172 BACTERIA IN MILE 
have the power of starting an alcoholic fermentation in ordinary 
cow’s milk. The origin of these kefir grains is unknown. To- 
day they are handed from person to person, taken from the fer- 
mented milk and dried to be used again. During the fermenta- 
tion in the milk they increase in size and new grains may be ob- 
tained from fragments of the old ones. In Egypt the people 
use a fermented milk called leben. Another, called mazoon, is 
common in Armenia. The Turks have one they call yoghourt, 
and in Sardinia still another is found with the name of goiddu. 
In all these cases the beverage is prepared by the use of ferments 
that the people keep on hand, whose original sources are unknown. 
These ferments, so far as they have been studied, prove to be 
based upon the combined action of yeasts and bacteria. Very 
likely the bacteria change the milk-sugar into a fermentable form 
and at the same time sour the product. The yeast is probably 
responsible in all cases for the alcoholic fermentation proper, 
although in some the milk souring by the bacteria is the primary 
feature, while the action of the yeasts is secondary and is not 
regarded by some as at all essential to the product. In several of 
these products the type of lactic acid organism mentioned under 
the name of B. bulgaricus is present. The beverages are generally 
regarded as more digestible than ordinary milk. 
GROWTH OF BACTERIA IN MILK 
The number of bacteria that may be in any sample of milk is, 
in the first place, dependent upon the number and variety that 
get into the milk during and after the milking. But the original 
contamination is only a small factor in determining their number 
at any subsequent time. Milk furnishes excellent food for bac- 
teria, and when drawn from the cow it is warm. Hence a rapid 
multiplication of bacteria begins; but although the milk furnishes 
such an excellent medium for them, they do not begin to multiply 
at once. For a few hours their number remains the same or even 
decreases. ‘There seems to be something in fresh milk that injures 
