AIR AS A SOURCE OF BACTERIA. 43 



The kinds of bacteria which come from this source are 

 naturally more varied than those from the milk ducts, since 

 the filth is of a varied character. In general, the bacteria 

 from this source are commonly cocci (17). By this it is not 

 meant that the rod-shaped bacteria are not found in such 

 filth, but the predominant type of bacteria are cocci. The 

 species found, however, will vary widely with conditions and 

 will depend upon the particular kind of filth that happens to 

 be attached to the animal. The filth from the cow is prob- 

 ably the largest source of bacterial contamination. 



The Air. The air has always been regarded as one of the 

 important sources of bacterial contamination, but this state- 

 ment requires a slight explanation. The ordinary out-of- 

 door air on a farm does not contain bacteria in large numbers, 

 and if the milking were done in the open, the air would not be 

 a very important source of contamination. The case is quite 

 different in the somewhat small barn or milking room where 

 milk is commonly drawn. The presence in such a room of 

 many cows, which are constantly giving off particles of dust 

 and dirt from their skin, renders the air much more liable to 

 be filled with bacteria-laden dust than is the air in the open 

 (24). Moreover, in many barns it is customary to throw 

 down hay or other dry food in the front of the cattle and 

 allow them to eat it in the same room where the milking 

 is simultaneously or subsequently carried on. The hay 

 itself is crowded with bacteria, and the dry dust from the 

 hay scatters itself readily and abundantly through the air 

 of the room. If the milking is done while the air is thus 

 filled with the dust from the hay, large numbers of bacteria 

 may settle into the milk pail. Here, again, we have a 

 conclusion that is not dependent upon theory but has been 

 readily demonstrated. It has been found by bacteriological 

 tests that the kinds and number of bacteria in the milk are 

 generally modified by the kind of food and the condition of 

 feeding. In a single experiment, made at Storrs, it was 



