SOURCES OF BACTERIA IN MILK 23 



per c.c. It is clear that if such quantities of organisms pass into 

 the general milk, they will rapidly pollute the entire quantity 

 which might otherwise, at the outset, have been comparatively free 

 from germs. Ward and others have pointed out that the species 

 of bacteria normally inhabiting the ducts are limited to a few. It 

 appears that only certain kinds of bacteria, including some species 

 of streptococcus, are able to live at this site. These species, as a 

 rule, are more or less persistent. The lactic acid group of organisms 

 do not appear to inhabit the milk duct, but probably gain entrance 

 to the milk from sources external to the cow. 



Two other agencies contributing to contamination at the milk- 

 ing time are the milker and the byre. The^milker's hands and 

 sometimes his clothes may convey bacteria to the milk. Clothed 

 in dust-laden garments, and frequently characterised by dirty hands, 

 the milker may readily act as an excellent purveyor of germs. Not 

 a few cases are also on record where it is certain that milkers have 

 conveyed germs of disease from some infectious case in their 

 homes, such as scarlet fever. Under the more efficient registration 

 of such diseases, which has recently been a feature in the policy of 

 the more public spirited dairy companies, the danger of infection 

 from this source has, however, now been considerably reduced. 



The influence of the barn air, and the cleanliness or otherwise 

 of the barn itself, is obviously great in this matter. We do not 

 suggest that the air of byres is a medium in which bacteria live or 

 multipl}\ The air-organisms to which we refer are in point of 

 fact dust and dirt organisms present in the air only at times of 

 molecular disturbance, and having their origin in dry fodder, hay, 

 straw, etc., as well as the ungroomed surface of the cow's body. 

 But such disturbance at milking time is actually a normal state 

 of affairs. We know that moist surfaces retain any bacteria lodged 

 upon them, and that a wet perimeter results in a germ-free or 

 nearly germ-free atmosphere. But in a dry byre the air is often 

 heavily laden with microbic life. The evidence obtainable, if 

 evidence be necessary, on this point is two-fold. There is the mass 

 of evidence laid before the Royal Commission on Tuberculosis 

 respecting the evil infection and predisposing influences of the 

 byre air on cattle in the direction of conveying tuberculosis. Sir 

 George Brown, Sir Richard Thorne Thorne, and many other 

 authorities, have again and again drawn attention to the bad state of 

 the air in byres. The second and still stronger evidence is derived 

 from experimental examination of the air of byres. Russell, Conn, 

 and other American bacteriologists, as well as many workers in 



