306 THE VITAMINS 



cholesterol or a contaminating substance had been activated. Soon after- 

 ward they reported that ergosterol, a substance having 3 double bonds 

 and an hydroxyl group, could be activated by irradiation. Since choles- 

 terol is usually contaminated by ergosterol they suggested that the latter 

 sterol is the substance which is activated into an antirachitic product by 

 irradiation with ultra-violet light. 



Windaus (1927) and Hess (1927) also reported simultaneously 

 upon this work in another form. 



Pohl (1927), working with the same materials as Windaus, showed 

 also that the absorption spectra of cholesterol and ergosterol were 

 similar. He found that after irradiation for 25 minutes the ergosterol 

 showed an absorption band only at about 240 ,m// instead of exhibiting 

 maxima at 293, 280 and 270 fxjx ; and attributed this band to vitamin D. 



Heilbron, Kamm and Morton (1927) found that cholesterol purified 

 by the usual methods contains another compound in small amount which 

 can be accumulated in a "least-soluble fraction." This substance was 

 found by them to show well-defined absorption bands at 293 ^ji, 280 mi 

 and 269 n(.i. "These bands disappear on irradiation with ultraviolet light 

 with concomitant appearance of antirachitic potency. It is obvious that 

 the unknown substance is closely related to the vitamin D precursor." 



Rosenheim and Webster (1927c) showed that cholesterol purified by 

 way of the dibromide cannot be activated by ultra-violet light, that it no 

 longer possesses the absorption spectrum in the ultra-violet region 

 which had formerly been considered characteristic for cholesterol (Hess 

 and Weinstock, 1925a; Schlutz and Morse, 1925), and that whereas 

 0.5 milligram irradiated cholesterol (as formerly prepared) would pre- 

 vent rickets in rats, doses up to 8 milligrams daily were impotent if the 

 cholesterol used were purified chemically. According to Rosenheim and 

 Webster, "The precursor of vitamin D is not cholesterol itself, but a 

 substance associated with cholesterol as obtained from all natural 

 sources. We have since extended these observations to the phytosterols, 

 and have found that when these are purified by way of the bromides, 

 they also yield no vitamin to irradiation ; whereas all vegetable oils and 

 the sterols obtained therefrom and not so purified, readily acquire anti- 

 rachitic properties under the action of ultraviolet rays." Ordinary 

 cholesterol may be freed from provitamin by purification through treat- 

 ment with bromine, or with thionyl chloride, by oxidation of the pro- 

 vitamin with potassium permanganate in acetone solution, by over- 

 irradiation and subsequent recrystallization, and by treatment with an 

 efficient charcoal. When cholesterol has been thus freed from pro- 

 vitamin, it shows only general absorption of ultra-violet light and cannot 



