- 28 continuous irradiation increases the incidence of mutated cells capable ‘of reproduction, but only up to the point at which the continuing irradiation and increasing dose begins to sterilize oekil more of such reproductively capable mutated cells than it is producing. Compared with x- or Y~rays, alpha particles are highly efficient for killing or reproductively sterilizing cells, so that ror equivaient dose parameters, the fraction of cells surviving and capable of reproducing themselves as well as carrying chromosomal aberrations and mutations, is very small for alpha radiation. But the amount of tissue damage and disorganization, which requires larger doses for production than does chromosomal aberration or mutation, and which may also be an important factor in mechanisms of carcinogenesis, is relatively greater for the high LET alpha radiation. . Page 13, lines 22-23 - "Therefore the tumor incidence per alpha disintegration must increase with decreasing dose rate." Comments: This sentence seems enigmatic, non-sequitus and perhaps incompatible with the author's previous sentence. Perhaps it depends upon what the author means by his newly injected dose parameter, “per alpha disintegra- tion,” as compared with his meaning of "dose" (rad?) and of "decreasing dose rate." If he intends to mean by "gecreasing dose rate" the decreasing dose rate in an organ with increasing time after a given alpha emitter burden to that organ, and then intends to relate this lowered dose rate with the delayed appearance of cancer after a long latent period, it should be pointed out that the earlier high dose ‘rate may be the rate more associated witn the cancer induction. On the other hand, if he intends to mean a comparison of different dose rates,