Radium and Lethal Mutations in Drosophila Further Evidence of the Proportionality Rule from a Study of the Effects of Equivalent Doses Differently Applied

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Abstract
Exps, planned with a view to determining within what limits the proportionality rule holds show again a strict correspondence between the amt. of radium administered and the consequent biological effect, the induced mutation frequency obtained varying directly with the dosage. A series of dosages as nearly exactly equivalent as possible but applied in different ways gave approx. equivalent results, dependence being merely upon the total energy absorbed. Whether the treatment consists of a high intensity and a short exposure or low intensity and long exposure, the dosage expressed in r-units is remarkably constant. Within the limits set for the present investigation (2 mgm. radium for 150 hrs. to 300 mgm. radium for 1 hr.), a small amt. of radiation does not seem to have a disproportionately great effect owing to its being applied over a long period. Perhaps dispro-portionality begins outside even these wide limits, and, if so, there is still a possibility that a small amt. of natural radiation acting a very long time might be sufficiently effective to account for natural mutations.