A thorough survey of the literature shows certain outstanding milestones in the progress toward the present knowledge of rickets. This has been so widely disseminated that it is necessary only to recall the names and contributions of the men concerned with it. Between the first work done by Glisson1 on etiology in 1650 and that of Mellanby2 in 1918 on an antirachitic factor or vitamin, there is a long lapse of time with little in the way of contributions to knowledge concerning the etiology of rickets. Following this, progress has been rapid and constructive. The demonstration by Huldschinsky3 in 1919 of the curative action of ultraviolet rays of the mercury vapor quartz lamp was followed by the observation of Hess and Unger4 in 1921 that sunshine had a similar action in infantile rickets. The following year, McCollum, Simmonds, Becker and Shipley5 submitted proof of the