Our subject matter being diathermy, by which is meant "heating through," it will not, perhaps, be amiss to discuss first the more generally known forms of heat so that we may better understand and appreciate the distinct differences of effect produced by these various modes of heating human tissue.
We speak of heat as being conductive, convective and conversive. Conduction is that form of heat which is conveyed to the body by virtue of direct contact with a superheated substance. It is the old-fashioned household method of applying heat whenever that therapy seemed to be indicated. As examples of this form we make mention of the hot water bottle, hot poultices, fomentations, electric pads and hot baths. These appliances transmit heat to the part with which they come in contact by fact of contiguity. Convective heat radiates from a source approximating, but not in contact with, the body. Thus the