220 BACTERIA, YtASTS, AND MOLDS 



It is true that such milk may keep for two days without 

 difficulty, but bacteria are growing in it all the while ; and 

 although the milk does not sour, it soon becomes unfit to 

 drink. Hence pasteurized milk must be used quickly, — at 

 least within twenty-four hours from the time when it was 

 pasteurized, — and meantime it should be kept cool just 

 as if it had not been pasteurized. 



The most important rule in regard to the use of milk in 

 the household is that it should be used fresh. No method 

 of keeping it can prevent all bacteria from growing, and 

 although the use of refrigeration, pasteurization, or steriliza- 

 tion may keep it in a drinkable condition for a day, two days, 

 or even longer, it is always open to suspicion after it has 

 been kept for this length of time. Milk is plenty old enough 

 by the time it reaches the house, and it should therefore 

 always be used fresh. It is far better to obtain it frequently, 

 in small quantities, using it up as soon as possible after it 

 reaches the home. 



Preservation of Eggs 



Eggs prove to be particularly difficult to preserve. They 

 are sure to contain bacteria inside the shell, deposited there 

 before the egg was laid. These will in time cause the egg 

 to spoil. Eggs cannot be sterilized by heat, for this cooks 

 them. Drying, of course, alters their nature. The use of 

 low temperatures will preserve eggs as well as fruit. They 

 may be protected from actual spoiling for some time by 

 placing them in certain liquids that keep away the air. Brine 

 is used, and water glass is even more successful. To use 

 the latter, mix the water glass purchased at the drug store 



