TYPES OF BACIERIA FOUND IN MILK I71I 
readily undergo an alcoholic fermentation, but milk sugar does 
not easily make this change. It may be converted into lactic 
acid, but not readily into carbon dioxid and alcohol. Hence an 
alcoholic fermentation of milk is not a normal phenomenon, 
although it may be produced by the addition of a little cane-sugar 
to the milk. The possibility of making milk undergo an alco- 
holic fermentation by the addition of yeasts is made use of in the 
manufacture of kummys. This beverage was originally prepared 
by the Arabs from mare’s milk, which will normally undergo an 
alcoholic fermentation; but now an imitation product is widely 
Fic. 38.—A large-sized kefir grain and the three species of bacteria of 
which it is composed (Freudenreich). 
made and used, prepared from cow’s milk. A small quantity of 
sugar is added to milk and some common baker’s yeast. An 
alcoholic fermentation soon begins, and the fermented product 
is kummys. Various modifications of this general process are 
adopted by different makers, for kummys has become a commer- 
cial article. 
In addition to these there are several other types of beverages 
made from milk in common use among different nations, in the 
production of which alcohol is formed. One, known as kefir, 
has long been used in the Caucasus mountains. The fermentation 
is brought about by adding to the milk what are known as kefir 
grains (Fig. 38). These are hard nodules of various sizes which 
