CHAPTER III 



HOW THE BACTERIA ARE STUDIED 



IF you take a small wisp of hay, put it in 

 an open jar, and, covering it with water, 

 set it in a warm place for a day or two, you 

 will presently see that the water which was at 

 first perfectly clear, begins to get turbid, and, 

 after a while, a grayish scum collects on the 

 top. Now the water begins to give off a dis- 

 agreeable odor of decay. This is what has 

 happened: The bacteria of various forms, 

 which, in the dried condition, were clinging to 

 the hay, or which were in the water, have mul- 

 tiplied to such an extent that they made the 

 water turbid, and many of the mobile forms 

 have sought the surface, where the oxygen 

 was most abundant. The solution of or- 

 ganic material from the hay has furnished 



an abundance of food, and as the bacteria 



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