384 
Micro-organisms and their Action 
fermentation, the first condition is that the milk-sugar be 
converted into a sugar of a more simple composition — a trans- 
formation which is effected by the bacillus of lactic fermentation, 
and perhaps also by lactic acid. We find, therefore, that alcoholic 
fermentation does not take place in sweet milk, and even after 
the latter has turned sour it is not possible to easily produce 
alcoholic fermentation by the addition of common yeast, a 
special ferment being necessary. During the last few years 
such a ferment has become known under the name of " Kephir " 
ferment. It was discovered in the Caucasus, where it appears it 
has been used from time immemorial for the manufacture of a 
native beverage. The ferment in the form in which it is used 
consists of small lumps differing in size from that of a pea to 
that of a hazel-nut, irregularly shaped and somewhat resembling 
cauliflower, of a dirty grey or yellowish-brown colour. When 
examined microscopically these lumps (or " grains " as they are 
called), are found to consist of three different species of micro- 
organisms ; first, the bacillus of lactic fermentation ; second, a 
larger bacillus ; and third, a cultivated yeast. 
The yeast cells are apparently not distinguishable from the 
common beer yeast. Like the latter, they do not form spores, 
but multiply by budding only. With regard to the larger bacillus, 
new cells are formed by means of divisions taking place. The 
newly formed cells either separate, or remain connected, forming 
long threads. There are also found aggregations of cells, united 
by a sticky, slimy mass ; single cells are frequently seen moving 
about. The formation of spores invariably takes place, so that 
two spores are formed, one at each end of the cell. 
There can be no doubt as to the part which the bacillus of 
lactic fermentation plays ; it decomposes part of the milk sugar 
into lactic acid, and carbonic acid. Another portion of the sugar 
gets hydrated under the influence of the same organisms, and is 
then decomposed by the second micro-organisms present, the 
veast cells, alcohol, and carbonic acid being formed as the result 
of their action. Although one must suppose that, besides alcohol 
and carbonic acid, traces of other bodies, such as glycerine, 
fusel oil, and succinic acid, are formed as bye-products, as is the 
case when alcoholic fermentation takes place in sugar solutions, 
there is no evidence to show that the presence of these bye-pro- 
ducts has ever been proved in fermented milk. A further 
change which takes place consists of the partial peptonization 
of the casein and albumen, and this must be assigned to the 
action of the larger bacillus. 
The presence of the three forms of micro-organisms in com- 
bination appears to be necessary to effect the changes described. 
The result of the action of Kephir grains upon milk is a beverage 
