th of period to which this
subsequent fermentation is allowed to proceed, the resultant keffir is
more or less acid and gaseous. The grains may again be used for starting
a fresh portion of milk, and a regular supply obtained in this manner.
Well-fermented forty-eight-hours-old keffir should be an effervescent
beverage with prickling and acid taste and a consistency and smell
similar to sour cream. Large, persistent bubbles should form on the
surface of the liquid and the casein be present as an extremely fine
flocculent precipitate which remains suspended for a considerable time.

From the third day there ensues a gradual peptonisation of the casein.
If the temperature at which the secondary fermentation has occurred
should be higher than 72 deg. F., or if the milk has not been sufficiently
agitated, then the casein will be present in the form of porous small
flakes, which on shaking form a fine emulsion.

The chemical changes undergone by the milk during the preparation of
keffir are confined almost exclusively to the milk sugar. As already
stated, a slight peptonisation occurs in old samples, but this depends
very largely upon the method of preparation and purity of the culture.
Hammersten[49] and Essaulow[50] show, however, that this is not a
concomitant of normal fermentation. According to Hammersten, normal
keffir contains--

Per cent.
Water 88.26
Fat 3.35
Casein 2.98
Lactalbumen 0.28
Peptones 0.05
Milk sugar 2.78
Lactic acid 0.81
Alcohol 0.70
Ash 0.79

In no case should the acid be higher than 1.0 per cent., and the alcohol
more than 0.75 per cent.

_Biology of the Keffir Grain._--The first communication on the biology
of the keffir grain seems to have been made by Kern.[51] He regarded the
grain as a zoogloea composed of bacilli and yeasts, the latter being
regarded as the ordinary beer yeast (_Saccharomyces cerevisseae_), while
to the former he gave the name of _Dispora caucasica_. As the name
indicates, this bacillus possesses two polar spores, and germination of
these proceeded in the same manner as with _Bac. subtilis_. As, however,
pure cultures of the organisms were not made, and the descriptions and
illustrations made by Kern fail to show any distinctive characteristi