The Relative Response of the Skin of Mice to X-radiation and Gamma Radiation

(1) Short lengths of the tails of mice were irradiated with X and γ radiation, so that the dose received was the same at all points throughout the irradiated portion of the tail for each radiation. (2) When thus irradiated with equal doses of X and γ radiation, measured in röntgens, the skin reactions were found to be markedly different. The ratio of effectiveness for erythema and desquamation was 1·3, and for epilation and exudation 1·6, the X radiation having the greater effect. (3) In all cases care was taken to keep the duration of irradiation so similar that variation in the time factor played no part in the results obtained. (4) Although the dose of radiation delivered throughout the whole of the irradiated portion of the tail was constant both for X and γ radiation, it does not follow that the amounts of energy released were identical. In the case of both qualities of X radiation used, elements of high atomic number, such as sulphur and calcium, give rise to strong photo-electric emission, which represents an additional contribution to the energy released in the immediate vicinity of these elements. (5) Consideration was given to the presence of sulphur in the skin and calcium in the bones of the tail (see following paper), and although it was not possible to account completely for the differences found, it seems that photo-electric absorption goes some way towards explaining the differences observed biologically. We should, therefore, hesitate to conclude from the present experiments that these differences were conditioned by wavelength, except in so far as wavelength may determine the energy released in the cell through the process of photo-electric absorption.