52 Dairy Bacteriology. 



the lowest, 100,000 germs, while the maximum number 

 was less than 4,000,000 per cc. This range in numbers 

 is much less than is usually found in the milk- supply of 

 our large cities. 



55. Kinds of bacteria in milk. The number of bac- 

 teria in milk is not of so much consequence as the kind 

 present. While milk may contain forms that are inju- 

 rious to man, still the great majority of them have no 

 apparent effect on human health. In their effect on 

 milk, the case is much different. Roughly, we may di- 

 vide them into three classes, depending upon their action 

 in milk. 



1. Bacteria that exert no appreciable effect in milk. 



2. Bacteria that are beneficial by reason of the products 

 which they form. 



3. Bacteria that are injurious on account of the effect 

 which they produce in milk. 



A suprisingly large number of bacteria that are found 

 in milk belong to the first class. Undoubtedly they af- 

 fect the chemical characteristics of the milk somewhat, 

 but not to the extent that it becomes physically percep- 

 tible. 



Those species that are concerned in the production of 

 proper flavor and aroma in butter, and which are also 

 concerned in the development of acid and possibly asso- 

 ciated with formation of cheese flavor represent the sec- 

 ond type. Many of these organisms are lactic acid pro- 

 ducing, but in addition to these, some of the casein 

 ferments are also associated with aroma production in 

 butter. 



The third class includes those species that are able to 

 produce deleterious and undesirable flavors in milk and 

 milk products. The majority of the abnormal fermenta- 

 tions of milk referred to in this chapter come under this 



