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 sourcTe of contam- 



