CHAPTER XI 



THE RELATIONSHIP OF BACTERIA 



Introduction. The boundary between the animal and 

 vegetable kingdoms, if such there be, is not definite. There 

 has been much confusion in regard to the accurate differentia- 

 tion of these kingdoms since the time of the first records of mic- 

 roscopic life. The indications are that it will be some time before 

 scientists will definitely settle this problem and be able to state 

 in certain instances that a particular low form of life is a plant 

 or an animal. We refer, obviously, to those animal and plant 

 forms which are of the simplest structure and which closely 

 resemble each other physiologically and morphologically. 

 In all probability, according to recent investigations, this 

 problem will be greatly elucidated by the chemists who, on the 

 perfection of their technique, will find that the main differ- 

 ences between plants and animals are those of chemical 

 structure. 



The terms "animal" and "plant" were devised years ago 

 before the single-celled forms of life which possess similarities 

 to both groups were known. It is in a measure senseless to 

 try to apply these terms to organisms for which they were 

 never intended. The terms, as have been stated by various 

 writers, were intended to apply to such contrasts as oak trees 



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