similar foods, owe their peculiar properties primarily to
the presence of _Bacillus bulgaricus_ (type A, White and
Avery), and only in a lesser degree to the yeasts and
lactic streptococci.]

_Matzoon._--This is a drink used largely in Western Asia, and is similar
in character to keffir, but has a peculiar taste which distinguishes it
from all other fermented milks. According to Weigmann,[66] it is
prepared from buffaloes', goats', or cows' milk, and is used partly as a
means of souring milk for butter-making and also as a lactic food, eaten
with spoons. In the same way buttermilk produced from milk which has
been previously ripened by matzoon is used as a beverage. Finally, the
coagulum (_than_) of such buttermilk is strained off, and, after being
pressed, is mixed with meal and dried by exposure to the sun's rays. The
preparation of matzoon is in many respects very similar to that of
keffir and koumiss, but differs by inducing a comparatively weak alcohol
fermentation. In common, too, with yoghourt, the prevailing temperature
is much higher than is required for keffir and koumiss.

In regard to the biology of matzoon, the occurrence of various organisms
has been recorded. Emmerling[67] isolated, in addition to a yellow
pigment-forming organism, _Bacillus subtilis_, _Bacillus lactis acidi_,
and several fungi, a small micrococcus capable of hydrolysing milk- and
cane-sugar. The organism produces and without gas formation, or
peptonisation of the medium. Of the nine yeasts isolated from matzoon by
Lindner[68] and Kalantharianz,[69] three were able to ferment milk sugar
without previous hydrolysis, while two others, by the simultaneous
production of lactic acid and fruit esters, gave to the matzoon its
characteristic taste and aroma.

_Yoghourt and Soured Milk._--Yoghourt is another fermented milk, and is
related to the matzoon of Armenia, the gioddu of Sardinia, and the leben
of Egypt. After a preceding boiling and reduction of the volume of the
milk, inoculation of the mass is made by the addition of a small
quantity of old culture, and it is then allowed to sour at a
comparatively high temperature. A moderately compact, jelly-like
coagulum is thus formed, while keffir and koumiss possess a liquid
consistency. The fermentation necessary for the two latter products only
proceeds, too, at a much lower temperature, at which yeasts play an
important part. According to Guerbet, yoghourt incubated for ten hours
at