MICRO-ORGANISMS IN MILK 293 



carry the germs of intestinal diseases of man by visiting privies 

 and urinals; or the germs of throat and lung diseases by feeding 

 on sputum; or, finally, the germs of skin diseases by alighting on 

 human beings suffering from such troubles. 



Esten and Mason estimated the number of bacteria on 414 

 flies, and recovered from 550 to 6,600,000 from individual insects. 

 The average for the 414 flies was 1,250,000. 



The material used for the bedding of cows may be an important 

 source of dust. Wood shavings are usually recommended as the 

 most cleanly, as they do not contain much dust and soon absorb 

 enough moisture to hold the dust. Straw and hay, however, 

 may emit clouds of dust when stirred by movements of the ani- 

 mal, and are not as absorbent as wood shavings. When straw or 

 hay are used for bedding it should be frequently renewed, and 

 even then operations are liable to create dust. Wood shavings 

 are cheap and can be readily obtained, so that there can be no 

 serious objection to their use. 



It would appear from what has been said that the stable air 

 is in a condition of greater or lesser saturation with dust and 

 that it must be a formidable factor in contributing bacteria to the 

 milk. Unfortunately, there are not many exact investigations 

 available that throw light on this question. In most cases the 

 number of bacteria in stable air has been estimated by exposing 

 culture-media in Petri dishes in different parts of the stable. This 

 obviously is a crude method and, while it may show the presence 

 of large numbers of micro-organisms in the air, it does not show 

 the number by which the germ content of the milk is increased 

 thereby. It is true that it has been sought to attain this object 

 by milking the same set of cows alternately in dust-laden air and 

 in a relatively pure one, and then enumerating the germs of the 

 milk. This method, however, does not differentiate between the 

 dirt that drops into the milk from the animal during milking from 

 the dust that is blown into it. Therefore, a more refined method 

 is necessary to inform us as to the increase of the germ content 

 due exclusively to the stable air. This subject has been ex- 

 haustively investigated by Ruehle and Kulp by means of an 

 ingenious apparatus which the authors call their "tin cow." The 

 "tin cow" is an artificial udder made of tin; two "teats" are 

 attached to the udder and are made of rubber tubing with pieces 

 of glass tubing, flattened at the end. The "tin udder" is sup- 

 ported so as to give it the same protection from the air as the 

 body of the cow, and is placed at such height from the pail as 

 to give the same distance that obtains in actual milking. After 

 the "tin udder" is covered with two thicknesses of closely woven 

 cheesecloth and sterilized, it is filled with sterile water. The 



