Abstract
In a previous communication 1 a method was described for demonstrating the growth-inhibitory and bactericidal action of normal serum-leucocyte mixtures for the pneumococcus. Serum and washed leucocytes, contained in small tubes, were seeded with varying numbers of pneumococci. The tubes were then sealed with paraffine and attached to a specially devised apparatus which produced constant agitation during incubation. By means of this method, it was found that the growth of small numbers of pneumococci of low virulence, for cats, was markedly inhibited by the cat serum and leucocytes. On the other hand, small numbers of a strain virulent for rabbits, were able to grow in the rabbit serum-leucocyte mixtures.
By employing avirulent strains of pneumococci for rabbits and cats with the same method, a study has been made to determine the action of the pneumococcus soluble substance2,3,4 on the growth of such strains of pneumococci in the rabbit or cat serumleucocyte mixtures. It was found that whereas the growth of a small number of avirulent pneumococci was normally inhibited by such mixtures, the addition of a very small amount of the purified soluble substance of the homologous type was able to cause growth of the organisms in them. Such action of the soluble substance was shown to be highly specific to type. A type II substance assisted the growth of only type II pneumococcus, likewise a type III substance, the growth of type III pneumococcus only.
Experiments employing broth filtrates of young pneumococcus culltures in place of the purified soluble substances gave similar results, thereby esta'blished the identity of the purified substance with the substance originally described in the cultural fluids of pneumococcus cultures.
From the results of previous studies, such action of the pneurnococcus soluble substance may be interpreted as having the power of rendering an avirulent pneumococcus of the homologous type virulent.
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