Further studies on the incidence of lymphomas in mice exposed to X-rays and given sex hormones.

been recognized for many years (1, 7, 11). Estro gen-treated mice of some strains have a higher incidence of lyrnphomas than untreated controls (5, 6), andtestosterone propionate decreased the incidence of such tumors when given with estro gen (5). Sex differences in the incidence of lym phomas in untreated mice have not been noted generally, but in mice of one strain, at least, fe males showed a higher incidence of lymphomas than did the males (13). As small an amount of testosterone propionate as S mg., administered as a pellet, lowered the incidence of lyinphomas in castrated female mice to approximately that of intact males. This experiment indicated that testosterone propionate reduced the incidence of lymphomas in mice of a susceptible strain. The incidence of lymphomas in irradiated mice was also decreased by the subsequent administra tion of testosterone propionate. Among roentgen irradiated female mice, the incidence of lym phomas was 20 per cent when testosterone was given subsequent to irradiation and 47 per cent in the placebo-treated irradiated controls (2). In tact testes reduce the incidence of mediastinal lymphomas as indicated by the present study. MATERIALS AND METHODS Three groups of 50 male and 50 female mice of the â€oeBC†• strain' were used. The groups were arranged so that litter S These investigations were supported in part by the Jane 1 â€oeBC†• refers to mice obtained by hybridizing mice oh tamed from Dr. H. B. Andervont (who in turn had obtained them from the colony of Drs. Pybus and Miller in England) with mice of the CSH strain. The hybrids were subsequently backerossed to the Pybus-Miller mice. These mice were selected for white coat color and were inbred brother-to-sister for up to 26 generations at this time. The controlmice used were from the ninth to the nineteenth generation of inbreeding, and the experimental animals from the eleventh to the fifteenth generations. These mice show responses to steroid hormones similar to those noted in the original Pybus-Miller mice. mates were placed in different groups. The female siblings were mentioned earlier in connection with ovarian tumors (2). At ages ranging from 31 to 92 days the mice were given total body irradiation of 285, 350, or 380 r.' Equal numbers from the three groups of male and three groups of female mice received comparable amounts of irradiation. Animals dying at ages of less than 150 days or that could …