Studies were made of the effects of multiple sublethal doses of total-body X-irradiation (six weekly exposures of 200 R each) on the subsequent appearance of tumors in female mice fed either highly purified diets or a natural food stock ration. Six months after the first X-ray exposure, mice fed the purified diets showed a markedly higher incidence of a number of tumors (lymphosarcoma of the mandibular lymph nodes, lymphosarcoma of the thymus, uterine adenocarcinoma, Harderian gland adenocarcinoma, and others) over that of similarly X-irradiated mice fed the stock ration. Nonirradiated mice of similar age fed identical diets were virtually free of such tumors. The protective factor or factors in the natural food stock ration is apparently distinct from any of the known nutrients.


This investigation was supported in part by USPHS Research Grant #DE 02582-02 from the National Institute of Dental Research, NIH, Bethesda, Md.


Presented in part at the 59th Annual Meeting, American Association for Cancer Research, Atlantic City, N. J., April 11–13, 1968.

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