THE BACTERIA IN DIFFERENT MEDIA. 139 



of our knowledge. I will not then seek to clas- 

 sify them, but will content myself with describ- 

 ing them successively, commencing with the best 

 known. I shall only speak of the fermentations 

 caused by the development of bacteria, leaving, 

 consequently, the fermentation which has been 

 best studied, the alcoholic. I adopt the follow- 

 ing order : 



1. Acetic fermentation of alcohol. 



2. Ammoniacal fermentation of urine. 



3. Lactic, viscous, and butyric fermentations of sugar. 



4. Putrefaction, or nitrification. 



Acetic fermentation. The transformation of 

 wine into vinegar is a phenomenon long known 

 and utilized. From a chemical point of view, this 

 transformation is due to oxydation of the alcohol. 

 The following formula represents this reaction : 



C 2 H 6 O + O 2 = C 2 H 4 O 2 + H 2 0. 



The agent of this oxydation is a micro-organism 

 called Mycoderma aceti. It belongs to the group 

 of the microbacteria, and we have already given 

 the botanical description of it (page 83) ; but its 

 development presents some interesting peculiar- 

 ities which we think it proper to indicate in the 

 language of M. Duclaux : 



" These little beings reproduce themselves with 

 such rapidity that by placing an imperceptible germ 

 upon the surface of a liquid contained in a vat 

 having a surface of one square metre, we may 

 see it covered, in from twenty-four to forty-eight 

 hours, with a uniform velvety veil. If we suppose 



