142 BACTERIA IN MILK. 
ination. 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 is crowded with bacteria, many of which 
are alive and will settle into the milk-pail during milking. The 
common practice of keeping cattle in the same room where they 
are milked is thus very productive of a large source of bacterial 
contamination. 
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 and face. 
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 significance. The bacteria 
which produce diseases in one animal 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, 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 more dangerous than those which 
come from any other source. 
TYPES OF BACTERIA FOUND IN MILK. 
Many different types of bacteria get into milk from these various 
sources. Some of them are useful, some are of no particular signifi- 
