Reflex sympathetic dystrophy or causalgia is a painful syndrome usually occurring after trauma to a limb, characterized by its own peculiar type of burning, diffuse pain, trigger points and manifestations of sympathetic stimulation such as, subjectively, a cold or hot limb and, objectively, rubor, pallor, or both, and swelling. There is often atrophy of the bone, characteristically mottled owing to spasm of the nutrient arteries, and sometimes atrophy of the skin and muscle. There may even be immobility of a joint, scleroderma and Dupuytren's contracture. An attractive theory of the mechanism of this pain is adopted from De Nó1 by Livingston2 in his monograph on "Pain Mechanisms." I have slightly modified this conception in figure 1. A prolonged bombardment of pain impulses sets up a vicious circle of reflexes spreading through a pool of many neuron connections upward, downward and even across the spinal cord, and perhaps reaching