Results For norm. aal CBA/H mice given the x-irradiation in 14 minutes the LDss is 950 rad. $ The LDss is 1,340 rad when the dose is spread over 25 hours. CBA/H mice injected intravenously one week previously with 10'leukaemic cells, and then acutely irradiated with a dose of 950 rad and treated with isologous bone marrow or infant spleen, died after about a month with generalized leukaemia.(Mean survival of a group of 10 treated mice was 31.6 days (SD 8.0 days) from the time of irradiation, compared with 8.5 days (SD 2.6 days) of 10 unirradiated control mice.)

On the other hand, CBA/H mice injected one weekpreviously with 10'leukaemic cells, irradiated over 25 hours to a doseof 1,500 rad, and then treated with bone marrow or infant spleen have shown survival of three months and longer in three successive experiments (see Table).