The Action of Ionizing Radiations on Biological Materials: Facts and Theories

Abstract

In this paper1 I shall endeavor to give a fairly wide survey of the state of radiobiology from my own point of view. I am quite aware that my approach as a physical chemist is very incomplete. It will be necessary for me to pick and choose, and I am afraid that I shall have to ignore many interesting and important phenomena. It seems to me that the present stage of radiobiology is one in which there are few new concepts; there is in progress a gathering of information on structure in biological systems which is still far from complete, but which is necessary before new advances can be expected. The basic puzzle of radiobiology which has been stressed by L. H. Gray (1), is still unsolved, i.e., the fact that comparatively small doses of radiation produce marked biological changes and, in the case of animals, death, although in general rather large doses of radiation are required to produce easily observable chemical changes. The passage of radiation through living tissues obviously initiates a long chain of events. We have (1) the primary ionizations, (2) the chemical consequences, (3) the biological events which follow. Although the physical nature of the primary actions has been well worked out, and the chemical consequences have been established at least in numerous simple cases, the link between the chemical changes and the biological consequences is almost completely unknown. The reason for this no doubt has been our ignorance of the structure and organization of the cell. It is true that we have much detailed biochemical information about the working of the various biochemical systems, but how their actions are coordinated with each other is largely unknown. It must also be borne in mind that the cell is not a static system; it is a dynamic process, and the effects of the passage of an ionizing particle are determined not only by its immediate action in one place but by its effect on the sequence of events. I should like to point out at the start that a lethal dose of ionizing radiations produces a not insignificant number of chemical events, although it is still small com-