214 BACTERIA, YEASTS, AND MOLDS 



of a household. While a few years ago there were dairies 

 that did this, to-day the plan has been abandoned except for 

 certain forms of milk put up in cans, like unsweetened con- 

 densed milk. Such high heat makes decided chemical changes 

 in the milk which lower its food value. 



A far more common method is simply to boil the milk. 

 While this temperature does not kill all bacteria, still it has 

 been quite common to speak of it as sterilizing. In hot 

 weather milk is very often boiled to prevent its souring, and 

 in some European countries milk is never drunk without 

 boiling. 



The purpose of sterilization is twofold, (i) It delays 

 the souring of the milk. Milk that has been boiled may 

 keep from souring for several days, whereas without boiling 

 it will keep only a few hours. With the poorer families in 

 cities this is the chief purpose of boiling the milk, since it 

 will not keep more than a few hours without ice, and they 

 have no ice chests where it can be preserved from souring. 

 (2) The destruction of disease germs. Milk is a common 

 means by which certain contagious diseases are distributed 

 through a community. The diseases in question are pro- 

 duced by bacteria in the milk, and boiling destroys them. 

 This is the ground upon which physicians and health boards 

 have in the past so widely advocated the boiling of milk 

 that is to be used for drinking. Since boiling does destroy 

 practically all the disease germs liable to be in milk, it 

 makes it incapable of distributing contagious diseases. 



There are certain disadvantages in boiling milk. The 

 taste is wholly changed, for boiled milk is quite a different 

 article from raw milk. Most people do not enjoy the taste 

 of boiled milk, and the adoption of sterilizing or boiling 



