y peptonised.[26] Keffir becomes slightly effervescent in
twenty-four hours, and in that time develops a small quantity of
alcohol, but after three days the amount of alcohol and lactic acid
is much increased.[27] It has been determined that the fermentation of
the milk is due to _Saccharomyces kefir_, and that the _Lactobacillus
Caucasicus_ does not take any part in the fermentation, a fact which
seems to be supported by the capacity of ordinary keffir for starting
the fermentation in fresh milk in the same manner as the keffir grains.
The use of this beverage seems to be universal throughout the Caucasus,
and travellers in these regions have frequently referred to it. Thus
Freshfield[28] states in one part of his book of travels as follows:

"The pig-faced peasant against whom we had at first sight conceived such
an unjust prejudice turned out a capital fellow. He brought us not only
fresh milk, but a peculiar species of liquor, something between
public-house beer and sour cider, for which we expressed the greatest
admiration, taking care at the same time privately to empty out the
vessel containing it, on the first opportunity." And again:

"The hospitable shepherds regaled us, not only with the inevitable and
universal airam or sour milk--if a man cannot reconcile himself to sour
milk, he is not fit for the Caucasus--but with a local delicacy that
has lately been brought to the knowledge of Europe--kefir. This may best
be described as 'effervescing milk.' It is obtained by putting into the
liquid some yellow grains, parts of a mushroom which contains a bacillus
known to science as _Dispora caucasia_. The action of the grains is to
decompose the sugar in the milk, and to produce carbonic acid and
alcohol. The grains multiply indefinitely in the milk; when dried they
can be preserved and kept for future use; its results on the digestion
are frequently unsatisfactory, as one of my companions learnt to his
cost."

"It has been supposed," says Metchnikoff, "that the chief merit of
kephir was that it was more easy to digest than milk, as some of its
casein is dissolved in the process of fermentation. Kephir, in fact, was
supposed to be partly digested milk. This view has not been confirmed.
Professor Hayem thinks that the good effects of kephir are due to the
presence of alcoholic acid, which replaces the acid of the stomach and
has an antiseptic effect. The experiments of M. Rovigh, which I speak of
in _The Nature of M