The production of antirachitic substances of remarkable potency by suitable irradiation of inactive components of animals and plants represents one of the notable biochemical contributions of recent years to medicine.1 The most important, if not actually the only, substance that assumes antirachitic potency on exposure to ultraviolet rays is ergosterol, a formerly little known sterol, a crystallizable compound that can be secured in abundance in a state of great purity. The irradiated derivative of ergosterol, viosterol, which is assumed to be comparable if not actually identical in action with vitamin D, may exhibit a physiologic potency many thousand times that of cod liver oil, the foremost antirachitic product that occurs naturally.
It has been apparent for some time that the irradiation products of ergosterol represent a mixture of substances of which only a varying proportion is the active vitamin D. Consequently the question has arisen whether the toxicity known
CRYSTALLINE VITAMIN D. JAMA. 1933;100(6):426. doi:10.1001/jama.1933.02740060042014