CHAPTER II 



BACTERIA AND SOME OF THE THINGS WHICH 

 THEY DO 



THERE are many very good reasons for 

 believing that when life first appeared 

 upon the earth it showed itself in a very sim- 

 ple and primitive form, in some such form 

 perhaps as we have seen in the amoeba or 

 other simple cells. But as the ages passed, in 

 accordance with the principles of the physio- 

 logical division of labor, which we have glanced 

 at in the last chapter, many of the living 

 beings gradually assumed more and more 

 complex forms and capacities. 



Not all living things, however, shared in 

 these evolutionary changes. There is, in fact, 

 a great group of lowly plants, so small as to 

 be quite invisible to the naked eye, and which 

 until within a few years have been entirely 



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