154 BACTERIA IN MILK 
be almost excluded. In a close barn, however, conditions are 
somewhat different. Hay, dirt, cobwebs, soiled bedding and other 
dry dust-producing materials are allowed to accumulate, and par- 
ticles from any of these sources are likely to be dislodged and 
float for a time in the air. If dry hay or other dry food is thrown 
down in front of the cattle, a large amount of dust will arise and 
spread through the air of the stable. Such dust contains bacteria, 
some of which will settle into the milk-pail during milking. The 
total number coming from this source, however, is comparatively 
small. 
The Milker.—Of late years it has become evident that the 
bacteria coming from the milker or other persons in the dairy are 
among the most serious. This is not so much because of the 
number of bacteria that may enter the milk from this source, but 
because of their types. In ordinary dairies the milker rarely 
makes any special toilet before milking, but is liable to perform 
this task in old, soiled clothing, with no attempt at cleaning his 
hands. Under these circumstances, while, so far as concerns 
numbers, he is not so great a source of bacteria as the cow, some 
of these organisms are sure to fall from his hands or clothes into 
the milk-vessels, especially if he adopts the filthy habit of wet 
milking. ‘The number of bacteria from such a source is, probably, 
not great, and does not add materially to the bacterial content. 
But in one respect these bacteria assume a more important signifi- 
cance. The bacteria which produce diseases in one animal do not 
necessarily produce diseases in other animals. Those which pro- 
duce 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, bacterial 
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 
more dangerous than those which come from any other source. 
