Introduction
Many factors contribute to the production of congenital malformations. It is the job of the experimentalist to decide what is their relative importance and to uncover all the contributing factors and their interrelationships.This same philosophy applies to congenital malformations caused by one etiology, namely, irradiation. The factors responsible for radiation teratogenesis are multiple and interrelated. Any classification would be completely arbitrary. For the purposes of this paper, the role of radiation can be thought of as mediated directly through the embryo, and indirectly through irradiation of the placenta and/or mother. It is the purpose of this and the subsequent paper to decide on how important these so-called indirect effects are in radiation teratogenesis, and not to determine the nature of these effects.Previous to the work of Wilson, Karr, Jordan, and Brent, all pregnant mammals were given whole-body irradiation, and therefore the direct and indirect factors could not