QUALITATIVE BACTERIOLOGICAL ANALYSIS. 267 



bacteria producing tuberculosis, scarlet fever, typhoid fever 

 or diphtheria. The detection of the bacteria producing these 

 diseases, even .when possible, requires so much work and is so 

 uncertain as to be impracticable of adoption in the analysis of 

 milk. Hence, no practical analysis of milk, at the present 

 time, will enable us to detect the presence of the exciting 

 causes of any of these distinctively contagious diseases. 



We have learned that the ordinary bacteria in milk may be 

 divided into three chief classes : ( i ) The lactic bacteria, 

 which are most abundant in samples of milk after it is a few 

 hours old. Most of these organisms probably have little or 

 nothing to do with rendering the milk unwholesome, although 

 the bacillus of typhoid fever and possibly that of summer 

 complaint belong here. (2) The enzyme bacteria, many of 

 which produce putrefactive products, and are most likely the 

 organisms associated with the production of some of the 

 digestive disturbances attributed to milk. (3) Bacteria 

 which produce no distinctive action upon milk. We have, as 

 yet, no knowledge as to whether this last group is associated 

 with the production of intestinal disturbances. There may 

 be among them some bacteria that are distinctively injurious, 

 but at the present time we really know nothing about the 

 matter. 



It is possible, by a simple modification of the common bac- 

 teriological methods of study, to differentiate these three 

 types of milk bacteria from each other. While such a dif- 

 ferentiation will not be sufficient to determine accurately 

 whether a sample of milk is wholesome, it will certainly bring 

 us much closer to such a conclusion than simply counting the 

 numbers. Moreover, this differential analysis will frequently 

 enable us to determine whether the milk has been badly con- 

 taminated by uncleanliness in the original dairy, or has simply 

 been kept until normal harmless bacteria have had a chance 

 to multiply. 



