Adequate and successful use of physical agents can be expected only if there is understanding of the basic physiologic concepts underlying their use and application. It would be impossible to discuss here the basis for all of the modes of treatment employed in physical medicine. Therefore, this paper is being limited and is designed primarily to present some of the information that has been and is being accumulated in experimental work.
The agent most commonly employed in physical medicine is heat. Despite wide application of heat in the treatment of many conditions, its physiologic effects are poorly understood. Two factors must always be considered in heat therapy: (a) the amount of heat successfully applied to the tissues, i. e., the resultant of heat input and heat loss, and (b) the extra amount of heat produced in the tissues as a consequence of oxidative processes which have been accelerated by the