The effect of maternal rachitogenic diets on the skeleton of the fetus in rats has been studied by various methods. Toverud1 stated that female rats fed a low calcium diet did not breed sufficient offspring to permit study of the effect of the diet. Korenchevsky and Carr2 found the chemical composition of the young of mothers fed a diet deficient in fat-soluble factors identical with that of the offspring of control animals. These authors expressed the opinion that the normal chemical composition of the fetuses born of mothers fed the deficient diet could be accounted for by "the fact" that the maternal organism will so far as possible yield all the necessary substances to the offspring by the sacrifice of its own tissue. These early experiments illustrate the chief difficulty encountered in attempts to produce prenatal deficiency diseases in the young by feeding a deficient diet to the