THE last few years have brought us important developments of measuring apparatus and measuring methods, the intelligent application of which enables the roentgenologist to reproduce a certain dose in X-ray therapy. Physical (e-unit, roentgen unit) and biological (erythema dose, skin unit dose) units have been introduced and are generally accepted, to express the amount of roentgen energy applied to the human skin. Very little use has been made of these factors in the diagnostic branch of roentgenology, although there is no doubt regarding the necessity of establishing some definite idea of the tolerance dose of roentgen energy as delivered by the diagnostic apparatus and tubes in operation to-day. The fact that there are cases reaching the courts every year claiming damage for an alleged overdose received in connection with a roentgen-ray examination warrants this investigation. It is well known that the majority of such patients have been subjected to a fluoroscopic examination, either for the removal of...