INTRODUCTION 635 



ergosterol in the gastrointestinal tract, in contradistijiction to the inability 

 of mice, rats, rabbits, or dogs to do so.^^^ 



Other uiuisual sources of ergosterol in nature include cocks foot grass, ^'^ 

 wheat germ oil,"^ and Scopolia root sterols."^ Rosenberg^'^^ recorded 

 values in Scopolia up to 1.4% of the total sterols. According to Bills, - 

 no pro\ntamin D other than ergosterol has been isolated from vegetable 

 sources, with the exception of 22-dihydroergosterol, which was separated 

 chromatographically from the minor sterols of ergot by Santos Ruiz.^-° 



(b) 7-DehydrocholesteroI . This is believed to be the most common pro- 

 x'itamin D occurring in the higher animals and man. The occurrence of 

 this provitamin D as a contaminant of cholesterol was first demonstrated 

 by Boer et a/."" Moreover, Boer el al.^°-^-^ noted the presence of cholesterol 

 in duck's eggs, which contained as much as 4.5% of this provitamin D.^ 

 \\'hy this should vary from the type of provitamin D in hens' eggs was not 

 determined, but it is presumably related to the nature of the predominant 

 sterol fed. As already recorded, Windaus and Bock^^ observed the pres- 

 ence of 7-deh3"drocholesterol in pig skin. It has been demonstrated in the 

 whelk or the so-called wave-horn snail {Buccinum undatum)'^^'^ as well, 

 although the other two species of snails investigated were found to contain 

 ergosterol. On the l)asis of the high efficacy ratios of vitamin D observed 

 following irradiation of most animal tissues, it has generally been assumed 

 that all the provitamin D in mammahan sources is 7-dehydrocholesterol 

 (provitamin D3). This is true of the commercial cholesterol obtained from 

 dried animal tissues, identified by Bills^ as the spinal cords of cattle, and 

 used by Waddell,'-- as well as of the activated samples of butter, lard, and 

 brain fat studied by Bethke and co-workers. ^^^ J\Ioreo^'er, similar high 

 efficacy ratios were observed by Haman and Steenbock^-'* with irradiated 

 lard and chicken fat, indicating that the provitamin D in these cases is 7- 

 dehydrocholesterol. 



{c) Miscellaneous Provitamins D. Several provitamins D other than 



1" A. PoUard, Biochem. J., SO. 382-386 (1936). 



"8 A. Windaus and F. Bock, Z. phi/siol. Chem., 256, 47-48 (1938). 



119 A. Windaus and F. Bock, Z. physiol. Chem., 250, 258-261 (1937). 



'20 A. Santos Ruiz, Anales real acad. farm., 3, 201-231 (1941); Chem. Abst., 38, 503 

 (1944). 



121 A. G. Boer, J. van Xiekerk, E. H. Reerink, and A. van Wijk, Dutch Patent No. 

 45,849 (June 15, 1939): German Patent No. 678,533 (July 17, 1939); Chem. Abst., 33, 

 8852(1939). 



1" J. Waddell, J. Biol. Chem., 105, 711-739 (1934). 



123 R. M. Bethke, P. R. Record, and O. H. M. Wilder, ./. Biol. Chem., 112, 231-238 

 (19.35). 



'2* R. W. Haman and H. Steenbock, /. Biol. Chem., II4, 505-514 (1936). 



