14 
HOUSEHOLD BACTERIOLOGY . 
or less dusty. Among these hundreds of forms are 
some that like the sugar of the milk as food. While 
feeding upon this, they change a part of it into acid- 
lactic acid. When this acid reaches *a certain amount, 
it coagulates the casein of the milk. 
Production The cleaner the milk, the fewer of these lactic acid 
.actic Acid producing plants will be present and the longer the 
milk will keep sweet. Cold retards their growth. 
Milk should then be cooled as quickly as possible 
after being drawn from the cow, and should be kept 
in a cold place at all times. 
Milk is a most favorable culture ground for bac¬ 
teria because it has some of all classes of food ele¬ 
ments, being what is known as a perfect food. Its 
opaqueness hides much of the solid dirt which not 
only seeds it with bacteria but adds certain soluble 
matters. Too often the dirty character of the milk is 
known only by sight of the actual dirt at the bottom 
of the empty glass. 
The possibilities in the way of clean milk, which 
means safe milk, were forcibly illustrated by exhibits 
from some American “model dairies” at the Paris Ex¬ 
position in 1904. Milk and cream in a perfectly fresh 
condition were shown after a journey of ten days; the 
only treatment being extreme cleanliness in milking, sta¬ 
ble, receptacle, etc., and cold. A glass of ordinary, un¬ 
clean milk contains millions of bacteria, which al¬ 
though harmless to a vigorous adult are the cause, di¬ 
rect or indirect, of the death of thousands cf young 
children annually. 
