NOMENCLATURE 315 



Apart from the increasing importance of antigenic analysis in the classification 

 of bacteria, it may be noted that there is a growing tendency to enlarge the range 

 of criteria employed in the differentiation of types and species, and to rely less 

 exclusively on the somewhat crude series of fermentation reactions that played 

 so large a part in earlier systematic studies. The reaction of an organism to varia- 

 tions in the partial pressure of carbon dioxide, its resistance to various dyes, its 

 tolerance of a high concentration of hydrogen-ions, all these and many other 

 criteria are being increasingly employed in defining bacterial groups, and in tracing 

 the relation of one group to another. 



There is one criterion commonly employed whose use, we believe, should be 

 discontinued, from both the formal and the utilitarian standpoint, namely, the 

 ecological. The relationship of an organism in its natural state to other forms 

 of life in its environment is conditioned by many other factors besides those inherent 

 in its own protoplasm ; and in the absence of knowledge about those factors, 

 we cannot say what features of the habitat of an organism are necessarily con- 

 nected with it. Consequently, habitat is on a priori grounds likely to be mis- 

 leading as a diiferential character. It will be even more misleading on utilitarian 

 grounds, since we classify bacteria in order to make precise bacteriological explora- 

 tions of our environment. If, then, the definition of a species includes habitat 

 in a given type of environment, we may delay its recognition in another equally 

 important environment. It is, for example, only recently that the probable 

 identity of Phytomonas polycolor, a tobacco-plant pathogen, and Ps. pyocyanea, 

 an organism infecting wounds in war, has been recognized (Elrod and Braun 

 1941). 



One essential character of any systematic nomenclature is stability ; and 

 those who have to read or write about bacteria at the present time are in a singularly 

 unhappy position in this respect. When the same organism is masquerading as 

 Bacillus typhosus, Bacterium typhosum. Salmonella typhi or Eherthella typhi, while 

 another answers with equal readiness to the names of Micrococcus melitensis, 

 Bacillus melitensis. Brucella melitensis or Alkaligenes melitensis, all printed in 

 italics with a capital letter to the generic name, the student, or even the more 

 practised reader of bacteriological literature, may be excused some degree of 

 confusion. 



It would, perhaps, be simplest to await some agreed solution of our difficulties, 

 and use the moribund nomenclature which was current before the first world war, 

 till some better system with authoritative support is offered in its stead. There 

 are, however, real disadvantages in such a course. It is desirable, especially 

 from the student's point of view, that a name should be as informative as pos- 

 sible. The scientific name of a living organism should tell us as much as possible 

 about that organism itself, and about its relation to other organisms with different 

 names. The latter problem is the particular concern of the systematist ; and 

 it may be many years before we know enough about the relationship of bacteria 

 to evolve a system of classification in which those relationships can be adequately 

 expressed. It is, however, possible to allot names to bacterial groups, which will 

 give us a considerable amount of information with regard to the species, races, 

 or types, of which they are constituted. In this respect the conventional bac- 

 teriological nomenclature of the past fifty years has been a conspicuous failure. 

 Nothing could be less informative than the name Bacillus, when that name is 

 applied to any rod-shaped bacterium ; and the student, who has memorized the 



