Role of Externally Produced Hydrogen Peroxide in Damage to Paramecium aurelia by X Rays. ∗

Abstract

Summary

The production of nongenetic death and division delay by X-rays is greatly enhanced if the paramecia are irradiated in a dilute medium with very few bacteria rather than the usual lettuce infusion with many bacteria. This effect is shown to be accounted for almost entirely by relatively stable substances produced by irradiation of this medium. About two-thirds of the total effect can be attributed to H₂O₂ or its reaction products, while the rest results from an action on the medium not due to H₂O₂. On the other hand, the frequency of genetic changes is not affected by the medium in which the organisms are irradiated nor does irradiated medium or medium to which H₂O₂ was added induce such changes. The failure to find an effect upon the genetic mechanism is interpreted as probably the result of the failure of the substances produced in the medium to reach the micronuclei which are situated some microns below the cell surface. The corollary to this is that the nongenetic changes are due to alterations in the superficial layers of the cell.