CHAPTER 10 



THE CLASSIFICATION OF BACTERIA 



As has been indicated in preceding chapters, it is the behaviour rather than the 

 nature of bacteria which has interested the bacteriologist. It is not surprising, 

 therefore, to find that the field of systematic bacteriology has been very largely 

 neglected. The study of bacteria has indeed never passed through that phase of 

 detailed and accurate description, which has formed so important a part of the 

 foundations of botany and zoology. 



This neglect is not entirely attributable to lack of interest. In dealing with 

 the morphology of bacteria, we have pointed out the difficulties which are in- 

 herent in any study of bacterial structure. As a result of these difficulties, the 

 bacteriologist has come to rely very largely on physiological characters in the 

 differentiation of bacterial groups, and the study of the antigen-antibody reactions 

 has led to the elaboration of a technique which is peculiar to this field of biology. 

 In addition to these methods of studying bacteria in artificial culture, the medical 

 bacteriologist, who is primarily interested in the role of micro-organisms in disease, 

 has naturally developed the habit of testing the pathogenicity of the strains he 

 has isolated by the experimental infection of laboratory animals. 



Employing a combination of these methods, the bacteriologist has learned by 

 experience to identify a large number of well-difierentiated and stable bacterial 

 types ; and to these he has given names. The criteria that have determined 

 the classification and nomenclature of bacteria are not, therefore, such as would 

 be accepted by the systematist in any other branch of biology ; and the bac- 

 teriologist himself has not in general troubled overmuch as to the validity of a 

 system which has developed rather as the result of luck than of cunning. 



The inconvenience of a total absence of classification, reflected in a chaotic 

 nomenclature, has, however, been so great, that various attempts have been made 

 to introduce some sort of order into the bacteriological household. We cannot 

 here enter into any historical description of the various systems which have been 

 propounded ; except to note that a comparison of those suggested by Zopf (1885), 

 Migula (1894), Krvise (1896), Lehmann and Neumann (1896) and Orla-Jensen 

 (1909) will reveal how widely the lines of cleavage may differ, when a large 

 biological group is viewed from different angles. Those who desire more detailed 

 information on this aspect of the question are referred to the two reports of the 

 Committee of the Society of American Bacteriologists on characterization and 

 classification of bacterial types (1917, 1920) ; the monograph by Buchanan (1925) ; 

 the manual by Bergey and his colleagues (1939) ; and to a paper by Buchanan and 

 others (1928), which sets out in diagrammatic form the classifications suggested 

 by Migula, Orla-Jensen, Buchanan, Castellani and Chalmers (1920), Lehmann 



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