266 BACTERIOLOGICAL ANALYSIS OF MILK. 



standard has also been found useful in testing certified milk, 

 as mentioned on the previous page. But for the general milk 

 supply of a large city it has, up to the present time, been 

 found quite impracticable to suggest any bacteriological 

 standard without excluding too large a portion of the milk 

 which will be brought into the city. Moreover, it seems 

 by no means sure that such a standard would be of much 

 practical value, because, even though the numbers be large, 

 the milk may be perfectly wholesome if they are of the 

 normal lactic type, whereas a much smaller number of bac- 

 teria in another sample of milk might make it decidedly 

 injurious if the bacteria should be of a different character. 



These various facts raise the question whether a bacteri- 

 ological analysis of milk which shall differentiate the different 

 kinds of bacteria from 'each other is possible and practical. 

 Is it possible to devise some means of analysis of the bacteria 

 in milk which shall give the numbers of the different kinds 

 of bacteria, separating the normal forms from those that ren- 

 der the milk suspicious? If we could do this the practical 

 analysis of city milk might be more useful and might become 

 an efficient means in the hands of boards of health in pro- 

 tecting the public from the dangers in its milk supply. There 

 has, hitherto, been no attempt made to develop such a method 

 of differential analysis of milk and, indeed, at the present 

 time we know too little in regard to the relations of the differ- 

 ent species of bacteria to the wholesomeness of milk to make 

 such an analysis absolutely reliable. Nevertheless, even 

 an approximate qualitative analysis of the bacteria in the 

 milk may be useful in detecting the quality of samples of 

 milk from unknown sources. Such approximate analysis is 

 at least possible. 



SIGNIFICANCE OF A QUALITATIVE ANALYSIS. 



We must notice again a few facts in regard to the different 

 types of bacteria. It is practically impossible, by any ordi- 

 nary means, to detect in milk the presence or absence of the 



