Pneumococcus Variants Intermediate between the S and R Forms

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Abstract
5 intermediate variants between types I-S and I-R pneumococcus were detected, viz., a, b, c, d, and e, by growing I-S pneumococci in homologous immune serum broth. They progressively appeared and disappeared in serial cultures. 2 of these, I-b and I-c, were easily stabilized in pure culture. The intermediates between S and R show a progressive and orderly change in agglutination reactions in homologous and heterologous immune sera. They also show progressive loss in virulence for white mice. Only 1 intermediate, II-c, was derived from type II-S. It was easily stabilized and is comparable to I-c in agglutination reactions and virulence. These observations indicate that dissociation of S pneumococci by growth in homologous immune serum is not a simple S[forward arrow]R change, but that a considerable number of intermediate variants with fairly well defined characteristics appear and disappear during the process.