28 Dairy Bacteriology. 



CHAPTER III. 



CONTAMINATION OF MILK. 



Spoiling of milk. Materials of animal origin are pe- 

 culiarly prone to undergo changes, rendering them unfit 

 for use, and of these, milk is exceedingly susceptible to 

 such changes. This is due to the fact that the composi- 

 tion of milk is especially adapted to bacterial growth, 

 and that the opportunity for entrance of such organ- 

 isms is likewise such as to permit of abundant contam- 

 ination. The consequence is that milk readily under- 

 goes fermentative changes, due to the development of 

 one or another type of micro-organism. 



Milk, a suitable bacterial food. While milk is de- 

 signed by nature for the nourishment of- mammalian 

 life, it is, curiously enough, equally well adapted to the 

 growth of these lowest forms of vegetable life. The nu- 

 tritive substances required by bacteria are here suffi- 

 ciently dilute to make possible rapid growth. 



Milk also contains all the necessary chemical sub- 

 stances- to make a suitable bacterial food supply. Of 

 the nitrogenous compounds, albumen is in a readily as- 

 similable form. Casein, the principal nitrogenous con- 

 stituent of milk, exists in an insoluble condition, and 

 cannot be directly utilized, until it is acted upon by di- 

 gesting enzymes. The fat in milk does not readily de- 

 compose, and while there are a few bacteria capable of 

 splitting this substance, the majority of organisms are 



