In 1919, Huldschinsky1 pointed out the value of ultraviolet rays in the healing of rickets. Somewhat later, Hess and Unger2 and others reported that sunlight possessed the same beneficial action on rickets that ultraviolet light had. According to McCollum,3 cod liver oil has been used for at least one hundred years for conditions that were probably of a rachitic nature. The ability of medical agencies as well as of hygienic ones to affect favorably the outcome of a rachitic process moved Park, Powers and Guy4 to remark that "the similarity between the action of cod liver oil and that of radiant energy in rickets is so close that a connection must exist between them."
In 1924, Hess5 and Steenbock and Nelson,6 working indepently, were able to demonstrate that various foods known to be inadequate in the cure of rickets could be made therapeutically potent