Effects of fractionated doses of x-radiation on normal and tumor tissue.

Our investigations (5,6) concerned with quanti tative data on problems of growth, regeneration, and the differential response of normal tissue to changes induced by x-radiation in the testes of mice are now augmented by further data on testes, on germinal cells in the ovary, and on mouse tumors. These studies confirm the belief that there is more than one kind of resting spermatogonia and that they differ in their resistance to x-radiation. The investigation also reveals that some germinal cells in the ovary have relatively the same order of radio-resistance as the corresponding cells in the testis. Some cells of the transplantable and spon taneous tumors are more resistant than the sper matogonia or oocytes in the gonads of the same species. Under the conditions of our experiment, it appears doubtful that fractionated doses of xradiation produce resistance. A review of the literature regarding the general effect of irradiation on the testis is included in a previous publication (5). The differential response of the germinal ele ments in the testes of adult pure strain mice sub jected to acute direct x-radiation follows a charac teristic pattern as demonstrated by the quantita tive random sampling method previously de scribed (5, 6). It was shown that by plotting fre quency of appearance of any of the germinal ele ments against time, for any of the doses used there was (a) a period of decrease, (o) a period where there were no alterations in the number of spermatogonia, and (c) recovery for the lower dose range. One purpose of this investigation was to ascertain what effect repeated doses would have on the spermatogonia of the testes when given at