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A brief study of the effect of X-ray treatment in vitro upon the culturability, reproduction and infectivity of Endamoeba histolytica was carried out. It was observed that single irradiations up to 120,000 roentgen units failed to kill or inactivate the organisms in Shaffer-Frye and Balamuth media. Exposure of the “streptobacillus” up to 120,000 r failed to produce any change in its ability to permit growth of amebae in S-F medium. Exposure of amebae in Balamuth culture up to 30,000 r did not seem to affect visibly the normal cycle of population growth. On the other hand, exposures to 60,000 and 120,000 r seemed to inhibit somewhat amebic population growth. Whether this was due to the fact that these doses were lethal for most of the amebae or whether they just prevented or slowed down reproduction is impossible to state on the basis of the evidence presented here. It is unlikely, however, that inhibition of growth was due to the action of X-ray on the accompanying bacterial flora, in view of the fact that amebic growth in the tubes that had been preconditioned with unexposed bacteria was also inhibited. No difference in population growth was observed in the groups that had been treated with neutral red and their controls. Viable amebae were observed for 16 transfers after irradiation with 120,000 roentgens. Injection of the progeny of the X-rayed amebae (120,000 r) into normal guinea pigs produced severe intestinal lesions like their unexposed controls.
All of the Department of Tropical Medicine and Public Health, Tulane University, New Orleans, La.