94 MODERN DAIRY PRACTICE. 



exerted a more or less injurious influence on the butter 

 or the cheese made from the milk. 



Some bacteria may furthermore appear in the milk 

 which do not in themselves have the power to change 

 appreciably its quality, but which prepare favorable con- 

 ditions for other, injurious bacteria. As a transition 

 group between these organisms and those directly de- 

 structive of the milk, some species may be included that 

 are able both to change the quality of the milk to a 

 considerable extent and to prepare a good field for other 

 bacteria, which in their turn produce other kinds of fer- 

 mentations. 



CLASSIFICATION OF BACTERIA FOUND IN MILK. 



In trying to classify the common forms of bacteria 

 found in milk, I have separated them into the following 

 four groups: 



I. Indifferent bacteria. 



II. Bacteria indifferent in milk, but active in the milk 

 products. 



III. Indirectly injurious bacteria. 



IV. Injurious bacteria. 



I. Indifferent Bacteria. The species belonging to this 

 group are of course of small interest in studying the prob- 

 lem of the bacteriology of the dairy, and will therefore not 

 be described in detail here. In deciding certain questions, 

 as, e.g., whether a certain sample of milk has been infected 

 by bacteria in the air or by such originating in manure 

 particles, the indifferent bacterial impurities may be of 

 some importance. They seem, however, to show such a 



