ATOMIC MEDICINE utes by exposure of the remaining half with shielding of the previously ex- posed portion (Swift ef al.). 9.7.6 Parabtosis. Parabiosis accomplished some time prior to irradiation (Huff et al.; Brecher and Cronkite; Finerty e¢ al.) markedly decreased mortality of animals exposed to an otherwise fatal dose of radiation. J fot setaepathTasasliysaline aril 299 The factors that modify the radiation response after irradiation can be divided into those that increase the mortality rate, and those that favorably influence the mortality rate and survival time. The former will be considered first. 9.8.1 Unfavorable Postirradiation Factors. Smith and Smith showed that moderate exercise only slightly decreased the survival rate of mice. Strenuous exercise in the form of forced swimming after irradiation in- creased the mortality rate strikingly in rats Cximmeldorf; Newry). Smith and Smith presented evidence showing that induction and maintenance of a hypermetabolic state by the administration of dinitrophenol after irradiation for the full observation period increased mortality. Anti-thyroid ther- EeMee aietad 9.8 Postradiation Factors rate. Eliinger reports that testosterone proprionate administered in daily doses of 0.25 and 0.5 mg. to mice after irradiation with an LD» increases the mortality rate. Smith ef al. concluded that ACTH and cortisone do not increase the survival rate and that ACTH after irradiation may be harmful. It appears that synkavit and other related compounds of the vitamin K group will increase the mortality of irradiated animals. The material tends to concentrate in some tumors following intravenous injection (Mitchell et al.). 9.8.2 Postradiation Factors that Increase the Survival Rate. In general, one ean divide postradiation modification of radiation injury into three general categories: (a} the strikirg and rapid restoration of severely damaged, hemepoictic tissues by shielding of bone marrowor spleen, parabiosis, injection of bone marrow, or splenic homogenate, etc., which are effective following usually lethal doses of irradiation from which spontaneous re- covery is rare; (b) the less striking effect of postradiation stimulation of myelopoiezis and erythropoiesis. Myelopoiesis can be stimulated by sterile inflammation (Cronkite and Brecher) in the midjethal or sublethal, but not in the absolute lethal zone. Erythropoiesis is stimulated by anoxic stimull or by normal anemic plasma in the sublethal range only; (¢} modification of the histological and clinical picture by substitution (red cell, white cell, and platelet transfusion with or without use of antibiotics) with moderately increased survival rate or induced restoration of hemopoietic tissues (Sorensen ef al.). The last category simply represents sub- ns RORRSMETaetnttutiaoaSIe es, ct atiyt Ra PEELMeee apy with thiouracil and propyl-thiouracil did not influence the mortality