Conditions Influencing the Degree of Tolerance of Mouse Tumors in Rats Pretreated with Mouse Tissue

Grafts of the mouse mammary carcinoma of the RIII strain (M.M.C.) can result in tumors in 100 per cent and kill 50-100 per cent of rats pretreated at a suitable age with suitable doses of lyophilized mouse tumors or some normal mouse tissues of mice of the RIII strain. The pretreatment of older animals, or of young animals with lower doses, results in a weaker ef fect, characterized by a lower percentage of takes and smaller, regressing tumors. There is a limit to the age and to the dose beyond which the pre treatment produces no effect. The M.M.C, will grow in adult rats, provided the treatment was started early enough. The M.M.C, and Sarcoma 37 will grow equally well in rats pretreated with lyophilized prepara tions of either of these tumors. Pretreatment with tumor or normal tissue of species other than the mouse produces no effect. The M.M.C, can grow progressively in rats pretreated with tissues of mice belonging to strains in which the M.M.C, does not grow. Rats of two sublines of an inbred strain differed conspicuously in their response to treatment.