Mice sensitized by an injection of 0.2 cc. of rat blood and 10 days later inoculated with a mixture of rat blood and a transplantable mouse cancer showed a high degree of immunity to the cancer growth, while mice sensitized in the same manner and inoculated with cancer graft with no rat blood showed no immunity. Likewise, non-sensitized mice inoculated with a mixture of rat blood and cancer cells showed no immunity.

Mice sensitized to rat blood and then given a series of doses of x-rays between the time of this injection and the inoculation of the cancer-rat blood mixture showed a suppression of the factors affording protection or immunity, since the cancers grew as well in these animals as in the controls.

Mice were sensitized with rat blood and 10 days later inoculated with a cancer-rat blood mixture. 20 hours after the inoculation when the cellular exudation was at its height, the cells were destroyed by a local dose of x-rays. The degree of immunity was reduced and the cancers grew almost as well as in the controls.

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