d into free fatty acids, which ultimately unite
with the ammonia produced by the breaking up of the albuminoids. The
main fermentation of milk is a special kind which of late years has been
much studied, and is known as _lactic fermentation_. Accompanying lactic
fermentation there is nearly always a weak butyric and a weak alcoholic
fermentation."

One of the organisms causing _Butyric Acid Fermentation_ is a bacillus 3
to 10 mu in length, and about 1 mu in breadth. It has power of movement, and
when cultivated in gelatine, liquefies the gelatine, forming a scum on
the surface. When the bacillus is sown into sterile milk, the following,
according to Hueppe, are the changes:

"If the milk thus infected is incubated, on the second day a clear,
slightly yellow fluid is seen under the layer of cream; this fluid
increases from day to day, so that gradually a column of fluid is
formed which is quite clear above, but below is turbid; the casein, at
first thrown down in a firm coagulum, in the course of eight days begins
to be attacked, and by the end of two or three weeks most of it is
dissolved. The filtered fluid gives the biuret reaction; it contains
leucin, tyrosin, and ammonia; hence it is clear that the ferment acts to
some extent as a digestive of albumen. In advanced butyric acid
fermentation, the fluid is most offensive, and may have an alkaline
reaction."

Lactic acid was first isolated by Scheele in 1780 from soured milk, but
its exact constitution was not determined until later by Liebig,
Mitscherlich, Gay-Lussac, and Pelouze: "It is widely distributed in
nature, occurring in the sap of the vine and in most fermented liquids,
especially in soured milk; it is not, however, present in fresh
milk."[15]

In all the Eastern preparations referred to, the lactic fermentation is
produced, followed by alcoholic fermentation, which is due to the slow
decomposition of the milk sugar, the vinous fermentation being most
readily set up in milks which contain a larger relative proportion of
milk sugar and water, such as the milk derived from the mare, the sheep,
and the camel. As these fermented milks have different characteristics,
it is necessary to the thorough understanding of the process of
manufacture at the present day, to examine them in some detail.

_Koumiss._--The greatest of all the fermented milks is koumiss, and it
has been celebrated from the most ancient times until the present day,
as being the principal fo