CHAPTER III. 

 CONTAMINATION OF MILK* 



Milk as food for bacteria. The fact that milk undergoes 

 decomposition changes so readily shows that it is well 

 suited to nourish bacterial life. Not only does it contain 

 all the substances necessary for nutrition, but they are 

 diluted in such proportions as to render most of them avail- 

 able for bacterial as well as mammalian lite. 



The albumen which is in solution is readily assimilable. 

 The casein can not be appropriated directly, until it is first 

 rendered soluble, a process which occurs with those bac- 

 teria that secrete proteid-dissolving enzyms like pepsin 

 and trypsin. Of the carbon-containing compounds, the 

 fat is of little value for food as normally bacteria can not 

 act on this. The milk-sugar, however, is an admirable 

 food and the decomposition of this results in the produc- 

 tion of acids and gases. The mineral requirements of the 

 bacterial cell are so limited as to demand but little atten- 

 tion, as any organic substance contains sufficient inorganic 

 matter to satisfy the needs of the cell in the formation of 

 new cell substance. 



Milk, germ-free in Udder. Under ordinary conditions, 

 when examined in the proper manner, milk always reveals 

 bacterial life. This germ contend, however, is due to in- 

 fection from without, for in the udder of a healthy animal, 

 as secreted, the milk like the other secretions and tissues 

 of the body is normally sterile. 



Contamination Of milk. In withdrawing the milk from 



the udder, it invariably comes in contact with germ life. 



