CHAPTER VI. 



PRESERVATION OF MILK FOR COMMERCIAL 

 PURPOSES. 



IN Chapter III it has been shown how milk becomes 

 contaminated with various kinds of bacteria which find in 

 this liquid most favorable conditions for development. The 

 result of this contamination is that the period during which 

 milk has a commercial value for food purposes, either in 

 the form of milk, or milk products, such as butter and 

 cheese, is greatly lessened, thereby causing losses of consid- 

 erable economic importance. 



Moreover, it has been further shown (Chapter Y) that 

 this food product which is so admirably adapted to serve 

 as food may become infected with disease-producing organ- 

 isms, and so be the means of disseminating contagion. 



From these two points of view, therefore, 



1. the economic, as shown by the keeping quality of the 

 milk, and 



2. the hygienic, as shown by its possibility to spread dis- 

 ease, it is highly important that means should be adopted, 

 if possible, that will result in improving the keeping qual- 

 ity so as to diminish these losses, and at the same time in- 

 sure freedom from bacteria capable of developing disease. 

 Inasmuch as the fermentative changes which ordinarily 

 occur, and which lessen the commercial life of the milk as 

 a food, depend entirely on the development of living or- 

 ganisms that may find their way into the milk, an improve- 

 ment in the condition of the milk may be secured (1) by 

 excluding bacterial life so far as practicable, at the time 



