Freshly isolated strains of meningococci present a number of characteristics which can be shown to differ not inconsiderably from those of stock strains long maintained on artificial media. Rough variants of the different types can be demonstrated, either arising spontaneously in vivo or in vitro, or evoked in the laboratory by the method described by Enders. Neither the freshly isolated strains—which are smooth— nor, in most cases, the rough variants of them are stable, both showing a tendency to pass over into the stock form or variant. The stock strains in the course of transformation from the freshly isolated strains show changes in morphology and cultural characteristics, and in viability in defibrinated blood.

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