CHAPTER III 

 THE CLASSIflCATIOX OF BACTERIA 



I. THE POSITION OF BACTERIA IN THE CLASSIFICATION OF 

 ORGANIC FORMS 



Bacteria occupy a unique place in the classification of organic 

 forms. The early view that bacteria were animal structures is 

 no longer seriously held, since their relation to plant forms is so 

 much closer as to leave no further doubt as to their claim to a 

 position in the vegetable kingdom. Their evident relationship 

 to both plants and animals places them, however, on the border 

 between certain forms clearly on one side or the other. In 

 certain respects bacteria are related to the Flagellata. Here 

 the organism consists of a protoplasmic body surrounded by a 

 thin cuticle, and provided with elongated appendages or flagella. 

 The protoplasm contains a nucleus and a pulsating vacuole. 

 The organism multiplies by the fission of the parent and by the 

 endogenous formation of resting bodies or cysts. The main 

 difference between the Flagellata and the bacteria lies in the 

 character of the membrane. In the former it is continuous with 

 the plasma, differing only in its physical structure ; while in the 

 bacteria the capsule, as seen in the phenomena of .plasmolysis, 

 is a distinct structure, separable from the central body. 



In the Flagellata, furthermore, the flagella are definite in 

 number in the different species, while in the bacteria their num- 

 ber is variable, especially when peritrichic. The Flagellata also 

 contain a distinct nucleus and vacuole, which is not certainly 

 the case in any of the bacteria. There is, therefore, little reason 



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