PROSPECTS FOR A NATURAL SYSTEM OF CLASSIFICATION OF BACTERIA 



other species, because here the pigment fulfils a fundamental metabolic 

 function, Sp. rubrum being a typical purple bacterium. A documen- 

 tation of this insight is in this case quite superfluous since this opinion 

 is fully shared by Bergey et al. as is proved by the fact that we meet 

 with the same organism again in an entirely different order (!) as 

 Rhodospirillum rubrum (Esmarch) Molisch. 



The next family, Bacteriaceae, offers no end of examples of heterogen- 

 eity, arbitrariness, utilitarianism, and disregard for natural relation- 

 ship. The subdivision of this family into its twelve tribes has obviously 

 been dictated by the tendency to keep apart the bacteria of importance 

 to the hygienist from all others. In the key to the tribes this is obtained 

 by giving the attribute 'pathogenic for animals' to the representatives 

 of the former group. This leads to the remarkable situation that in 

 this group of 'pathogens' several utterly harmless organisms, like 

 many Aerobacter and Alcaligenes species, are encountered. Apart from 

 this lack in consistency, making the organisms in question fully in- 

 determinable, no bacteriologist who isolates a bacterium from soil, 

 water, dairy products etc. will ever be able to decide whether it belongs 

 to the 'would-be pathogens' of Bergey et al.. Hence another group of 

 organisms, like the Escherichia species, becomes in most cases also 

 indeterminable. The attempt to reinforce the antithesis pathogenic- 

 non-pathogenic by ascribing to the former group an optimum tem- 

 perature of 37.5 °C, against one of 30 °C or less to the latter group, 

 shows the same lack of consistency as regards its practical application. 

 Numerous are the instances in which species with low temperature 

 optima are found in the so-called pathogenic group, whereas the 

 authors also do not hesitate to include bacteria with a temperature 

 optimum of 37 °C or even higher [Serratia spec, Lactobacillus spec.) 

 in the saprophytic group. Moreover in the species diagnosis several 

 organisms of this group are reported to be pathogenic or having the 

 intestinal canal as their normal habitat! 



If one now proceeds to the subdivision of the large group of sapro- 

 phytes or plant parasites one is struck by the miscellany of characters 

 which are used in the demarcation of the various tribes. One semi- 

 morphological property, the outcome of the Gram-stain, is used ; the 

 other characteristics are all physiological and of a very dubious nature, 

 such as the ability to grow either well or poorly on ordinary media, 

 the ability to digest cellulose or not, etc. Attention should be drawn 



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