ATOMIC MEDICINE ticularly over the abdomen. However, the data that have been presented are not statistically conclusive. 9.7.4 Preradiation Factors that Increase the Survival Rate. In this section is included a discussion of a number of procedures and agents that must be ‘carried out or be present prior to and, or during actual exposure to radiation in order to afford protection. Perhaps the most widely known procedure is a lowering of oxygen tension, or hypoxia, first shown by Lacassagne in 1942. This finding has been confirmed extensively, and protection is afforded not only against carly effects (Limperos; Dowdy ef al.) but late effects as well (Lamson, Billings ef al.). Although hypoxia during irradiation is casily accomplished by means of exposure in an atmosphere containing little or no oxygen, a number of other procedures or agents that produce a lowering of oxygen tension in the tissues appear to protect eza this mechanism. Thus hypothermia protects presumably by virtue of the fact that it results in hypoxia. Carbon monoxide (Konecci, Taylor and Wilks) and cyanide (Bacq and Herve) are capable of increasing the survival rate. Agents that produce methemoglobinemia such as p-aminopropiophenane or PAPP (Storer and Coon) and nitrate (Cole, Bond and Fishler) are active. A variety of substances afford protection if injected prior to exposure, and Hektoen apparently was the first to report such protection in 1918 by the injection of foreign protein 10 days prior to irradiation. Fstradiol was shown to decrease mortality if injected 10 days before irradiation of mice (Treadwell, Gardner, and Lawrence; Patt ef al.). Interest in chemical preprotection was heightened in 1949 by the finding that SH-contaiing compounds such as cysteine (Patt) and glutathione (Cronkite ef al.) yield considerable protection. The list of compounds that afford some degree of protection has grown steadily, and the subject has been reviewed extensively (Alexander and Bacq; Bond and Cronkite; Bond and Robertson; Report of the United Nations Scientific Committee). Some dozen N-alkyl, N-aryl or N-acyl derivatives of cysteine have been reported to be protective, as well as other sulfur-containing compounds, e.g., thiourea. Certain compounds with branched or prolonged carbon chains such as 3-mereaptopropylguanidine are effective, as are a number of compounds with pronounced pharmacological and toxicological activity such as histamine, serotonin, DOPA, epinephrine, oxytocin, reserpine and apresoline, anesthetic agents, and ethyl aleohol. Other substances include sahieylie acid, zine, cobalt, magnesium, sulfate, chlorpromazine, chelating agents, morphine, linoleate, oxypolvgelatin, and certain vaccines. Reported protection by flavanones (Rekers and Field; Clark ef al.) was not found by others (Cronkite ef al. Buchanan ef al). To date no preprotective agent hax proved suitable for practical preprotection in the human being, and anv such agent of course would have to be given prior to exposure to be effective. cers Sigg, HE:AeeStan 220 i