THE BACTERIA IN DIFFERENT MEDIA. 139 
of our knowledge. I will not then seek to clas- 
sity 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 : — 
Ce. = = CAH + HO. 
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 
