142 PHYSIOLOGY OF THE BACTERIA. 
Ammoniacal Fermentation of Urine. — When 
urine is freely exposed to the air, we perceive at 
the end of a short time that it has become strongly 
ammoniacal. The urea is transformed into carbon- 
ate of ammonia by the addition of water : — 
CO(NH2)? + H20 = CO? + 2NH’. 
Miiller suspected that the deposit of altered 
urine, of which Jacquemart had already recognized 
the particular activity, was an organized ferment, 
but this was only an induction drawn from the 
analogy with beer yeast. Pasteur showed that 
this sediment is formed of a mass of spherical 
globules, united in chaplets, which he considers the 
agent of ammoniacal fermentation. These glob- 
ules are Micrococcus urew, Cohn, which we have 
already described (page 795). 
This bacterium lives in the interior of the liquid, 
and not on the surface like the MWycoderma acett. 
Acidity is an obstacle to its development; alkalin- 
ity, on the contrary, favors it within certain limits. 
Van Tieghem has even seen the fermentation con- 
tinue until the liquid contained thirteen per cent 
of carbonate of ammonia. 
What is the mechanism of this fermentation ? 
M. Musculus has shown that we may obtain 
from altered urine a soluble ferment upon adding 
to it highly-concentrated alcohol: a precipitate is 
formed, which may be filtered and dried. This 
precipitate, not at all organized, transforms urea 
into carbonate of ammonia. A temperature of 
80° (176° Fah.) destroys it. This diastase appears, 
