38 PRACTICAL DAIRY BACTERIOLOGY 



laminated by the typhoid germ is dangerous. But the cattle 

 which produce milk do not suffer from typhoid fever and, with 

 the exception of tuberculosis, which will be especially mentioned 

 later, no diseases found in the intestinal canals of animals are 

 likely to be distributed to man. Hence, while a small quantity 

 of animal faeces in milk may not be an appetizing matter to 

 think of, it does not necessarily, or even probably, render the 

 milk at all likely to distribute infectious diseases to those drink- 

 ing it. Thus it follows that, although the presence of B. coli 

 may render water unsafe, because it suggests sewage contam- 

 ination, its presence in milk does not render the milk unsafe, 

 but merely indicates that there may have been a certain amount 

 of contamination with animal faeces. This fact is of universal 

 occurrence, as any one knows who has ever visited a cow stall. 



V B. coli is not harmful in itself, and animal faeces are by far less 

 . dangerous than human excreta. Clearly the presence of B. 

 1 coli in milk has a very different meaning from its presence in 

 \ water. 



Other Types of Lactic Bacteria. The two types of bacteria 

 described are by far the most important of the acid bacteria of 

 milk. Each of these, as indicated, represents a type containing 

 many varieties rather than a single species. In addition to 

 these there are other bacteria that produce lactic acid not strict- 

 ly belonging to either of these types. Some do not produce any 

 gas, but grow quite abundantly upon the surface of culture 



\ media, sometimes producing small, and at other times quite 

 large, colonies. It is impossible in this work to attempt any 

 description of these forms. Although there are numerous va- 

 rieties of lactic bacteria, in the vast majority of cases milk 

 is soured by one of the two types above mentioned. Whether 

 the one or the other of these types will be found to cause the 

 spontaneous souring in any sample of milk cannot be predicted ; 

 for it is partly dependent upon temperature. If the milk has 

 been kept at 70 or lower, it will, in most cases, be soured by 



