448 Our Surroundings 



the temperature must not be allowed to get below freezing, as 

 fruits are decomposed by freezing. Meats, however, including 

 fish and fowl, will be suitable for use for an indefinite time if kept 

 in a frozen condition, since freezing will prevent the development 

 of bacteria. Cold storage plants for preserving food material are 

 employed on a large scale by persons who expect to place it on 

 the market at a time when the food has become scarce. The 

 object, of course, is to sell the food for a higher price than it 

 brings when it is abundant. 



Other Devices for Preserving Food. Most well-appointed 

 homes have an ice chest or refrigerator. The ice chest will check 

 but not wholly stop the growth of bacteria, so food is not so 

 thoroughly protected as when in cold storage. Cool cellars are 

 usually found in most homes. In rural sections, deep wells are 

 often used as places in which to preserve food temporarily. Small 

 buildings containing cold running water are often employed and 

 are very useful and essential to the success of dairymen. 



Formerly, dealers in food used various chemical substances 

 to prevent food from spoiling. Often these were of a nature that 

 would be harmful to the health of those who ate food thus pre- 

 served. Since the passage of the Pure Food and Drugs Act by 

 the United States government the use of these substances has been 

 greatly lessened. 



When water evaporates it has a cooling effect. This method 

 may be used for keeping foods cool. Tents are sometimes used 

 in warm countries for storing perishable foods. They are placed 

 in such a position that the air can move about them readily. 

 Water is allowed to drip on the roof of the tent and run down 

 the sides. As it evaporates, the tent is cooled. If the relative 

 humidity is low, the cooling effect is very noticeable. 



Parasitic Bacteria. Parasitic bacteria are the most harmful 

 kind since they live on other organisms and often cause disease. 

 When they attack human beings they are popularly spoken of as 

 germs or microbes. Diseases caused by bacteria or other germs 

 are called communicable diseases. Among the most dreaded of 

 these diseases are tuberculosis, typhoid fever andxliphtheria. Their 

 bacteria flourish especially well where filthy conditions prevail, but 



