Dr. Levick first deduced that neurasthenia in grown-ups and rickets in the young are due to the same cause. Both these diseases, he claims, are nutritional disturbances of the nerve centers affecting the bones in the young, and the nervous systems in the old. The action of sunlight on the skin forms a substance which is carried into the blood and feeds the nerve centers as well as the bones. His success in treating neurasthenia with sun’s rays led him to apply it to cases of infantile paralysis, a disease which is a severe shock to the nervous system and which results in muscular atrophy. Under the action of sunlight a renutrition of nerve centers takes place. Synthetic sunlight produced by him with an electric arc light of his own invention proved as good as natural sunlight, and could be better regulated to the patient’s endurance. He used two distinct kinds of light-rays, the short ultra-violet rays for nerve nutrition, and the long red and infra-red rays for muscle treatment. Red rays, as can be seen when the hand is held up against the sunlight, penetrate the flesh to a considerable extent, and can therefore stimulate the sleeping muscle. Dr. Levick warns that immediate success must not be expected. He has found constant improvement where short daily treatments were continued over a period of several years. While the method may not be effective in extreme cases, it is nevertheless a test which will soon show after a few treatments whether any rejuvenation of the nerve fiber is taking place. It is now admitted that the (red) heat-waves may play some part in heliotherapy—exposure to direct sunlight for medical purposes. Dr. Lazarus-Barlow, Professor of Experimental Pathology in the University of London, concludes that even though heat-rays may also play some part in curative processes, “experience of the treatment of wounds by sunlight in France during the World War indicated that a degree of benefit arises from exposure to sunlight which cannot be attributable to warmth and ultra-violet rays. On the other hand, in the Finsen light treatment of lupus (a tubercular affection of the skin of the face, occurring in several forms) and in the treatment of tuberculosis at high altitudes, ultra-violet rays play a predominant part.” As the ultra-violet rays penetrate but a fraction of a millimeter into the epithelium, “it is uncertain how the rays act.” The suggestion is here ventured that since the recently discovered Millikan Rays are particularly powerful under the same conditions that make application of the ultra-violet rays practicable as a therapeutic agency, it may later be found that these highly penetrating rays, of exceedingly short wave length, aid greatly in effecting some of the cures now attributed wholly to the longer (and less penetrating) ultra-violet rays or the much shorter X-rays.[7]