Variations in the Virulence of Different Strains of Bacillus diptheriae

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Abstract
The occurrence of non-virulent strains of bacilli, which are indistinguishable except by animal experiment from virulent diphtheria bacilli, makes it especially interesting to investigate the varying pathogenicity of this bacillus. Owing to their complete lack of pathogenicity for laboratory animals, the exact relationship of the non-virulent types of B. diphtheriae to the virulent forms of this organism, cannot yet be considered as settled, although Arkwright (1910) has succeeded in obtaining a slight but very definite development of antitoxin in the blood of a horse immunised with non-virulent strains.