Contamination of Milk. 59 



fection, and is also still further amplified in following 

 chapter. 



Aeration. Practical experience has long demonstrated 

 the advantage of aerating the milk as soon after milking 

 as possible. This is accomplished in a variety of 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 and fall some distance so that it is brought inti- 

 mately in contact with the air. The benefit claimed for 

 aeration is that foul odors and gases which may be present 

 in the milk are thus allowed to escape by bringing the 

 finely divided milk into contact with the air. As ordi- 

 narily practiced, aeration is usually combined with cooling, 

 and it is noteworthy that the most effective aerators are 

 those that cool simultaneously. Under these conditions, 

 the keeping quality of the milk is increased, but where 

 milk is simply aerated without cooling, no material benefit 

 in keeping quality is observed. A satisfactory scientific 

 explanation of the advantages of aeration has not yet been 

 made. It is difficult to see how the process can have any 

 effect on the bacterial life in the milk. Its influence, un- 

 doubtedly, is on the odors directly absorbed by the milk. 



Infection of milk in the factory. The problem of proper 

 handling of milk is not entirely solved when the milk is 

 delivered to the factory or creamery, although it might be 

 said that the danger of infection is much greater Avhile the 

 milk is on the" form. Then, too, contamination of milk at 

 time of withdrawal gives a longer period of incubation for 

 the bacteria in the milk, and consequently intensifies the 

 effect which they produce. 



In the factory, infection can be minimized because ef- 

 fective measures of cleanliness can be more easity applied. 



