CONTAMINATION OF FOODS 139 



of milk; hence, this source of contamination of milk, al- 

 though one that can not be avoided, is of small commercial 

 importance. At times the udder may be invaded by bac- 

 teria upon which the milk has no germicidal action. 

 Growth will then be unchecked and serious trouble may 

 result. 



The milk at the time of withdrawal generally contains a 

 few hundred bacteria per cubic centimeter. Great differ- 

 ences in individual animals are to be noted. In the same 

 herd two animals were found that showed an average bac- 

 terial content of more than 30,000 per cubic centimeter dur- 

 ing a period of over one year. Another animal, kept under 

 the same conditions, gave milk in which the average germ 

 content was but 800 per cubic centimeter. The mixed milk 

 of a number of cows will contain from a few hundred to a 

 thousand, or more bacteria per cubic centimeter, even when 

 the contamination from outside sources has been prevented 

 as far as is practically possible. 



Since the greater number of bacteria are found in the 

 lower part of the udder, and hence in the first milk drawn 

 from each teat, it is the custom to discard the fore-milk, or 

 the first few streams from each teat. This reduces the 

 number of bacteria found in the milk, but will have little, 

 if any, influence on the keeping properties of the milk, since 

 the organisms found in the udder grow very slowly at ordi- 

 nary temperatures. 



Contamination from the air. The air in a stable con- 

 tains varying numbers of bacteria adherent to the dust 

 particles. Some of the manure becomes dry, and is ground 

 into fine particles by the movements of the cattle. This is 

 supplemented by the soil that is brought into the stable on 

 the hoofs of the cattle. The dry feed is covered with dust 

 and minute particles of soil ; the bedding and coat of the 

 cow are also covered with dust. Any operation that serves 



