It is well known that commercial cholesterol, when irradiated with ultraviolet light, can be used to cure patients with rickets. In 1925, Windhaus,1 Hess, and Rosenheim and Webster2 showed that when commercial cholesterol is further purified by using animal charcoal, by oxidation, by distilling in a high vacuum or by using dibromides and then is irradiated, it is not effective in curing animals with rickets. Such attempts at separating pure cholesterol also change the absorption spectrum of the cholesterol. Windhaus, who had worked with sterols for many years, noted that ergosterol resembles cholesterol in its physical and chemical properties, but possesses three unsaturated carbon atoms. Ergosterol could easily be taken up, therefore, by oxidation, halogens, and the like; so Windhaus suspected that ergosterol is the substance responsible for the antirachitic value of irradiated commercial cholesterol.
Windhaus3 next mixed ergosterol with purified cholesterol and obtained the typical absorption