ermentation is, according to Kuntze, the result of the
action of various organisms. During the initial stage butyric acid
fermentation takes place, but is prevented from becoming predominant by
the action of the keffir yeast. Simultaneously a true lactic acid
fermentation proceeds and eventually gives place to a subsequent
secondary production of butyric acid. Finally, then, we have a certain
amount of unison in the results obtained by Freudenreich, Essaulow,
Nikolaiewa, and Kuntze. These show that, for the production of a
characteristic keffir, specific organisms are not essential, provided
always that those used possess, either individually or collectively, the
essential capacity of acidifying, coagulating, and fermenting the milk.
For the growth of normal grains the presence of a matrix-forming
organism, such as _Bacillus keffir_, is indispensable.

[Illustration: FIG. 12--_Streptococcus lacticus_
(Grotenfeldt) growing on lactose-agar, stained by Gram's
method. ( X 900 diams.)]

_Diseases of Keffir Grains._--According to the age and the previous
treatment to which keffir grains have been subjected, the vitality of
one or more of the organisms constituting the grain may have been
impaired. The results of Freudenreich have shown that _Saccharomyces
keffir_ and _Streptococcus a_ are unable to withstand desiccation for
more than a few days, and this is sufficient to account for the frequent
failures to obtain normal keffir from the grain. Further, grains succumb
to a mucilaginous disease; the cavities become filled with a slimy
fluid, and the grains are covered with mucilaginous matter. They lose
their elasticity and become brittle or mealy, but large grains appear to
be more subject to this fault than do the small ones. Such grains
should be disinfected by immersion for a short time in two per cent.
salicylic acid solution, followed by drying in the sun, whereby they are
completely regenerated.

Another disease consists in the predominance of certain butyric acid
bacteria which impart an unpleasant rancid taste to the keffir
(Podowyssozki). This is generally attributed to the use of rich milk, or
too high a temperature during preparation.

_Koumiss._--Another product of the combined action of lactic acid and
alcohol-producing organisms is called koumiss, kumys, milk-wine, lac
fermentation, or vinum lactis. In the steppes of Southern Russia and
Asia, as we have seen,[59] it is prepared chiefly from mares' milk,