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32 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

F, Animoviacal Fernuntation.

Various bacteria, Aseococcus Billrothii, Micrococcus urese,
Bacillus ureae, etc., occasion a fermentation of urea leading to the
formation of carbonate of ammonia, and imparting an intensely
alkaline reaction to the solution. W. Leube and E. Greser^
obtained pure cultures of four diiferent bacteria which have the
power to decompose urea. Two of them, a small bacillus
(Bacterium urepe) and a coccus (Micrococcus ure?e), showed
intense urea-decomposing properties. The other two possessed
this property in a less marked degree. Lungsarcina also effected
an intense decomposition of urea,

G. Xifrijication and DenUriJicafwii.
Finally, certain processes of oxidation and reduction which
take place in the soil have been found to be due to the presence
of micro-organisms, and must consequently be classed under fer-
mentations. Schlosing and Miintz^^ established this fact for the
case of natural nitrification, which, according to their experi-
ments, must be regarded as a process of fermentation, resulting
from the action of a specific micro-organism. In their experi-
ments they used filtered and sterilized drainage-water (I'eau
d'egout), or weak alkaline solutions containing mineral sub-
stances, a salt of ammonia, and organic matter. When these
solutions were sterilized, infected with soil and exposed to the air,
a nitrate-forming fermentation ensued, which was occasioned by
very small oblong microbes (ferment nitrique). Continuous
exclusion of air destroyed the ferment nitrique ; it occurs very
extensively, but was not found in the atmosphere.
The conditions for the consummation of this process are (1)
access of oxygen, (2) a certain degree of humidity, (3) weak
alkalinity, and (4) the presence of organic matter. Below 5° C.
nitrification proceeds very slowly ; at a higher temperature the
intensity of the fermentation increases, until 37" C. is reached,
which represents the maximum. At a still higher temperature
it decreases rapidly, and at 50° C. (!) yields bat minute quanti-
ties of nitrates.
On the other hand, Gayon and Dupetit^*^ found four diflierent