The action of X-rays on Colpidium Colpoda

Abstract

The action of X-rays on living tissues is a subject not only of much practical importance, but also of considerable theoretical interest. While there is in existence an immense accumulation of observations on the subject of the most varied kind, comparatively little of it has that numerical basis which is necessary for the foundation of any physical theory of the action. Some little time ago I ventured to suggest that some interesting results obtained by Strangeways and Oakley on the action of X-rays on tissue cells could be accounted for by the well-known discontinuous nature of the absorption of X-rays by matter, assuming that the structures in the cell which were vitally affected by the rays were sufficiently small for this effect to come into operation. Calculation showed that the size of structure required was not unduly small in comparison with that of structures known to exist in tissue cells. These results were explained on the assumption that a single ionisation by the X-rays of the particle concerned would be sufficient to produce the observed biological change. An extension of the theory to cover cases in which a succession of such hits is required presents no great difficulty, and the relationships obtained in this way between survival and dosage are found to agree, generally, with the results of other experiments, as, for example, those of Dr. F. C. Wood on cancer cells. I had been hoping that results would be published which would enable the theory to be tested numerically, but, so far as I am aware, such numerical results have not appeared. The present experiments were commenced in the hope of obtaining such numerical data.