148 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



case ultimate products, such as C0 2 and other gases, result. 

 Incidentally, as it were, more of the medium has to be broken 

 up than actually suffices for the food of the organism, and we 

 thus get the normal products of fermentation. The course of 

 reaction, therefore, in every case depends on several factors, viz. : 



1. The nature and molecular constitution of the ferment- 

 able substance, whether an alcohol, aldehyde or ketone, etc. 



2. Whether any other food supply is present, thus, e.g., 

 the character of the decomposition of a sugar has been found 

 to vary according to the presence or otherwise of peptone in 

 the nutrient mixture. 



3. The species and state of growth of the organism ; for 

 instance, results will vary according as the culture is or is not 

 of recent growth, or according to whether it comes from 

 strains which have been transplanted from time to time in the 

 laboratory. 



A complete account of all the oxidation changes of the 

 type under consideration, and of the bacteria concerned 

 therein, would lead too far and would be of doubtful utility, 

 inasmuch as many of them have not been worked out in 

 detail. Keference will be made in the first place to three 

 fermentations of technical importance, and afterwards some 

 account will be given of the detailed work in the case of 

 specific organisms which will serve to illustrate the method 

 of research used in this class of inquiry. 



The Oxidation of Alcohol to Acetic Acid. The simple 

 equation expressing this reaction is as follows : 



CH 3 CH 2 OH + 2 = CH 3 C0 2 H + H 2 



In reality, for reasons mentioned above, the bacterial 

 oxidation of alcohol is by no means capable of so simple an 

 expression. 



It is well known, of course, that alcoholic liquids such as 

 wine and beer, on exposure to air, gradually become sour. 



