GENESIS OF VITAMIN D IN THE BODY BY ULTRAVIOLET IRRADIATION

There is no longer any question about the potency of ultraviolet irradiation as well as sunlight in affording protection against or cure of rickets. The presumption is that somewhere and somehow the selective rays develop vitamin D or its equivalent, just as the antirachitic vitamin is formed by suitable irradiation of foods and most specifically of the organic substance ergosterol. There are at least two possibilities for the formation of vitamin D through direct irradiation of the surface of the body. The sebaceous material of the skin doubtless contains a substance susceptible to effective irradiation; at any rate "lanolin," the sebaceous lubricant of the skin and wool of sheep, can be rendered antirachitic by exposure to ultraviolet rays, as Hess, Weinstock and Helman¹ observed in 1925. There is evidence, too, that irradiated ergosterol-bearing sterol mixtures, if gently rubbed into the intact shaven skin, can protect rabbits on a rachitogenic