64 ACTIVITIES OF BACTERIA. 



II. The Chemical Activity of Bacterial Metabolism. 



As with ferment production, so also most other chem= 

 ical activities of bacteria depend in great measure upon 

 nutrient media. This is most striking when one observes 

 the growth of several varieties of bacteria upon albuminous 

 nutrient media, at one time without sugar and again 

 containing sugar. While in the first case, except for the 

 formation of pigments and some odoriferous substances, 

 there is scarcely any appreciable metabolism, in the second 

 case there often occur striking distinguishing changes char- 

 acterized by the development of gas and active production 

 of acid. Thus the organism produces "fermentation" 

 in the medium containing sugar; in the other, none. 



Because of the practical (and diagnostic) importance of 

 the ability to produce fermentation, there must first be 

 given a precise definition of the process. 



The expression * fermentation " is employed in the 

 literature with the most varying meanings. 



1. Many authors call every typical decomposition caused 

 by bacteria "fermentation," and speak, for example, of 

 the putrid fermentation of albuminous bodies. 



2. Others limit the word "fermentation" to processes 

 which are accompanied by evident gas bubbles. According 

 to this definition, the liberation of nitrogen from saltpeter 

 is as much fermentation as the breaking up of milk-sugar 

 by the Bact. acidi lactici. 



" 8. Still others only speak of fermentation when there 

 occurs a breaking up of carbohydrates, with or without 

 gas production. 



To me the expression " fermentation " is only applicable 

 when it is proved that an organism produces, along with or in- 

 stead of its other metabolic products, one or more special meta- 

 bolic product in striking amount; products of metabolism 

 which almost always arise from the merely superficial splitting 

 up of an easily decomposed bacterial nutrient material (split- 

 ting fermentation). Oxidation fermentation is more rare 

 (compare below). The essential for fermentation is al- 

 ways the presence of a special nutrient material, which the 

 fungus appropriates very easily, often rejecting materials more 



