CHAPTER III. 



HOW THE BACTERIA ARE STUDIED. 



IF you take a small whisp 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 organic 

 material from the hay has furnished an 

 abundance of food, and as the bacteria 

 have torn this into simpler forms to get the 



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