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quite impossible. On the other hand it does not seem improbable 
that the cover of the well may have minute cracks between the boards, 
even where inspection fails to reveal any such defects, and that filth 
from the shoes may wash down through these cracks. It is to be 
assumed that this is the case with the well just described and other 
similar wells. 
The presence of B. coli in open springs and cisterns may also be 
more readily explained by assuming its introduction through faulty 
manipulation than by pollution from seepage through the ground. 
In the case of open springs it seems indeed almost unavoidable that 
filth brought in on the shoes should be introduced into the spring. 
In bringing the milk from the cow barn to the dairy more or less cow 
dung is unavoidably tracked on the feet into the dairy and where 
there is an open spring it must be defiled from time to time. As cow 
dung as well as human feces contains B. coli, this would account for 
the frequent presence of the organism in the water from springs at 
dairies. 
But whatever its source, B. coli should be specially guarded against 
in water used for washing vessels for containing milk. F or aside from 
the fact that its presence may indicate fecal pollution, human or 
animal, it is likely to get into the milk, and when this occurs it multi- 
plies rapidly and causes changes in the milk which render it unwhole- 
some, particularly for children. 
Still if the supposition stated above is correct that B. coli gains 
access to the water through careless methods in bringing filth on the 
shoes or otherwise, this can be readily remedied in many cases by the 
means recommended in the article on “ Sanitary water supplies for 
dairy farms” in this same volume. 
A careful examination should make it possible to decide the cases 
in which the water supplies can be guarded against pollution in the 
manner indicated and those cases where no remedy seems available. 
Even in cases where the chemical and bacteriological examinations 
fail to show pollution, it is sometimes apparent from a sanitary sur- 
vey that a water supply is exposed to accidental pollution from care- 
lessness and that this danger could be avoided by proper coping or 
otherwise. Dairies 103 and 119 in Maryland are examples in point. 
These dairies each obtain water from open springs and the location 
is rendered bad by the fact that in both cases the barnyard drains 
toward the spring and the surroundings in both cases are very slov- 
enly. It would seem that pollution from animal feces at least would 
most certainly occur at frequent intervals. Yet the chemical and 
bacteriological examinations in these cases would indicate excep- 
tionally pure water. The fact that the springs are both very bold 
and the supply of water is constantly being renewed in large quanti- 
