II. CHEMISTRY 



181 



The quantity of any one irradiation product present after a given period 

 xaries with the conditions of exposure, and correspondingly there is a vari- 

 ation in the spectral picture of the total mixed products. As explained 

 above, the wavelength is a factor, particularly important in the accumula- 

 tion of lumisterol and tachysterol. Temperature appears to be important 

 in the accumulation of precalciferol. The specific solvent effect is a factor 

 in the accumulation of toxisterol. 



The presence of dissolved oxygen in the solvent markedly affects the 

 spectral picture of activation .-^^'^ It does so by altering the by-products of 



220 240 260 280 300 320 



220 240 260 280 300 320 220 240 260 280 300 



Fig. 11. Spectral changes during irradiation of ergosterol in alcohol by quartz 

 mercury lamp. Compare Fig. 12. (After Bills et al^^^) 



activation, rather than by affecting to any large extent the formation or 

 destruction of vitamin D.'^^ In one study ,2"*" extreme freedom from oxygen 

 during the irradiation of ergosterol did not occasion any enhancement of 

 antiricketic potency. The products of oxidation make difficult the crystal- 

 lization of vitamin D,-^^ and are therefore especially to be avoided when 



"88 A. Smakula, Nachr. Ges. Wiss. Gottingen, Math, phijsik. Kl. 49 (1928); C. E. Bills, 



E. M. Honeywell, and W. M. Cox, Jr., /. Biol. Chem. 80, 557 (1928) ; E. H. Reerink 



and A. van Wijk, Biochem. J. 23, 1294 (1929). 

 "9 C. E. Bills, E. M. Honeywell, and W. M. Cox, Jr., J. Biol. Chem. 80, 557 (1928). 

 2^° H. H. Beard, R. E. Burk, H. E. Thompson, and H. Goldblatt, J. Biol. Chem. 96, 



307 (1932). 

 2" T. C. Angus, F. A. Askew, R. B. Bourdillon, H. M. Bruce, R. K. Callow, C. F. 



Fischmann, J. St. L. Philpot, and T. A. Webster, Proc. Roy. Soc. (London) B108, 



340 (1931). 



