SELECTED PAPERS 



genus Vibrio, as already pointed out by Migula, is so unmistakable 

 that this amendment must be considered a decided improvement. 

 Following the order of the Eubacteriales we encounter the order of the 

 Rhodobacteriales comprising the natural group of the photosynthetic 

 purple bacteria in two suborders : the sulfur-containing and the sulfur- 

 free species. The merit of the demarcation of this order as compared 

 with that of the Thiobacteriales Buchanan is to be found in the fact that 

 the colourless sulfur bacteria of the genera Beggiatoa, Thiothrix and 

 Thioploca, which show so different natural affinities (colourless Cyano- 

 phyceae as rightly suggested by Pringsheim), are not mixed up with the 

 purple bacteria. Characteristic for Pringsheim's order of the Myco- 

 bacterials is that it is again restricted to the homogeneous group formed 

 by the genera Coryne bacterium, Mycobacterium and Actinomyces. Signifi- 

 cant for an appreciation of the clear insight of the author is his sug- 

 gestion that the rod-shaped lactic acid bacteria might also belong to 

 this order. The fifth order of the Desmobacteriales needs no comment 

 since Pringsheim himself stresses its provisional nature. 



From all the systems of classification based mainly on the morphol- 

 ogy of the organisms Pringsheim's scheme is the most satisfactory one, 

 and it compares especially favourably with Enderlein's [1925] revolu- 

 tionary attempt at classifying the bacteria according to principles of 

 comparative morphology and ontogeny ('cyclogeny'). This author 

 rejects all previous attempts at classification because they are not 

 based on a careful and thorough cytological study and from a theo- 

 retical standpoint his plea for attaching predominant importance to 

 cytological and ontogenetic characters is very convincing. However, 

 as pointed out earlier in this paper, our knowledge of characters of this 

 kind is necessarily extremely limited and Enderlein's own contribu- 

 tions in this field do not change this situation to any appreciable 

 extent. For it has escaped the attention of this zoologist that by far the 

 greater part of the cytological details reported by him are theoreti- 

 cally undetectable since the dimensions of the structures described are 

 below the limits of the resolving power of the microscope. This implies 

 that most of the 'life-cycles' which are at the basis of Enderlein's sys- 

 tem are fully artificial.* However tempting the classification outlined 

 may be at first sight (cf. e.g. the table on p. 236), its value must be 



* For sound ideas concerning the term 'life-cycle' the reader is referred to the 

 note by Ch.-E. A. Winslow, Science. 81, 314, 1935. 



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