144 PHYSIOLOGY OF THE BACTERIA. 
this subject. Let us, however, mention before 
closing an interesting work by MM. Cazeneuve 
and Livon, in which are reported some experiments 
which prove that urine never ferments in a healthy 
bladder. 
Lactic, Butyric, and Viscous Fermentations of 
Sugars. — Saccharine liquids, left to themselves, 
-are susceptible of divers fermentations, which may 
occur separately or simultaneously. Those which 
have been best studied are three, — the lactic, the 
butyric, and the viscous fermentations. We will 
describe them successively. 
1. Lactic Fermentation.— Under the probable 
influence of a bacterium ( ferment lactique of Pas- 
teur) glucose and the substances susceptible of 
furnishing it, such as mannite, malic acid, etc., are 
transformed into lactic acid. 
From a chemical point of view, there is in this 
nothing more than a molecular change, lactic acid 
having the same composition as glucose. 
Taken in mass, the lactic ferment resembles 
beer-yeast; its consistence is, however, a little more 
viscous, and its color more gray. But under the 
microscope, the aspect is very different, as we have 
seen in describing Bacterwum lineola. 
An interesting point concerning this fermenta- 
tion is the action of acids upon the bacteria which 
produce it (presumably). As soon as the medium 
becomes acid, even by the lactic acid produced, the 
transformation is arrested. It resumes its course, 
if chalk or carbonate of soda is added to the 
liquid. 
