effectiveness and efficiency of the dose, It is the dose rate influence on these efficient doses that is important in considering the possible influence of dose and dose rate reduction to levels of interest in radiation protection. The author neglects this distinction in his selection of reports for presentation in this paragraph. While the material Sanders (11) administered to rats was derived from crushed ?38Pu0, microspheres, the animals did not receive crushe 4 238 PuO» microspheres. The material had been stored in a saline solution for a long period of time and had been altered to a non-crystalline form of plutonium (i.e., it had no detectable x-ray diffraction pattern) throught to be solubilized in the saline and "monomeric" 238pu in form. Page 5, line 25 to Page 6, line 20 - "Based on the above considerations it is evident that the tumor risk is optimized when a very large number of cells and their descendants are subjected to only a few widely spaced alpha interactions with the small target afforded by the cell chromosomes, This follows necessarily from the fact that most alpha interactions with cell chromosomes lead to the subsequent mitotic death of the cell, as Barendsen has shown(17;18)_, The production of a malignant cell calls for a sequence of two or more low probability events and thus cannot be speeded up by the application of massive alpha doses, but rather only by subjecting a much larger number of cells to a limited number of interactions. Additionally, assuming that the tumor risk to the tissue subjected to alpha irradiation is proportional to R22 (t/T.); explained above, it is apparent that the alpha activity concentration or the activity per particle which is equated to a given tumor risk decreases with increasing time of exposure and also that a given risk can be attributed to smaller cumulative doses when the time of exposure (573is appreciabty, longer than the mean life of the cell, T,. Brues¢ and Burch(2 (33°3 pointed out that the two-mutation theories of carcinogenesis 20,21) would imply an exceptionally high effectiveness of widely spaced radiation for tumor production. It is proposed that just such a dose rate relationship serves to reconcile the observed significant tumor risk in cigarette smokers with the presence of a persistent lung burden of insoluble smoke particles involving a total of only a few picocuries of 210pg(14) on