206 BACTERIA, YEASTS, AND MOLDS 



ruined for all practical purposes. There is no special rea- 

 son for believing that such milk is unwholesome ; but 

 people will not drink it since it is not normal milk. Milk 

 occasionally undergoes a sort of putrefaction, becoming 

 tainted in smell and taste. Sometimes it becomes blue 

 or red, and occasionally other changes take place in it. 

 Practically all of these phenomena are due to different 

 species of bacteria, and they may all be prevented if the 

 growth of the microorganisms can be held in check. 

 None of them, however, produce so much trouble in the 

 household as souring, and although, from the standpoint 

 of health, some of these other types of bacterial action 

 are more serious than the souring, the latter is the phe- 

 nomenon which produces the greatest inconvenience. 



Preservation of Milk 



The preservation of milk, which commonly means pre- 

 venting the milk from souring within too short a time, is 

 accomplished only by checking the growth of bacteria. 

 In considering the question of furnishing the household 

 with good, sweet, wholesome milk, several factors are 

 involved which must be considered separately. 



I. Source. Every housewife should be very particular 

 about the source from which she obtains her milk. This 

 is a matter frequently overlooked, and milk is obtained 

 without special consideration as to its source, upon the 

 general assumption that all milk is alike and that it makes 

 little difference from whence it comes. This is common 

 in the families of the rich and the poor, because the 

 former leave the purchase to servants, and the latter are 



