Shortly after the discovery of the production of vitamin D by the irradiation of ergosterol, the observation was made that the antirachitic effect on chickens of the irradiated ergosterol differed markedly from that of cod liver oil, rat unit for rat unit of vitamin D.1 This raised the question of the relative efficacy in human beings of the various
vitamin D-containing substances and the dosage of each necessary for the prevention and cure of infantile rickets. For some years it has been customary to administer daily for the prevention of rickets 3 teaspoonfuls of cod liver oil, which amount contains approximately 1,000 U. S. P. units of vitamin D, or 10 drops of standard viosterol (10,000 U. S. P. [international] units of vitamin D per gram), which dose contains approximately 2,000 units. In table 1 are given most of the commonly used vitamin D products, with the number of