In the field of Roentgen ray therapy we are still a band of pioneers endeavoring to discover the possibilities of this new and mysterious agent. Its first decade has been productive of much new and valuable knowledge concerning the therapy of those diseased conditions which have heretofore proven most obstinate to all forms of treatment. We should be slow to condemn the ray because it has not fulfilled the expectations of the early enthusiasts, or because the results and observations of different operators have varied so greatly. It is only natural that the results should differ when we consider how great are the variations in the agent itself and the methods of application. What it has undoubtedly accomplished should be our standard and the beacon light to guide us in establishing its real value. To determine the value of the ray as a therapeutic agent we have to consider, first,