STUDIES ON SAPROPHYTIC MYCOBACTERIA AND CORYNEBACTERIA. By H. L. Jensen, Macleay Bacteriologist to the Society. (Plates i-ii; seven Text-figures.) [Read 28th March, 1934.] Introduction. The genera Mycobacterium and Gorynebacterium were introduced by Lehmann and Neumann in 1896 and had as type species, respectively, the tubercle bacillus, Myc. tuberculosis, and the diphtheria bacillus, Cor. diphtheriae, two important pathogens which, together with a few related forms, distinguished themselves from all other bacteria known at that period by their characteristic morphology. Since then, numerous saprophytic and parasitic species have been added to the two genera. In Lehmann and Neumann's classical definition, Mycobacterium was distinguished by its formation of slender, frequently branched rods of irregular length, after staining with hot carbol-fuchsin not easily decolorized by treatment with mineral acids ("acid-fast"), and Gorynebacterium by its tendency to form cells of irregular thickness, club-or wedge-shaped, sometimes branched, not acid-fast, but often showing an irregular bar-or belt-staining. Because of the branching, Lehmann and Neumann regarded the two genera as closely related to the actinomycetes, from which they are distinguished by the lack of a typical mycelium (cf. Miehe, 1909; Haag, 1927). Lehmann and Neumann's definitions have in all essential points been adopted in subsequent treatises upon these organisms, for instance, Andrews, Bullock et al. (1923), Bergey (1923-30), Haag (1927), but the distinction between the two genera is by no means simple, as the following survey of their general morphology and biology will show. 1. Cell Morphology.— -The names Gorynebacterium and Mycobacterium were designed to indicate a prevalence of club-shaped cells in the former genus, and a tendency to branching in the latter. It is generally conceded that the typical clubs are as a rule, but not constantly, present in Cor. diphtheriae, but mostly absent in the non-virulent "diphtheroids" (Andrews, Bullock et al., 1923; Gins and Fortner, 1926; Kliewe, 1927). In older cultures of corynebacteria there is often an abundance of very big, spherical to lemon-shaped cells almost as big as yeast cells (Dale, 1910; de Negri, 1916; Bergstrand, 1918-23; Mellon, 1920-26; Brown and Orcutt, 1920; Grasset and Grasset, 1930), or smaller round cells appearing like true cocci (Madsen, 1896; Mellon, 1917-26; de Negri, 1916; Walker and Adkinson, 1917; Andrews, Bullock et al., 1923); these coccoid forms can be made entirely predominant by special methods of cultivation (Smirnow, 1908; Malchereck, 1932; Pope and Pinfield, 1932). Mycobacteria do not produce clubs in young, but sometimes in old cultures (Metschnikoff, 1888; Rabinowitsch, 1897;
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