THE EFFECT OF X-RAYS ON THE RICKETTSIOSTATIC ACTIVITY OF STREPTOMYCIN, AUREOMYCIN, AND PENICILLIN

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Abstract
Only a slight reversal of the rickettsiostatic action of 5 mg of streptomycin occurred in embryonate eggs given 100 r of X-rays at 4 days of incubation, whereas complete reversal occurred in those given 1000 r. Groups of eggs irradiated with intermediate doses of X-rays showed a graded response. The rickettsiostatic activity of 5 mg of penicillin or of 5 mg of Aureomycin was not reversed by 100 to 1000 r. 500 r reversed the rickettsiostatic activity of 2 mg, 4 mg, 8 mg, or 16 mg of streptomycin per egg in proportion to the amount of streptomycin injected. The rickettsiostatic activity of 2 mg of streptomycin was completely reversed and the activity of 16 mg only partially reversed. Reversal of the rickettsiostatic activity of streptomycin by X-rays was seen when radiation was given up to 6 days after the injection of the antibiotic into 7-day-old embryos. Reversal of the rickettsiostatic activity of 4 mg of streptomycin could be detected when the antibiotic was injected 4 days after 500 r of X-radiation.