Direct application of heat is one of the prime resources of first-aid. A canteen will do instead of a hot-water bag, or a hot stone may be rolled in blanketing or other thick cloth; but a better expedient, because it shapes itself to whatever part it is applied to, is a bag partly filled with hot sand, salt, rice, or the like. The stuff may be heated quickly in a frying-pan. If the patient is unconscious, you must be careful not to burn him. Observe his skin, frequently, and feel the cover of the hot article, which should not rise above 115 deg.

To produce the most effect, heat should be applied between the thighs, between the arms and the body, and to the soles of the feet. Cloths wrung out in hot water, then inclosed in dry ones, are the best means to reduce swelling after an injury.

Cold is used also to reduce swelling, as well as to stimulate breathing, and to reduce temperature in sunstroke. Of course, ice cannot be obtained in the wilderness, save in winter, but, if the affected part cannot be soaked in a running stream, then cloths may be wrung out in water from a spring or cold brook, or an arrangement can be rigged to discharge a continuous stream of it upon the patient.