CHAPTER VI 



DETERMINATION OF BACTERIA IN MILK 



Bacteria as a measure of dirt in milk. Since a 

 chief source of contamination of milk with bacteria is 

 in dirty surroundings, the relative number of bacteria 

 in milk has come to be largely accepted as an index 

 of its quality with regard to cleanliness. As a matter 

 of fact, in certain of the higher grades of the market 

 milk, notably in "certified milk," the standard of 

 quality is fixed by the number of bacteria per cubic 

 centimeter found in the milk, and if the number so 

 found exceeds a certain amount the milk cannot be 

 graded as "certified." For these reasons it is neces- 

 sary to make frequent determinations of the bacterial 

 content of milk. This is best and most accurately 

 done by a trained bacteriologist in a well-appointed 

 and equipped laboratory. However, the simple deter- 

 mination of the number of bacteria in a given amount 

 of milk is not a difficult operation, nor does it require 

 a very elaborate or expensive equipment. There are 

 reasons why a dairyman, particularly one producing 

 certified milk, should have the means at hand for 

 making his own determination of the bacterial content 

 of his milk, the chief reason being that it enables 

 him to control the conditions and work from day to 



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