Contamination of Milk. * 55 



If the temperature is immediately lowered to 50 F., or 

 lower, actual cell development is greatly retarded, and 

 the rate of souring, and other fermentative changes 

 thereby diminished. In this country ice is liberally 

 used in accomplishing this result. In Europe, the use 

 of ice is much less common. The employment of such 



PROGENY OF A 

 SINGLE GERM e 

 IN TWELVE HOURS 



FIG. 16. EFFECT OF COOLING MILK. 



artificial means of refrigeration makes possible the ship- 

 ment of milk for long distances by rail. New York city 

 now receives milk that is produced in Canada and north- 

 eastern Ohio. 



Aeration of milk. The custom has been extensively 

 recommended of subjecting milk to the influence of air 

 in the belief that such exposure permits .of the inter- 

 change of gases that would improve the quality. In 

 practice, this process, known as aeration, is carried on in 

 different ways. In some cases, air is forced into the 

 milk ; in others, the milk is allowed to distribute itself in 

 a thin sheet over a broad surface, falling in drops or tiny 

 streams through the air. Whenever this process is ca.r- 



