36 
PRINCIPLES OF BACTERIOLOGY 
the fermentation of carbohydrates (sugars and starches) 
and in the splitting of fats and proteins. 
For our entire knowledge of fermentation we are 
indebted to the genius of Pasteur who was first to 
explain to us that the fermentation (as well as the 
splitting of proteins) is due to ferments or enzymes 
(from Latin and Greek respectively, meaning “lea¬ 
ven”). These are substances produced by a living 
cell, which produce about a chemical change without 
entering into the reaction themselves. The ferment is 
not attached to the end products of the reaction, and 
is not appreciably diminished during the reaction; in 
this way the bacterial ferments are like the chemical 
agents known as katalyzers—e. g., dilute acids, which 
bring about various chemical reactions and yet do not 
enter them themselves, as, for example, when a solu¬ 
tion of cane sugar brought into contact with dilute 
solution of sulphuric acid results in the formation of 
two single sugars in place of a double sugar: 
C 12 H 22 0 n + H 2 0 + H 2 S0 4 — C 6 H 12 0 6 + C 6 H 12 0 6 + H 2 S0 4 . 
Cane sugar water sulphuric acid = grape sugar fruit sugar sulphuric acid 
The proper definition for ferments or enzymes is, 
therefore, “a substance which hastens a chemical re¬ 
action without itself taking part in it.” The best 
conditions for the ferment action are the presence of 
moisture, a weakly acid or alkaline reaction, and a 
temperature ranging from 35° to 45° C. 
The presence of protein-splitting, or proteolytic, as they 
are called, ferments is shown by the power of bacteria to 
liquefy gelatin, fibrin or coagulated blood serum. Among 
the important products of bacterial proteolysis are the 
ptomaines (from Greek ptoma meaning a dead body) 
which are highly poisonous and responsible for ptomaine 
poisoning. 
