The V2 carcinoma—a transplanted rabbit cancer derived originally from a virus-induced papilloma and carrying in masked or altered form the virus primarily responsible for it—was propagated in five successive groups of animals all previously hyperimmunized against the papilloma virus. The cancer grew as well in the hyperimmunized hosts as in normal animals implanted during the same months; and serological tests, made when the tumor was eventually returned to ordinary hosts, proved that the virus was still associated with the carcinoma cells: it had increased to the usual extent as the tumor grew in the hyperimmune animals.

The continued increase of the neoplastic virus during propagation of the V2 carcinoma in hyperimmunized hosts contrasts sharply with the elimination of certain extraneous passenger viruses when the tumors they ride upon are grown in hosts previously immunized against them. The facts as a whole would seem to warrant a distinction between the enduring partnership of a neoplastic virus and carcinoma cells on the one hand and the casual association of passenger viruses with tumor cells on the other.

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