124 ATLAS OF BACTERIOLOGY. 



On account of the practical (and diagnostic) im- 

 portance of the fermenting power we must here give 

 a precise definition of this process. The term fermen- 

 tation is used in literature in various senses. 



1. Some writers call every typical decomposition 

 produced by bacteria a fermentation, and speak, for 

 example, of the putrid fermentation of albuminoids. 



2. Others confine the term fermentation to proc- 

 esses which are attended with the visible develop- 

 ment of bubbles of gas. According to this definition 

 the conversion of nitric acid into nitrogen is a fer- 

 mentation as well as the fermentation of milk sugar 

 by bacterium acidi lactici. 



3. Still others use the term only in cases of decom- 

 position of hydrocarbons with or without the forma- 

 tion of gas. 



It seems to me that the term fermentation is always 

 in place when it can be shown that an organism, in 

 addition to or instead of its other metabolic products, 

 forms one or a few special metabolic products in an 

 unusual amount metabolic products which are al- 

 most always derived from the merely superficial 

 splitting up of a bacterial nutrient which is easily split 

 up. Oxidative fermentation is rarer. A necessary 

 condition of fermentation is the presence of a definite 

 nutrient matter which the bacteria attack with special 

 ease, often discarding substances which are less acces- 

 sible but which they decompose in the absence of 

 the fermenting substance. 



Every fermentation is intended to carry a supply 

 of energy to the fermenting organism, In the fer- 

 mentation which splits up organic material, this is 

 due to the fact that the complicated, fermentible 



