4O SOURCE OF BACTERIA IN MILK. 



+ 



other species of streptococci. Streptococci, indeed, are 

 found so frequently that they may probably be regarded as 

 normal inhabitants of the milk ducts (35). These milk 

 streptococci, however, are not all alike, and a variety of types 

 have been described. Further, it has appeared that the species 

 of bacteria found in the milk gland of any cow are tolerably 

 constant. Examination of the fore milk of a cow extend- 

 ing over a considerable interval of time shows that certain 

 species of these bacteria are quite persistent, being found in 

 the milk over a long period of time. The milk from the 

 four teats of the same cow may show a slightly different 

 bacteriological content, and the bacteria remain tolerably 

 persistent in each of the four quarters. 



The relation of these streptococci ' to the .wholesomeness 

 of milk is as yet not determined. Some of the common strep- 

 tococci found in fore milk have no visible effect upon the 

 milk, neither souring it nor curdling it, nor having any 

 other visible influence upon it. Others, however, appear 

 to render it slightly alkaline, a fact which indicates that 

 they do produce certain changes in the milk. But the 

 changes are at all events very slight. It is quite certain, 

 however, that occasionally some of the dairy troubles which 

 are attributable to milk bacteria come from the bacteria 

 which live in the udders. These problems have not as yet 

 been satisfactorily worked out in many cases, but at least in 

 one instance a bitter milk infection has been traced to bac- 

 teria that come directly from the milk ducts (80), and were, 

 therefore, in all probability inhabitants of the milk duct ; 

 a single infection of blue milk has been similarly located. 

 It is quite probable that some other milk infections are trace- 

 able to bacteria from a like source, but very little is as yet 

 known in regard to this matter. 



It is important to notice that the lactic bacteria, which 

 have, from the beginning of the study of dairy bacteriology, 

 been looked upon as the dairy bacteria par excellence, do not 



