BACTERIA 257 



floors covered with rugs which may be easily taken up 

 and cleaned. 



Are there bacteria in water? We will now test our 

 drinking water for bacteria. Put one of the flat bottles 

 (figure 153) into warm water until the gelatin is melted. 

 Then take a piece of wire, bend the end into a small 

 loop, pass it once or twice through a flame to kill any 

 bacteria which may be on it, and dip it into the drinking 

 water so as to take up a large drop. Put this drop in 

 the bottle, shake it a little to mix it with the gelatin, 

 put the cotton back into the neck of the bottle, and place 

 the bottle on its side as shown in figure 153. Every 

 one of the bacteria in the drop will grow and make a 

 spot in the gelatin; by counting these spots we can tell 

 how many bacteria were in the drop. Every city has a 

 law which says that the milk or drinking water should 

 not contain more than a certain number of bacteria. 

 The bacteria are counted in the way just described. 

 Test your milk supply in this way and also the bottled 

 water, especially distilled water which is on sale. It 

 often happens that such water has many bacteria in it, 

 because the bottles are not kept clean. Bottled soda 

 water or ginger ale is safe, because the carbonic acid 

 kills the bacteria; this is a good thing to remember 

 when traveling. Never drink from the water tank on 

 a railway train or other public place if you can help it. 

 Get fruit or bottled soda water or ginger ale, instead. 

 Never use a public drinking cup; carry your own cup 



