SOURCES OF MILK BACTERIA. 141 
shed from her body by the -movements of her flanks, by the switching 
of her tail, and by the rubbing of her skin by the milker. Since the 
milk-pails are generally widely opened, they receive a large amount 
of this filth, which consists of almost every conceivable kind of 
material. Besides excrement there are insect wings, grass, straws, 
hairs, and many other small particles, all bacteria laden. 
Milk-vessels. The next prolific sources of bacteria are the milk- 
pails and other dairy vessels, in which the bacteria remain alive 
from one milking-time to the next. On an ordinary farm these 
vessels are rarely, if ever, washed bacteriologically clean ; for washing 
in hot water with subsequent drying in the sun is wholly insufficient 
to remove the bacteria. They are sure to remain in the vessels, 
clinging in corners and cracks, partly dried perhaps, but alive and 
ready to begin active life just as soon as they are supplied with the 
food which comes to them in the next lot of milk drawn. The 
ordinary farm has no really effective means of washing milk-vessels. 
Even live steam, as ordinarilly used, a few seconds on each pail, will 
not do it completely. Many a troublesome experience of the milk 
dealer in warm weather is attributable directly to imperfectly 
washed milk cans, and disappears at once when all the milk-vessels 
are thoroughly sterilized by live steam. So far as numbers are con- 
cerned, those in the milk-vessels probably form the largest source of 
bacterial contamination. 
The Air. Other sources furnish bacteria to a less extent. Some 
doubtless come from the air. In earlier years it was thought that 
this was a great source of contamination, but now we know that 
the air bacteria are ordinarily of little importance, although some- 
times they may be a source of trouble. Fresh, out-of-door air does 
not contain many bacteria, and if milking could take place in the open 
air, this source of contamination would be almost excluded. In a 
close barn, however, conditions are very different. The motions of 
the crowded cattle dislodge bacteria from their skins. Hay, dirt, 
cobwebs, soiled bedding and other dry dust-producing materials 
are allowed to accumulate, and particles from any of these sources 
are likely to be dislodged and float for a time in the air. The gen- 
eral manner of feeding the animals is even a larger source of contam- 
