SOURCES OF COMMON MILK BACTERIA 



amount depend upon the condition of the cow. There will be 

 loss on cows during the pasturing season than during their life 

 in the barn in the winter. It will vary much with different 

 foods. Dry foods, like hay, appear to- furnish more bacteria 

 in the manure than moist 

 foods, and the milk sub- 

 sequently receives them. 

 It frequently happens 

 that a certain food fed 

 to the cows injuriously 

 affects the keeping of 

 the milk because the 

 bacteria, which the food 

 furnishes, find their way 

 into the milk from the 

 filth on the cow ; for ex- 

 ample: the feeding of 

 turnips. 



The Air. In earlier 

 studies of bacteriology, it 

 was thought that the greatest source of bacterial contamination 

 was the air. More careful study of later years has produced con- 

 siderable change in this belief. Fresh air out-of-doors does not 

 contain many bacteria, and if milking could take place in the open, 

 free air, this source of contamination would be almost excluded. 

 In a close barn, however, conditions are very different. The 

 motions of the crowded cattle are dislodging bacteria from their 

 skins, which float for some time in the air. Hay, dirt, cobwebs 

 and other dry dust-producing materials are allowed to ac- 

 cumulate. Dirty straw bedding is another source of air con- 

 tamination. (Fig. 34.) The general manner of feeding the 

 animals is even a larger source of contamination. If dry hay, 

 or other dry food, is thrown down in front of the cattle, a large 



1 Backhaus. Milchztg., i>. 357, 1897. 



F1G - 33 NUMEROUS COLONIES OF BACTERIA 

 GROWING FROM COW'S HAIR PLACED IN 

 GELATIN 



