140 AGRICULTURAL BACTERIOLOGY 



to throw the dust from these sources into the air facilitates 

 the passage of some of it into the milk. The particles settle 

 rapidly. Therefore, if dust-raising operations, such as 

 bedding, brushing the cattle, and feeding dry feed are car- 

 ried out some time before the milking-tiine, the contamina- 



Fig. 30. Contamination from the Air 



A culture plate exposed for thirty seconds in a dusty stable shows numerous 

 colonies of bacteria and molds 



tion of the milk from the air will be slight. The amount 

 of foreign matter introduced into the milk from the air is 

 very small compared to that introduced from other sources. 

 The types of microorganisms found in the air are not 

 those primarily concerned in the spoiling of milk. The 

 contamination of milk from the air is therefore relatively 

 unimportant, both quantitatively and qualitatively. Never- 

 theless, the contamination from this source should be 



