Abstract
It has been recently shown by Russell (1), Wilson et al. (2-4) and Hicks (5) that the sensitivity of the mouse and rat embryo to X-irradiation changes throughout gestation, with respect to both lethality and the production of malformations. The work of Wilson and his collaborators, on the rat, showed that when irradiation was administered after 9 or 10 days of gestation, 100 r would greatly increase the percentage of dead and resorbed embryos as well as produce abnormalities characteristic of the day, the ninth day having a greater effect in this respect as well as producing a greater depression of weight. On the eighth day of gestation, however, doses up to and including 100 r did not increase mortality above control levels nor produce any malformations, although weight depression was greater than on either of the other 2 days. Irradiation at this time with 200 r killed almost all the embryos within 3 days. This was a greater lethal effect than that produced by the same exposure on the subsequent days. Hicks found similar results at these times and extended the work to later stages. Russell had previously found that irradiation at comparable times during the gestation of the mouse produced the same effect in a qualitative sense, but that slightly higher doses were required. Warren and Dixon (6, 7) had earlier studied the effects of continuous radiation of the chick embryo at various times during gestation by injecting radioactive phosphorus (p32) into the yolk. The effects of this irradiation were not so striking as those of X-irradiation on rodents; there was a great reduction in size, but very few deaths and no malformations were produced. There are many possible explanations
Published Version
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