PROSPECTS FOR A NATURAL SYSTEM OF CLASSIFICATION OF BACTERIA 

 2. PRINCIPLES IN BACTERIAL CLASSIFICATION 



If one examines the various systems of bacteria proposed up till now, 

 it becomes evident that many of these systems are almost entirely the 

 outcome of purely utilitarian motives. Very often such artificial 

 systems are ultimately impractical because as a rule newly discovered 

 facts necessitate profound modifications or even the construction of 

 new systems at short intervals. 



Naturally, the only truly scientific foundation of classification is to 

 be found in an appreciation of the available facts from a phylogenetic 

 point of view. Only in this way can the natural interrelationships of 

 the various bacteria be properly understood. It has to be admitted at 

 once that, inasmuch as the course of phylogeny will always remain un- 

 known, the basis of a true phylogenetic system of classification will be 

 very unstable indeed. On the other hand it cannot be denied that the 

 studies in comparative morphology made by botanists and zoologists 

 have made phylogeny a reality. Under these circumstances it seems 

 appropriate to accept the phylogenetic principle also in bacteriological 

 classification. 



The question then arises in which characters phylogeny expresses 

 itself. There is no doubt that in this respect morphology remains the 

 first and most reliable guide. It is, however, a commonplace in system- 

 atic bacteriological literature to bewail the scantiness of suitable mor- 

 phological data. This, in turn, is chiefly responsible for the unsatis- 

 factory state of bacterial taxonomy. 



This situation has, already a long time ago, induced several authors 

 to apply characters of a physiological nature in addition. The first steps 

 in this direction were made timidly, but gradually the defenders of 

 the good right of a physiological basis for taxonomy have become more 

 and more numerous. 



It seems superfluous to dwell upon this evolution here. It may suffice 

 to remark that nowadays the indispensability of physiological char- 

 acters for the purpose of classification has been generally accepted, 

 which is only natural because, after all, these physiological differences 

 must be considered as expressions of variations in submicroscopical 

 morphology. 



In this connexion the predominant problem is only how the macro- 

 morphological and the micromorphological (physiological) characters 



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