14 GENERAL MORPHOLOGY AND BIOLOGY. 



The Classification of Bacteria. There have been 

 numerous schemes set forth for the classification of bac- 

 teria, the fundamental principle running through all of 

 which has been the recognition of the two sub-groups and 

 the type forms mentioned in the opening paragraph above. 

 In the attempts to still further subdivide the group, 

 scarcely two systematists are agreed as to the characters on 

 which sub-classes are to be based. Thus De Bary divides 

 bacteria according as they are endosporous or arthrosporous, 

 and this, along with the planes in which division takes 

 place, constitutes the chief basis on which sub -classes 

 have rested. Other characters, such as presence or 

 absence of flagella, appearances of bacteria when grouped 

 together in masses, physiological and even patho- 

 genic properties, have been utilised by different authors 

 as means of classification. Our present knowledge of 

 the essential morphology and relations of the group is 

 as yet too limited for a really natural classification to 

 be attempted. To prepare for the elaboration of the 

 latter, Marshall Ward suggests that in every species 

 there should be studied the habitat, best food supply, 

 condition as to gaseous environment, range of growth, 

 temperature, morphology, and life history, special properties 

 and pathogenicity. 



We must thus be content with a provisional and incomplete 

 classification. We have said that the division into lower 

 and higher bacteria is recognised by all, though, as in every 

 other classification, there occur transitional forms. In sub- 

 dividing the bacteria further, the forms they assume consti- 

 tute at present the only practicable basis of classification. 

 The lower bacteria thus naturally fall into the three groups 

 mentioned, the cocci, bacilli, and spirilla, though the higher 

 are more difficult to deal with. Subsidiary, though im- 

 portant, points in still further subdivision are the planes in 

 which fission takes place and the presence or absence of 

 spores. The recognition of actual species is often a matter 

 of great difficulty. The points to be observed in this will 

 be discussed later (p. 109). 



