Four transplantable mammary tumors of the mouse were subjected to freezing at −79° C., following the technic of Mann, for varying periods of time. Two of these failed to elicit progressively growing tumors in test mice.

Mammary tumor L 1221, which contains the milk agent, produced progressively growing tumors in C3Hb and in RIL/C3Hb F1 hybrid mice following inoculation of tumor mince. No growths appeared following intraperitoneal transfer.

Mammary tumor MT-8, known not to contain the mammary tumor milk agent, also produced progressively growing tumors at the site of inoculation in C3Hb and in RIL/C3Hb F1 hybrid mice following inoculation of the thawed tumor mince. Tumors were not produced in RIL strain mice. All intraperitoneal inoculations produced massive growths.

Each tumor was tested periodically, following initial growth in an F1 hybrid, for its ability to grow in mice of C3Hb and RIL strains and in RIL/C3Hb F1 hybrids. Progressively growing tumors were obtained in both C3Hb and RIL/C3Hb F1 hybrid mice but not in RIL strain mice.

These results are interpreted to mean that: (a) The “active” form of the mammary tumor milk agent is not the causative agent in producing tumors following inoculation of frozen tumor mince.

These results are interpreted to mean that:

  • The “active” form of the mammary tumor milk agent is not the causative agent in producing tumors following inoculation of frozen tumor mince.

  • There was found to be no evidence of “selective infectivity” of the milk agent in the experiments reported here.

  • Living tumor cells were actually transferred. The transplantation characteristics for both mammary tumors used in this study were those expected of strain C3H tumors, the strain of origin, and not those expected of tumors induced in F1 hybrid mice by an “active” agent.

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