Denuded nerve fibers containing the node of Ranvier were prepared from the nerve innervating the gastrocnemius muscle of the frog. The effects of temperature rise of the medium surrounding the naked nerve fibers were studied upon the muscle response. A rise in temperature of the order of 50˚ ~ 90℃ was proved ineffective in the production of contractions in the muscle. It is thus concluded that the widespread concept that heating is one of the nerve stimuli is inadequate, and that thermal pain is the indirect effect of thermal stimuli. The authors standpoint about thermal stimulus is that thermal stimulus or heating is one thing, cooling is another.