PROSPECTS FOR A NATURAL SYSTEM OF CLASSIFICATION OF BACTERIA 



in this family several large groups of bacteria not possessing the diag- 

 nostic characters of the family [Thiobacillus species, purple sulphur 

 bacteria, the coccoid iron bacteria described by Molisch, etc.) there 

 is no doubt that the recognized genera: Beggiatoa, Leptothrix, Creno- 

 thrix, Cladothrix and Thiothrix show neither affinities to the remaining 

 genera of the Schizomycetales nor to one another. 



It is clearly evident that in proposing this family Lehmann and 

 Neumann have more or less unconsciously used physiological char- 

 acters. Obviously the main reason for uniting the organisms in question 

 into one family is not so much their morphological similarity as the 

 peculiarity of their metabolism. 



The most outstanding contribution of the system of the German 

 authors and the one which has found general recognition is undoubt- 

 edly the realization of the close affinities existing between the genuine 

 Actinomycetes and the genera Corynebacterium and Mycobacterium. 



A revolution in the principles of bacterial taxonomy was brought 

 about in the years 1908 and 1909 by the appearance of Orla-Jensen's 

 publications [1908, 1909]. For the first time the classification of the 

 bacteria was based mainly on the physiological characters. The idea 

 underlying the proposed system is a phylogenetic one. A genealogy is 

 developed as a result of considerations concerning the succession of 

 physiological types in the course of the evolution of life on earth. 



Migula's influence is observable in the emphasis placed on the signi- 

 ficance of the difference in flagellation. The mode of insertion of the 

 locomotive organs is used for the separation of the bacteria into two 

 orders: the Cephalotrichinae and the Peritrichinae. A place was assigned 

 to the immotile bacteria in either one of these orders on the basis of 

 their physiological relationship to motile species. 



Orla-Jensen [192 1] has returned to the subject in a paper in which 

 he makes another eloquent plea for his main theses. With the exception 

 of a few minor amendments the system as proposed in 1908 is main- 

 tained. 



The system has the great merit that it is built upon a sound evalua- 

 tion of what is fundamental in the various physiological characters as 

 manifested by the value attached to the energetically important 

 katabolic properties. Another meritorious feature of Orla-Jensen's 

 system is the creation of several new genera for physiologically well 

 defined groups, together with the introduction of a rational code of 



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