SELECTED PAPERS 



A further striking feature of the table is undoubtedly the occurrence 

 of an obligatory oxidative metabolism in nearly all morphological 

 types. Although this is partly due to the fact that in the present state 

 of our knowledge it is impossible to carry through a subdivision of the 

 aerobic metabolism into different types in a way comparable with 

 that which has been applied in the case of fermentative metabolism, 

 yet the table suggests that in the group of the obligatory oxidative 

 heterotrophic bacteria the main morphological evolution has occurred. 

 In this line of thought the physiological evolution will have taken 

 place in the different stages of this primary development. In this con- 

 nexion it must be remembered that in several cases the fermentative 

 metabolism is only a supplement to the oxidative mode of life. The 

 assumption made would also account for the more or less haphazard 

 distribution of the various katabolic types in the different morphologi- 

 cal units. 



A few words remain to be said with regard to the distribution of the 

 Gram-positive and Gram-negative genera in the system. As has been 

 remarked before we attach sufficient importance to this character to 

 require that a genus be homogeneous in this respect. Yet it appears 

 that the system given does not result in a clear-cut separation of the 

 Gram-positive and the Gram-negative genera. For the family of the 

 Micrococcaceae this differentiation has already been remarked upon. In 

 the family of the Pseudomonadaceae Gram-negative genera are strongly 

 predominant, whereas on the contrary in the family of the Mycobac- 

 teriaceae only Gram-positive organisms are encountered. Finally it does 

 not seem excluded that in the family of the Bacteriaceae a parallel devel- 

 opment has taken place in both Gram-positive and Gram-negative 

 forms. If the reported occurrence of Gram-negative Bacillus species 

 should be confirmed a division of this genus will become inevitable 

 which might lead to a clarification of the affinities in the family as a 

 whole. 



It will not have escaped attention that in the foregoing most 'bacte- 

 ria' which, already in previous systems, have been separated from the 

 so-called Eubacteriales have been left out of consideration. This holds 

 for the Spirochaetales, the Afyxobacterial.es, the Actinomycetales (p.p.) and 

 the Chlamydobacteriales. The Thiobacteriales in the sense of Buchanan 

 have been included with the exception of the genera Beggiatoa, Thio- 

 thrix and Thioploca. The representatives of the latter genera show such 



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