INTRODUCTION 641 



Ergosterol > Liimisterol2 > Tachysterol^ 



Vitamin D2 > ToxisteroU 



-> Suprasterolo I 



> Suprasterol2 II 



Products Formed on the Irradiation of Ergosterol""'' '^^ 



The substances formed during the activation of the pro\'itamins D are 

 similar, irrespective of the method of activation. None of the steps in the 

 irradiation mechanism is reversible. The names for the several irradiation 

 products were assigned by Windaus, Deppe, and Wunderhch.'^'' The ir- 

 radiation products are well-defined compounds whose structures are defi- 

 nite, and which are well known. The ease with which the provitamins D 

 can be converted to the corresponding vitamins D \'aries with the wave 

 length of the Ught employed in the irradiation, with the physical state of 

 the provitamin, and with the solvent. The best results are obtained when 

 the provitamin D is in solution, especially when the solution is agitated. 

 The efficiency of activation may be increased when a substance is present 

 which protects the vitamin D after it is produced. Temperature has httle 

 effect upon the activation reaction. For a further discussion of the ir- 

 radiation products, and of factors influencing the irradiation reaction, the 

 reader is referred to Volume I, The Lipids, pp. 758 to 770, as well as to 

 Rosenberg ^"^ and to Bills.- 



c. Occurrence of the Vitamins D. In contradistuiction to the wide 

 distribution of the provitamins D, the vitamins D themselves are present to 

 only a hmited extent. '51,152 They are practically absent from the plant king- 

 dom, although significant amounts of the provitamins D do occur in veg- 

 etables. The chief sources of vdtamin D among the plants are in the mush- 

 room and related fungi. Thus, it has been demonstrated in mushrooms grow- 

 ing in the open woods, in the morel or May mushroom {M orchella esculenta) , 

 the edible boletus {Boletus edulis, B. hadius), the chanterelle (Cantharellus 

 cibarius), and the edible turban-top {Helvella mitra (esculenta)). '^^^■^^^ 

 Scheunert and Reschke^"* obser^-ed that there are only insignificant amounts 

 of vitamins D in the edible meadow (button) mushroom {Agaricus (Psal- 

 liota) campestris) grown in dark cellars, although the \ntamin D was found 

 to be present to a somewhat greater extent when the mushrooms were 



i« P. Setz, Z. phrjsiol. Chem., 215, 183-192 (1933). 



'*o A. Windaus, M. Deppe, and W. Wunderlich, Ann., 533, 118-127 (1937). 



'5' E. P. Daniel and H. E. Munsell, U.S. Dept. Agr., Miscell. Pub. No. 275, 1-176 

 (1937). 



'^^ L. E. Booher, E. R. Hortzler, and E. M. Hewston, Vitamin Values of Foods, Chem. 

 Pub. Co., Brooklyn, 1942. 



1" A. Scheunert and J. Reschke, Deut. med. Wochschr., 57, 349-351 (1931). 



1" A. Scheunert, M. Schieblich, and J. Reschke, Z. physiol. Chem., 235, 91-96 (1935). 



