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October 9, 1967

Lethal Radiation in Animals

JAMA. 1967;202(2):152. doi:10.1001/jama.1967.03130150120032

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To the Editor:—  The editorial on accidental radiation injury in man describes three lethal dose-dependent clinical states, the mildest of which, hematopoietic failure, is considered reversible if given good care (200:885, 1967). Since certain parallels exist between man and rat in their responses to radiation exposure, we would like to call attention to some relevant experimental data.The mortality of rats exposed to whole-body radiation in the midlethal range ( 550 rads), which is nearly 100%, can be reduced to near zero if the intestinal coliform flora is suppressed by an orally administered nonabsorbable antibiotic (J Exp Med48:935, 1967). The protection is maximal if it is started shortly before radiation or immediately afterward. For full recovery from the injury, the antibiotic is needed up to 21 days after exposure. This protection is lost if bacterial endotoxin is fed to such animals. Therefore, the conclusion is warranted that bacteria