That the X-rays may seriously alter the action of living cells, even to such an extent as to induce a stubborn and intractable form of carcinoma, has long been recognized. The hundred and forty or more victims among the radiographers of the world bear mute and incontrovertible testimony to this fact. There is, however, another phase, more subtle and menacing, to the deleterious action of irradiation, which has been attracting the attention of radiographers and physicians generally in recent years. This is the obscure action of the rays in arresting normal embryonic growth or in inducing a perverted cell-growth which will result in the production of congenital physical or mental defects of varying grades of severity following irradiation of the pregnant woman. That such a possibility existed has been strenuously denied by many workers in the rays. It is only after the publication of what appear to be authentic reports of such deplorable results by trustworthy authorities of this and other countries that it has become obligatory to concede the possibility. To Bailey and Bagg, of the United States, and Schmitt, of Germany, must be given the credit of emphasizing the danger, even in the face of active opposition by incredulous observers. These men have collated all the reports of cases of congenital injury after irradiation during pregnancy. These vary from embryonic death with abortion to monstrous development and different grades of post-natal retardation of physical growth, with or without mental deterioration. While these cases have been numerous enough to merit recognition, the relative proportion of developmental retardation to normal growth of the off spring is very small, although not negligible. There is certainly no reason for an hysterical outcry against the use of the rays in pregnancy whenever they are urgently indicated. It becomes, under these circumstances, the choice of the lesser of two evils—whether the existing dangerous condition shall be allowed to continue untreated, or the off spring be subjected to the remote possibility of permanent injury to its developing cells, a problematic accident at the best. It seems to us that a distinction must be drawn between the dosages of the rays as required for diagnostic and therapeutic purposes. The comparatively trifling exposure of a few seconds that is required for the making of a diagnostic plate will probably be attended by no serious consequences. The thousands of pregnant women who have been irradiated at various stages of gestation for this purpose without untoward consequences to themselves or their offspring provide ample proof of the apparent harmlessness of the process. Even here, however, it is too early as yet to determine whether a remote developmental retardation will be manifested in these children. Time alone, with careful, painstaking, scientific investigation of the children, with proper check observations, can settle this question.