SOURCES OF COMMON MILK BACTERIA 69 



not great and does not add materially to the bacterial content. 

 But in one respect these bacteria assume a more important 

 significance. The bacteria which produce diseases in one an- 

 imal do not necessarily produce diseases in other animals. 

 Those which produce diseases in cattle, with some exceptions 

 (tuberculosis), do not usually have the same effect on man. 

 But it is evident that any disease germs that may be present 

 in one man are just the kind that can develop in any other 

 human being. Therefore, the bacteria contamination from 

 human sources is more dangerous to other human beings than 

 any infection from animals. For this reason the bacteria which 

 enter the milk from the milker are liable to be much more 

 dangerous than those which come from any other source. This 

 we shall consider in the next chapter. 



SOURCES OF COMMON MILK BACTERIA 



While at present no complete statement can be made as to 

 the sources of all the milk bacteria, a few facts concerning 

 some of the more common are of value. 



The common Streptococci and other coccus forms appear to 

 come mostly from the udder directly. In some cases this may 

 indicate a diseased condition of the udder, but even from the 

 healthiest cow the milk will be sure to -show these types at the 

 outset. 



Bact. lactis acidi is derived, in most cases, not from the udder 

 but from the dust of the air, or the hair of the cows, and pos- 

 sibly in some cases from the faeces. But beyond doubt the largest 

 source of these germs in the ordinary dairy is the milk vessels. 

 This species grows abundantly in milk, and will always be left 

 in large numbers in the milk vessels, even after thorough wash- 

 ing. Hence, milk vessels are its chief source. Its original 

 source has not been so easy to trace. It is sometimes found 

 in the feed of the cattle, artd Barthel has found it upon the 



