That rickets is a disease that is readily prevented or cured by ultraviolet radiation from either artificial sources or sunshine is evident from the numerous investigations reported on this subject. Information as to the amount of radiation needed to cure rickets, with respect to the area exposed, is, however, very meager. Investigations made in conjunction with co-workers indicated that only a small amount of radiation is necessary for the cure or prevention of rickets in rats.1 When one considers that the rat is covered for the most part with fur, the amount of radiation that reaches the surface of the skin is no doubt much reduced. Maughan and Dye2 showed that in chickens only a small amount of radiation is necessary to cure rickets, and that the area covered by the feathers receives very little or perhaps none of the beneficial rays.
It seemed desirable, therefore, to determine