SOURCES OF MILK BACTERIA 153 
Milk Utensils.—The most prolific sources of bacteria are the 
milk-pails and other dairy utensils, in which the bacteria remain 
alive from one milking-time to the next. On an ordinary farm 
these utensils are rarely, if ever, washed bacteriologically clean. 
Bacteria 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. Even live steam, as ordi- 
narily used, a few seconds on each pail does not completely sterilize 
the utensils. 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 and then equally thoroughly 
dried. 
When milking machines are used, they are likely to cause the 
addition of many bacteria to the milk. The long rubber tubes fur- 
nish admirable places for bacteria to live and multiply unless they 
are kept in some disinfecting solution between milkings. When 
properly used, milking machines do not add appreciable numbers 
of bacteria, but on many farms, either through ignorance or care- 
lessness, the tubes of the milking machines teem with bacteria 
that are washed into the milk when the cows are next milked. 
Another large source of the bacteria in milk is the milk can. 
When the cans are supposed to be clean as returned to the farmer 
by the milk distributing company, most farmers assume they need 
no further cleansing. The odor of these cans, however, often 
suggests the contrary, and experiments have shown that they are 
the source of many milk bacteria: 
~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. Fresh, 
out-of-door air does not contain many bacteria, ‘and if milking 
cotild take place in the open air, this source of contamination would 
