CHAPTER XVIII 



BACTERIA 



IT used to be thought that everything decays natu- 

 rally sooner or later, and that this cannot be helped. 



But we now know that 

 decay is caused by very 

 small plants (called bac- 

 teria), and that if they 

 can be kept away or 

 killed, decay will not 

 take place. 



How to sterilize. One 

 way to kill these tiny 

 plants is to steam or boil 

 them. To test this we 

 may slice a potato and 

 put a slice into each of 



FIG. 150. -Tumbler containing a slice anum berof Small bottles 

 of potato covered with cotton held 



in place by a rubber band. Used for or tumblers, aS shown in 



growing bacteria. _, r ^ , 



figure 150. Over the 



top of each tumbler we put cotton wool and fasten it 

 with a rubber band; or we stuff the cotton into the top 

 of the tumbler or bottle as shown in figure 151. 



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