64 BACTERIOLOGY. 



This may be accomplished by the addition of disinfect- 

 ants carbolic acid, chloroform, ether, etc. 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 

 morganic 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 6 H 12 O 6 = 2C 2 H 6 O + 2CO 2 

 Grape-sugar. 2 Alcohol. 2 Carbon dioxide. 



or, 



C 6 H 12 6 = 2C 3 H 6 3 

 Grape-sugar. 2 Milk-sugar. 



or, 



CVH 12 O 6 = 3C 2 H 4 O 2 

 Grape-sugar. 3 Acetic acid. 



Bacteria which develop in the absence of oxygen are 

 especially in need of this source of oxygen. Anaerobic 

 bacteria, for this reason, have the power of decomposing 

 sugar, while many facultative anaerobes 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 



