The value of heat as a potent agent in treating disease has long been recognized. Therapeutic heat is given in various ways; its penetration formerly depended on radiation from some hot, external object. With the advent of diathermy1 a new form of application of heat was given to the medical profession. The value of diathermy theorectically depends on the development of heat within the tissues by the passage of a high frequency electric current through them. Whether there is some as yet unknown electromagnetic effect remains for further study, and does not fall within the scope of this paper. Because the heat is generated within the tissues, instead of coming from an external object, it should be more penetrating and, therefore, more effective than any other previous thermotherapy. Such claims are advanced in the literature, although since the time of d'Arsonval insufficient scientific investigation has been made to prove