STUDIES ON FERMENTATION. 279 



confounded completely with ordinary alcoholic fermentation, 

 yielding the same products and in the same proportions. It 

 is through the misuse of words that the fermentation of fruits 

 has been termed alcoholic, in a way which has misled many 

 persons.* In this fermentation, neither alcohol nor carbonic 

 acid gas exists in those proportions in which they are found in 

 fermentations produced by yeast ; and although we may deter- 

 mine in it the presence of succinic acid, glycerine, and a small 

 quantity of volatile acids,t the relative proportions of these 

 substances will be different from what they are in the case of 

 alcoholic fermentation. 



§ III. — Eeply to certain Critical Observations of the 

 German Naturalists, Oscar Brefeld and Moritz 

 Traube. 



The essential point of the theory of fermentation, which 

 we have been concerned in proving in preceding paragraphs, 

 may be briefly put in the statement that ferments, pro- 

 perly so called, constitute a class of beings possessing the 

 faculty of living out of contact with free oxygen ; or, more 

 concisely still, we may say, fermentation is a result of life 

 without air. 



If our affirmation were inexact, if ferment-cells did require 

 for their growth or for their increase in number or weight, as 



* See, for example, the communications of MM. Colin and Poggiale, 

 aud the discussion on them, in the Bulletin de V Academic de Medicine, 

 March 2nd, 9th, and 30th, and February 16th and 23rd, 1875. 



f We have elsewhere determined the formation of minute quantities of 

 volatile acids in alcoholic fermentation. M. Bechamp, who studied these, 

 lecognized several belonging to the series of fatty acids, acetic acid, 

 butyric acid, &c. "The presence of succinic acid is not accidental, but 

 constant ; if we put aside volatile acids that form in quantities which we 

 may call infinitely small, we may say that succinic acid is the only 

 normal acid of alcoholic fermentation." Pasteur, Comptes revdus de 

 V Academic, t. slvii. p. 224, lRo8 



