
