68 THE STORY OF GERM LIFE. 



teria are not present, it will remain sweet indefi- 

 nitely. 



But it is impossible to draw milk from the 

 cow in such a manner that it will be free from 

 bacteria except by the use of precautions abso- 

 lutely impracticable in ordinary dairying. As 

 milk is commonly drawn, it is sure to be contami- 

 nated by bacteria, and by the time it has entered 

 the milk pail it contains frequently as many as 

 half a million, or even a million, bacteria in every 

 cubic inch of the milk. This seems almost in- 

 credible, but it has been demonstrated in many 

 cases and is beyond question. Since these bac- 

 teria are not in the secreted milk, they must 

 come from some external sources, and these 

 sources are the following:* 



The first in importance is the cow herself; 

 for while her milk when secreted is sterile, and 

 while there are no bacteria in her blood, neverthe- 

 less the cow is the most prolific source of bacte- 

 rial contamination. In the first place, the milk 

 ducts are full of them. After each milking a lit- 

 tle milk is always left in the duct, and this fur- 

 nishes an ideal place for bacteria to grow. Some 

 bacteria from the air or elsewhere are sure to 

 get into these ducts after the milking, and 

 they begin at once to multiply rapidly. By the 

 next milking they become very abundant in the 

 ducts, and the first milk drawn washes most of 

 them at once into the milk pail, where they can 

 continue their growth in the milk. Again, the 

 exterior of the cow's body contains them in 

 abundance. Every hair, every particle of dirt, 

 every bit of dried manure, is a lurking- place for 

 millions of bacteria. The hind quarters of a 

 cow are commonly in a condition of much filth, 



