Definite knowledge regarding rickets in the human and other mammals has developed rapidly during the past few years, due to the discovery of some of the important factors in the causation of the disease. The influence of supply and balance of calcium and phosphorus in the diet has been studied quite carefully. Certain substances, such as cod liver oil and egg yolk, have been shown definitely to contain something (anti-rachitic vitamin) which is capable of preventing and curing rickets. Quite a complete review of the literature on experimental rickets may be found in Korenchevsky’s1 publication.The demonstration by Huldschinsky,23 then by Hess, Unger, and Pappenheimer4, that ultraviolet rays play an important part in the prevention and cure of rickets, answered some of the perplexing questions which had arisen regarding the cause of the disease. Before this fact was discovered it was extremely difficult to account for the .