390 ELEMENTARY BIOLOGY 



food very hot or very cold. We are not usually ready to cook 

 our food immediately ; meats and vegetables have to be kept 

 for longer or shorter periods before cooking as well as after 

 cooking. We therefore turn to the low temperature as an aid 

 in preserving food against the destructive action of bacteria. 

 Refrigeration has been the means of preventing great loss 

 through the decomposition of food, since at low temperatures 

 bacteria cannot multiply. We must be careful, however, not to 

 assume that well-preserved food from the refrigerator is neces- 

 sarily free from injurious microbes, since any organisms that 

 may have been present before the food was placed in the 

 refrigerator are still there and are still capable of growing and 

 multiplying when the suitable temperature is reached. It is 

 also necessary to keep refrigerators perfectly clean and free 

 from neglected food particles that may retain bacteria. This 

 principle applies, of course, to all cupboards, pantries, lunch 

 boxes, or other places in which food is kept temporarily or 

 permanently. 



Milk, soups, jellies, fruit juices, preserves, and similar food 

 preparations containing a great deal of water are exceptionally 

 favorable to the growth and multiplication of bacteria. They 

 are therefore especially subject to the decaying action of bac- 

 teria, and require special care in their handling and storing. 

 In making preserves of fruits or vegetables the chief precau- 

 tions are concerned with the destruction of the bacteria already 

 present in the materials used, and with the prevention of the 

 entrance of other bacteria. The first end is attained by 

 cooking the materials until the heat kills the germs. The 

 second is attained by placing the cooked material in perfectly 

 clean vessels that can be covered so as to exclude absolutely 

 all bacteria. 



432. Milk regulation. The regulations prepared by the 

 health authorities of cities and states for those who have to 

 handle milk take into consideration the importance of milk 

 for human beings, especially for children, and the ease with 



