FORM AND CLASSIFICATION OF BACTERIA. 17 



as budding. They are designated by the term blastomy- 

 cetes. 



A great many elaborate attempts have been made at 

 classifying- bacteria. Owing to their extremely minute size 

 it is, as a rule, impossible to follow out the life-history of 

 each individual species. The characteristic development 

 of the fruit-organs in higher plants affords a basis for a 

 natural classification whereby the various species are 

 grouped into genera and families. Such a classification is 

 natural, because it brings together the various individuals 

 which possess the same structure and development. Inas- 

 much as bacteria are unicellular it follows that they do not 

 possess definite fruit-organs, and owing to their size very 

 little indeed can be said of their structure. The various 

 classifications proposed are based upon characteristics such 

 as form, size, manner of division, presence of spores, 

 motion, number and arrangement of whips, etc. It is evi- 

 dent, therefore, that all such systems of classification are 

 more or less artificial. 



For practical purposes it is sufficient to divide bacteria 

 according to their external form into three groups. These 

 are: 



Micrococci, or spherical bacteria; 



Bacilli, or rod-like bacteria; 



Spirilla, or screw-shaped bacteria. 



c 



FIG. i. a Micrococcus; Bacillus; <: Spirillum. 



In a few instances special names are applied to certain 

 forms of one or another of these three primary types. 

 Thus, the term bacterium is occasionally applied to a very 

 short bacillus. It has the same significance as the word 



cocco-bacillus, which indicates that the organism may at 

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