CHAPTER V 



THE ENUMERATION OF BACTERIA IN MILK 



An approximate determination of the total bacteria in 

 milk by plating on solid media has, for many years, been one 

 usually made in connection with the examination of milk, and, 

 although later work has shown that the mmiber so obtained 

 is usually but a small fraction of the total nvimber present, 

 these methods have been generally retained on account of their 

 convenience, and the results are usually described as the total 

 bacterial counts. There has been considerable difference of 

 opinion amongst sanitarians regarding the value of this test, 

 for, whilst some regard the total mmiber of minor importance, 

 others beheve that much valuable information can be obtained 

 by this determination alone. The fact that the great majority 

 of regulations for the sale of milk, where regulations have been 

 enacted, contain no other clause with reference to bacteria 

 than a maximum number clause, is sufficient to show the trend 

 of opinion on this subject. Those who deprecate the value of 

 the total bacteria enumeration take the stand that the large 

 majority of the bacteria usually found in milk are harmless 

 saprophytes, and that their determination is more or less a 

 waste of time and labour. Whilst the former statement is 

 undoubtedly true, the latter must be emphatically denied. 

 Until bacteriological technique becomes so developed that 

 routine methods can be applied for the detection of pathogenic 

 organisms, those employed in milk examination must be con- 

 tent with the inferential teste obtained by determination of the 

 saprophytes. As has been shown in the preceding chapter, 

 milk drawn with reasonable aseptic precautions from the 

 udders of cows contains but few bacteria, and, if properly 



113 



