Measurement and Control of Some Direct and Indirect Effects of X-Radiation.

URING the first two decades following MULLER'S (1927) proof that D irradiation induced genetic changes, most of the effect was considered to result from ionizations (and excitations) within the chromosome itself. LEA (1946) interpreted the evidences accumulated up to that time as indicating that most genetic damage was induced directly, although he believed that ionizing and ultraviolet radiations produced also indirect effects on other components of the cells, which contributed a small part of the total effect. Such a view is no longer tenable. THODAY and READ (1947) showed that the frequency of chromosomal abnormalities induced by X-rays in Viciu fuba was several times as great in air as it was in nitrogen for the same dosage. KOTVAL and GRAY (1947) concluded that about one-half of the effect of alpha radiation in breaking prophase chromosomes of Tradescantia must be due to energy absorbed in the medium surrounding the chromosome.. That same year STONE, WYSS and HAAS (1947) demonstrated that the irradiation of the substrate with ultraviolet light, prior to growing bacteria in the irradiated medium, increased the mutation rate in these microorganisms. WYSS, STONE and CLARK (1947) showed that a similar increase in mutation rates in microorganisms could be accomplished by adding H202 (one of the active radicals produced in water by ultraviolet, or by X-rays if oxygen is present) to the substrate prior to inoculation. These investigations provided both inferential and direct evidence that radiation-induced chemical changes occurring outside the chromosomes ma)subsequently induce genetic changes. The discovery of these radiation-induced chemical mutagens may permit a comparison of the effect of radiation with chemical mutagens, such as those described by AUERBACH and ROBSON (1946). The present study is an investigation of the effect of changing the environment of mature sperm during irradiation on the production of chromosome rearrangements. The results were reported briefly ( HAAS, DUDGEON, CLAYTON and STONE 1952).