102 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



a similar classification of the bacteria is out of the question? The answer must 

 be obvious to those who recognize in the former an increasingly successful attempt 

 at reconstructing a phylogenetic history of the higher plants and animals, based 

 on comparative-anatomical, embryological, distributional, ecological, and paleon- 

 tological studies and who feel that comparable efforts in the realm of the bacteria 

 (and bluegreen algae) are doomed to failure because it does not appear likely 

 that criteria of truly phylogenetic significance can be devised for these organisms. 

 Forty-five years ago Orla- Jensen (1909) believed that it was possible to formu- 

 late an acceptable phylogeny of the bacteria by means of physiological-biochemical 

 considerations. But it has since been shown that there are compelling reasons 

 for doubting the validity of Orla- Jensen's premises (Oparin, 1938; van Niel, 

 1946; 1949a). 



Nevertheless, systems of classification of these organisms, complete with 

 genera, families, and orders have been developed in the course of the past century; 

 they have become more and more elaborate and complicated, and seem to be taken 

 seriously in at least some quarters. The simplest explanation for this attitude is 

 that classifying organisms in this manner has become an accepted habit, so 

 ingrained that one just kept on doing it, to paraphrase the last verse of Paul 

 Geraldy's "Meditation"^ : 



On prend I'habitude, vite, 

 d'echanger de petits mots. 



Quand on a longtenips dit les memes, 

 on les redit sans y penser. 

 Et alors, mon Dieu, Ton aime 

 parce qu'on a commence. 



When Cohn (1872) first proposed his six bacterial genera he was, however, 

 quite explicit in stating that these units did not have any phylogenetic signifi- 

 cance. They were simply "form-genera," providing descriptive names for groups 

 of bacteria possessing similar shapes. Though useless as guides to "natural rela- 

 tionships," these categories greatly facilitated the naming and identification of 

 bacteria. Once a newly isolated culture had been characterized as composed of 

 short rods, for example, it was thereby fixed as a Bacterium species, and the 

 establishment of its possible identity with earlier described bacteria could be 

 restricted to a comparison with the known members of this genus. 



Cohn subsequently (1875) expanded his system considerably, integrating the 

 ( form- ) genera of the bluegreen algae with those of the bacteria as components 

 of the class or family of the Schizomycetes. With further increase in our knowl- 

 edge of these microorganisms, owing largely to advances in microscopic tech- 

 niques, additional differential properties were discovered. Incorporation of such 

 characteristics in the descriptions consequently led to modifications of the diag- 

 nosis of several genera, and to the proposal of many new ones. During this period 

 a number of more or less "private" systems of classification were developed, such 

 as those of Zopf, Marpmann, de Bary, Fischer, Lehmann and Neumann, Migula, 

 Kruse, Orla-Jensen, and Chester, each one commanding a certain number of 

 adherents, with the result that various authors might refer to one and the same 

 organism by several different names. An extensive study of this somewhat con- 



1. Paul Geraldy, Toi et Moi, Paris: Stock, 1922. 



