Abstract
In a recent number of this Journal there appeared a paper by Packard (1), dealing with the quantitative effect of X-rays on Drosophila eggs. The mortality curves obtained were of sigmoid form, and conclusion was drawn that the shape of the curve is an expression of the varying susceptibility of the eggs to the rays. A similar piece of work has been recently carried out by Crowther (2) using X-rays and the Infusorian, Colpidium colpoda. Sigmoid mortality curves were likewise obtained, but in contrast to Packard, Crowther interprets these as being due to variation on the side of the radiation, and thus as probability curves. This interpretation necessarily requires the vulnerable part of the organism to be very small, as each organism as a whole receives within a very small percentage the same dose of radiation. Dealing with the problem mathematically Crowther calculates that the size of the vulnerable part is 3.5 × 10–5 cm., and that it must be hit 49 times to produce immediate death, and 42 times to cause death within an hour. Although a solution of this kind may be obtained on the hypothesis that the variation is on the side of the radiation, it does not follow that this represents in any way the mode of action of the radiation. It is important, therefore, to decide which of these interpretations is the correct one, and for the purpose I submit the following experimental results. The organism used was Colpidium colpoda. This has been submitted to β-radiation from radium emanation and from radium, to ultra-violet radiation, and to phenol. In all cases sigmoid curves were obtained similar to these of Packard and Crowther, and in view of the similarity of the results obtained details of the experiments are not given.
Published Version
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