Mice were inoculated by mouth at different times (2 hours, 5 days, and 11 days) after a single exposure to 550 r total body x-irradiation. The inocula contained approximately 107 Pseudomonas aeruginosa which was found to be quite harmless for unirradiated mice.

Comparison of the cumulative mortality curves and of the incidence of Pseudomonas bacteremia showed their susceptibility to infection by this route to be greatest on the 11th day, somewhat less on the 5th day post irradiation, and least of all directly after irradiation. Since damage to the intestinal mucosa has been found to be maximal within the first few hours after exposure to doses of x-irradiation in this range, it seems reasonable to conclude that the increased susceptibility is not due to increased permeability of the mucosa of the gut, but to impairment of the animal's natural defenses against infection.

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