CHAPTER II 



TYPES OF BACTERIA FOUND IN MILK 



IN the study of the types of bacteria that may be found 

 in milk, three different factors are to be considered: I. Their 

 action on milk, and its relation to all who deal with this product. 

 2. Their relation to butter and cheese making. 3. Their rela- 

 tion to the human organism and, therefore, their effect upon 

 the persons using the milk as food. Certain bacteria that are 

 troublesome to the dairyman are perfectly wholesome to the 

 consumer, while, on the other hand, some bacteria that are very 

 injurious and even fatal to the consumer are of no special signif- 

 icance in dairying, so far as their effect upon milk is concerned. 

 We shall also find that organisms which are of great nui- 

 sance to a person dealing in milk are favorable and, indeed, 

 indispensable to butter and cheese making. These problems 

 must, therefore, be considered independently. 



It will be most convenient to study milk bacteria under the 

 heads of normal and abnormal types. Since milk does not 

 usually contain any bacteria at the time when it is secreted 

 from the milk glands, there are really no such things as normal 

 bacteria. Nevertheless, it is practically impossible ' to procure 

 milk from any cow, no matter under how cleanly conditions it 

 may be kept or how carefully we work, in such a manner that 

 it will be sterile by the time it reaches the milk pail. We may, 

 therefore, recognize bacteria as inevitable, and the distinction be- 

 tween normal and abnormal bacteria will, therefore, be as 

 follows: Normal bacteria are those that under all ordinary cir- 

 cumstances are practically certain to be found in milk; their 

 presence must always be expected, and it is practically im- 

 possible to avoid them. Abnormal bacteria are those which are 



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