"Sol est remediorum maximum." These are the words in which the elder Pliny ascribed a great remedial potency to the sun's rays. His dictum merely embodies, in the form of what would nowadays be termed a slogan, the long held belief in the value of the sun in curing and preventing disease. Generations of laymen as well as physicians have somehow assumed that part of the undoubted beneficial effects of an outdoor life is attributable to sunshine. The Greeks had their helioses and the Romans their solaria; yet heliotherapy has as yet scarcely emerged from the most empiric of performances into the dignity of a scientifically justified or rationalized procedure.
The pioneer experiences of Finsen with radiant therapy, and particularly the successes that Rollier and others have achieved by employing the direct rays of the sun in the treatment of certain types of local tuberculosis, naturally forced more serious attention
SUNLIGHT AND HELIOTHERAPY. JAMA. 1925;84(20):1498–1499. doi:10.1001/jama.1925.02660460034015