624 X. VITAMINS D 



and Weinstock,^^"^^ in 1924-1925, that antirachitic activity could be im- 

 parted to certain foods by ultraviolet irradiation opened the avenue for the 

 synthesis and isolation of vitamin D. It was realized immediately that the 

 precursor of the active principle was in the category of a provitamin, and 

 that this was transformed into the physiologically -active form by the photo- 

 chemical effect of the ultraviolet rays. Shortly after the original findings, 

 various workers reported that the activated substance was originally a 

 sterol-like compound without antirachitic potency. ^""^^ Several groups 

 demonstrated almost simultaneously that provitamin D was ergosterol, or a 

 sterol with a structure similar to that of dehydrocholesterol.^^"*'' It was 

 discovered that there were several provitamins D, including not only ergos- 

 terol but also 22-dihydroergosterol,^* and 7-dehydrocholesterol. The physi- 

 isologic nature of the latter provitamin D was demonstrated when it was 

 isolated from hog skin.^^ It had previously been synthesized by Boer et 

 al}^ Moreover, a number of investigators^ ^~^^ showed that the vitamin D 

 in halibut and tvma oils consisted almost entirely of an ester identical with 

 the product obtained from activated 7-dehydrocholesterol. Crystalline 

 vitamin D2 (the form prepared from ergosterol) was isolated by Reerink and 

 van Wijk^^" in 1929, although Linsert^^ and Windaus, Linsert et al^^ are 



37 A. F. Hess, Am. J. Diseases Children, 28, 517-521 (1924). 



38 A. F. Hess and M. Weinstock, Proc. Soc. Exptl. Biol. Med., 22, 5-6, 6-7 (1924- 

 1925). 



39 A. F. Hess and M. Weinstock, /. Biol. Chem., 62, 301-313 (1924). 



« A. F. Hess, M. Weinstock, and F. D. Helman, J. Biol. Chem., 63, 305-308 (1925). 



« H. Steenbock and A. Black, J. Biol. Chem., 64, 263-298 (1925). 



« O. Rosenheim and T. A. Webster, Lancet, 1925, 1, 1025-1026. 



"R. Pohl, Nachr. Ges. Wiss. Gottingen, Math-physik. Klasse, III, 185-191 (1926). 



" A. Windaus and A. F. Hess, Nachr. Ges. Wiss. Gottingen, Math-physik. Klasse, III, 

 175-184 (1926). 



■'s A. Windaus and F. Holtz, Nachr. Ges. Wiss. Gottingen, Math-physik. Klasse, III, 

 217-225 (1927). 



« O. Rosenheim and T. A. Webster, Lancet, 1927, I, 306-307. 



«0. Rosenheim and T. A. Webster, Biochem. J., 21, 389-397 (1927). 



« A. Windaus and R. Langer, Ann., 508, 105-114 (1933). 



« A. Windaus and F. Bock, Z. ph^jsiol. Chem., 2^5, 168-170 (1937). 



^^ A. G. Boer, E. H. Reerink, A. van Wijk, and J. van Niekerk, Proc. Acad. Sci. 

 Amsterdam, 39, 622-632 (1936). 



61 H. Brockmann, Z. phijsiol. Chem., 241, 104-115 (1936). 



62 H. Brockmann, Z. physiol. Chem., 245, 96-102 (1937). 



" H. Brockmann and A. Basse, Z. physiol. Chem., 249, 176-180 (1937). 

 " E. J. H. Simons and T. F. Zucker, J. Am. Chem. Soc, 58, 2655 (1936). 

 66 G. A. D. Haslewood and J. C. Drummond, Chemistry & Industry, I4 (J- Soc. Chem,. 

 Ind., 55) 598-599 (1936). 



66 E. H. Reerink and A. van Wijk, Biochem. J., 23, 1294-1307 (1929). 



67 E. H. Reerink and A. van Wijk, Biochem. J., 25, 1001-1010 (1931). 



68 O. Linsert, annotation in Ann., 489, 269 (1931). 



69 A. Windaus, O. Linsert, A. Luttringhaus, and G. Weidlich, Ann., 492, 226-241 

 (1931). . 



