The value of sunlight in the maintenance of health has been recognized from early ages, and history records sun-worship by many nations in the past as well as at the present time. In Europe records exist of the use of the light of the sun for medical and surgical purposes since before the Christian era, but it was only towards the end of the last century that its possibilities began to be studied and the value of the electric arc lamp as a substitute recognized. In 1893 Finsen demonstrated the value of sunlight and electric arc radiation in the treatment of lupus, and at the beginning of the present century Bernhard of Samaden treated wounds and tuberculous lesions with sunlight. In 1903 Rollier opened his first clinic at Leysin, where he obtained excellent results in the treatment of tuberculosis, especially of the surgical type, by insolation in the brilliant Alpine sunshine. In 1908 Gauvain introduced heliotherapy at Hayling Island and at Alton. Nagelschmidt used the air-cooled quartz mercury vapour lamp for general irradiation in the same year, and in 1913 Reyn commenced the use of the carbon arc for the same purpose. The value of ultra-violet rays in the cure of rickets was not recognized till demonstrated by Huldschinsky in 1918, though Palm (1), as early as 1890, urged that deficiency of sunshine was a cause of the condition.