Abstract
The 30-day survival of F1 mice exposed to lethal irradiation (912 r) and injected with parent bone marrow is a function of the number of parent lymph node cells injected. This relationship was used as a calibration curve to determine the surviving proportion of a suspension of lymph node cells irradiated in vitro. The radiation response could be represented by a survival curve, the linear portion of which indicated a D37of 74 r and an extrapolation number of about2.7.