254 AGRICULTURE ON THE PACIFIC SLOPE 



shine is so necessary in our homes. We shall not 

 expect so much growth in this tumbler. Keep another 

 in the dark, but be sure to have it as warm as the one 

 in the light. A good way is to cover it with black 

 cloth or with a small box, and set it in the light 

 to keep it warm. Note whether there is more growth 

 in this. 



Put another on a cake of ice in a box, and cover it 

 with sawdust or keep it in a refrigerator. Refrigerators 

 are used to keep food from decaying, because the 

 bacteria cannot grow rapidly when they are kept cold. 

 But the cold does not kill them, and so we should not 

 put ice into our drinking water, because the ice may 

 contain living bacteria of the sorts which cause disease. 

 We should put the ice around the pitcher which holds 

 the water, but not into the water itself. 



Disinfection. Poisons are often used to kill bacteria. 

 Such a poison is called a germicide. We call the process 

 disinfection. Formalin is one of the best germicides, 

 and we may put a drop of this into the fourth tumbler 

 (or vial). It may not prevent the growth of the bacteria 

 at the bottom of the gelatin, because it may not be 

 able to reach them. This shows us how necessary it is 

 to disinfect a cut or wound by washin^every part of 

 it thoroughly with the germicide. The best way is to 

 use a medicine dropper and force a stream of the germi- 

 cide into the cut; in this way we can cleanse every 

 part of it without pain. If we then dust powdere^L 



