Wasted radiation is accounted for by the transformation of a latent form into an actual form of injury at a given measurable rate. The numerical parame- ters entering the equation may be computed from experimental results in cases of chronic and acute irradiation. Weekly exposure to gamma-radiation of burros, between 175 and 2800 R, with corresponding mean survival times of 9 to 1 week, were the time-dose conditions in which the above formula was found to apply. They are clearly of little value to the present discussion referring to low-dose-rates and to extended survival times. in a review of data on recovery Storer [S8, S9] rates and their possible relationships to life-shortening showed that the mean rate at which mice recovered from radiation exposures, which if acute would result in acute death, could be related to the number of fractions delivered daily, rather than to the size of the exposure. This and other observations suggested modifications of the origi- nal formulation of Blair. 2h, Krebs, Brauer and Kalbach [K3] measured the kinetics of non-recoverable injury by exposing C3H female mice to conditioning irradiations (600 to 1500 R) and then estimating at different times (4 to 20 weeks) the injury remaining. This estimate was obtained indirectly by taking the LD irradiated mice. A proportionality values on the pre- between conditions dose and reduction in tolerance to x rays, as measured by a reduction of LDS 9/30? was found; however, the injury parameter did not account for the observed mortality when animals were irradiated chronically. Further work [K4, K5] suggested in fact that different recovery components with different half-—times could be shown to apply to acute and chronic radiation exposure conditions. 25. Complete disappearance of residual damage was seen by Alexander and Connell [A4] three weeks after conditioning exposures of 600 to 1100 R prior to LD determinations. Spalding et al. [S10] gave conditioning frac- tionarcasoses of gamma rays (240 to 1200 rad) or of fission neutrons (92 to 451 rad) to RF female mice and, after a repair period of 3 months, exposed them for the rest of their life to a dose rate of 50 rad/day. They found that radiation-induced damage had a permanent and irreversible component, that at least a part of this damage was proportional to the dose and measurable in terms of reduction of survival time, and that fission neutrons pro- duced about five times as much irreversible injury than gamma rays. Always with the same animals, an investigation of the two-component theory of Blair