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 

 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 of young 

 children annually. 



