CHAPTEK III 



THE BACTERIA FOUND IN MILK 



IN the preceding chapter the very numerous sources whereby 

 bacteria may be introduced into milk have been considered 

 and discussed. The present chapter gives some account of the 

 chief groups of bacteria likely to be present. 



In the first place, it must be realised that it is scarcely 

 justifiable to speak of " milk bacteria " in the same way as we 

 speak of manure bacteria, sewage bacteria, etc., thus implying 

 that there are certain bacteria or groups of bacteria which are 

 characteristic of these substances and universally present. 

 The sources of pollution of milk are so many and varied that 

 the bacterial content is very complex, while it is further com- 

 plicated by the fact that milk is a suitable nutritive medium 

 for most organisms. On the other hand, certain groups of 

 bacteria are especially prevalent in milk, and some measure of 

 selective action is undoubtedly exhibited. Two lines of de- 

 scription may be adopted. On one plan, all the different 

 organisms which have been found in milk may be classified 

 and described as milk bacteria. With present knowledge such 

 a catalogue of bacteria is of practically no value from the 

 public health standpoint. In the first place, many of the 

 descriptions of these bacteria are so scanty as to be practically 

 valueless, while probably the same bacillus is described over 

 and over again under fresh names. Again, such a catalogue of 

 organisms must be very incomplete, the sources of bacteria in 

 milk being so numerous. Even if a fairly complete and 

 accurate register of all the bacteria likely to be found in milk 

 samples was compiled it would not be of much practical service 

 for public health work, since for this what is required is not 

 a knowledge of all the bacteria which may be present in milk, 



27 



