BACTERIA COMMONLY FOUND IN COWS* MILK. 93 



kept for about one day. Among the determining causes 

 for the superiority of these few forms three circumstances 

 may especially be pointed out : 



1. The milk is a better nutritive medium for these 

 organisms than for their competitors. Although milk in 

 general may be considered an excellent growing place for 

 bacteria, certain kinds seem to be especially adapted to 

 development in this substratum. 



2. The temperature present is more favorable for the 

 conquering kinds than for the others. Experience shows 

 that a difference in temperature of 2-4 F. may have a 

 decided influence on the development of bacteria, a fact 

 which is apparent in a striking manner in the manufac- 

 ture of the different kinds of cheese. 



3. If the milk has become largely infected with a cer- 

 tain kind of bacteria, this is very apt to keep the superior- 

 ity, even if the milk generally speaking is not a very 

 good nutritive medium for it. Such " mass-infections " 

 of a certain bacteria frequently occur in the handling of 

 the milk on the farm. Accidents seem to play an impor- 

 tant part in this matter. In several cow stables it seems 

 to be the rule that such mass-infection takes place. This 

 was, e.g., the case in a stable where, as mentioned in the 

 preceding chapter (see p. 53), unclean straw and rusty 

 chaff were used day after day. 



Fortunately, however, it is always not the case that Jhe 

 conquering species are injurious to the quality of the milk. 

 I have seen examples where milk which was normal both to 

 taste and smell, as well as to consistency in general, con- 

 tained an immense number of bacteria which did not then 

 interfere with the quality of the milk. Among the species 

 found in such milk I have observed bacteria, which later on 



