CHAPTER XXXV 

 KINDS OF BACTERIA IN MILK 



Milk may be contaminated by bacteria from the 

 cow's udder, as well as by organisms from the soil, 

 manure, bedding, air, water, milk utensils and the 

 milker. Owing to these various sources of infection, the 

 number of species found in milk, at one time or another, 

 is large. However, the bacterial flora of freshly drawn 

 milk soon begins to undergo a change. The struggle 

 for existence that sets in, ends disastrously for many 

 of the species originally present, and they either disap- 

 pear entirely, or are crowded back so as to play but an 

 insignificant role in the subsequent changes in the milk. 

 The elimination or suppression of these species leaves 

 the entire field to a comparatively few organisms, — 

 organisms that may be regarded as normal milk-bac- 

 teria. 



Species of bacteria in milk. — The bacteria commonly 

 occurring in milk may be conveniently divided into 

 three groups. 



The first of these includes the important lactic fer- 

 ments, organisms capable of fermenting milk-sugar with 

 the formation of lactic acid. The spontaneous souring of 

 milk, with the characteristic curd formation, is due to 

 these bacteria. They are prominently represented by 

 X (369) 



