174 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
depended upon to protect milk from contamination. 
They do not keep out bacteria, but hold back only the 
larger particles of dirt. Some of these particles are sub- 
sequently dissolved by milk and carried through the 
strainer, while bacteria are washed off of the insoluble 
particles remaining on the strainer. It is also difficult 
to clean strainers of this kind thoroughly. Particles of 
dirt become entangled in the meshes of the wire gauze, 
especially at the periphery where it is soldered to the tin, 
and it is difficult to remove them, while the cheese cloth 
requires much care in cleaning. It should be rinsed in 
cold water, washed in hot water containing two per cent. 
of soda, again rinsed in cold water and then wrapped in 
a clean cloth and sterilized in a steam chest. If a steam 
chest is not available, it should be put into a thick paper 
sack and placed in a stove oven and kept there until the 
sack begins to scorch. A strainer composed of a thin 
layer of absorbent cotton is much more effective and it 
can be thrown away after being used and thus save the 
labor of cleaning. Some of the bacteria are apparently 
enmeshed in the cotton and kept out of the milk. The 
use of a cotton strainer has reduced the bacterial content 
of the milk nearly one-third in some tests. Coarse cot- 
ton-flannel and turkish toweling are also used for strain- 
ers, but they are no more effective than cheese cloth. 
Bacteria cannot be kept out of milk by strainers nor 
can they be removed by these contrivances after they 
have entered the milk. The coarse particles of dirt may 
be strained out, but the most objectionable part of the 
dirt the bacteria, will remain. Much more satisfactory 
results will be obtained by cleanliness and care in milking 
and in the subsequent handling of the milk. 
In some receiving stations and distributing plants, 
