Variability in the Diphtheria Group of Bacilli

One of the most interesting questions in bacteriology at present is that of the mutual relationship borne by the organisms in the socalled " groups." In the case of the diphtheria group the problem is of particular importance because of its bearing on public health service methods, as these naturally must differ in many respects if the group consists of two or more distinct species instead of but one comprised of several types. The overwhelming majority of bacteriologists at present look upon the group as consisting of at least three definite species, B. diphtheriae (Klebs-Loffler1), B. pseudodiphthericus (Hofmann-Wellenhof2), and B. xerosis (Kuschbert and Neisser3), while opinion is divided in regard to the numerous other types, collectively known as diphtheroids, of which the most important are B. coryzae segmentosus (Cautley4), B. diphtheroides (Klein5), B. clavatus (Kruse and Pasquale6), B. septatus (Gelpke7), and Corynebacterium lymphae vaccinae (Levy and Fickler8). Some investigators consider all these forms as varieties of either B. pseudodiphthericus or B. xerosis, while others make separate species of some or all. On the other hand, Roux and Yersin9 and, more recently, Behring10 look upon the diphtheria group as hut a single species, regarding the morphological and biological differences between the types as insufficient to justify establishing new species. Their views, however, have found few adherents. The important features of typical examples of the three main forms may be summarized as follows: Morphology.