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26 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

A second experiment showed as chief product capronic acid,
and as by-products hut^'ric and lactic acids. In other cases of
glycerine fermentation Fitz discovered traces of acetic acid, with
butyl alcohol as principal product. The Bacillus butyricus fer-
mented glycerine, so that butyric acid, as well as acetic, capronic,
and lactic acids, were formed. Different experiments with ery-
thrite 3'ielded alcohol, butyric, acetic, also traces of formic and
succinic acids, Mannite yielded butyl and ethyl alcohol, butyric
and succinic acids, with a variable quantity of capronic, acetic,
lactic, and formic acids. Dulcite gave many volatile and some
non-volatile acids ; quercite gave normal Ijutyric acid, etc.
Fitz probably employed impure cultures in all his experi-
ments, which would explain the large number of products of
fermentation. It is not to be supposed that these fermentations
play an important part in the mouth, as the necessary nutrients
are not present in sufficient quantities, or in part are altogether
wanting.

C. Fermentation of Fats, Fatty Acids, and Oxijacids.
Fats exposed to the air soon become rancid, as is well known,,
and give off a more or less strongly marked odor of fatty acids.
This change is due to a decomposition of the fats into glycerine
and fatty acid, under the action of micro-organisms.
The following tatty and oxyacids and their salts are also fer-
mentable : formic and acetic acids, lactic acid (oxypropionic acid),
glycerinic acid, malic (oxysuccinic) acid, tartaric (dioxysuccinic
acid, citric (oxytricarballylic) acid.
Formate of lime yields CaCOg, CO2, and H;
Acetate of lime yields CaCOs, COg, and CH^.
According to Fitz, lactate of lime undergoes four different
fermentations. In the first are formed propionic acid, and as
by-j)roducts, acetic and succinic acids and alcohol ; in the second,,
propionic and. valeric acids; in the third, butyric and propionic
acids; in the fourth, butj-ric acid, with ethyl and butylic alcohol
as by-products.
Glycerate of lime produces tartrate of lime, with succinic acid
and ethyl alcohol as by-products ; according to Fitz, also acetic
acid and traces of formic and succinic acids.