II. CHEMISTRY 175 



wavelength also appears to be the upper limit for T-dehydrocholesterol.^"^"^"* 

 There is reason to believe that still longer waves play a part in the decompo- 

 sition of ergosterol and /or of its irradiation products. ^^^ The predominance 

 of these longer waves may explain the relatively feeble effect of sunlight 

 in activation. White light in the presence of optical sensitizers produces 

 chemical changes in ergosterol, such as peroxide and pinacol formation, but 

 it does not produce vitamin D.^''^ 



Ergosterol in the form of vapor, spray, powder, or solution can be ac- 

 tivated by a high-frequency oscillating discharge, with or without elec- 

 trodes.^"*'-^" High-voltage direct current has also been claimed to be effec- 

 tjyg 209 gome activation is induced by cathode rays^^^-^io^. and by radium 

 emanation. 211 X-rays apparently do not activate it.^^^ 



In an early (1927) study of the disappearance of ergosterol during irra- 

 diation in dilute solution, Morton et al}'^^ concluded that the time-disappear- 

 ance curve is a straight line. They measured the disappearing ergosterol 

 spectrographically and did not know at the time of the existence of the 

 intermediate products of irradiation which contribute irrelevant absorption 

 to the system. Bourdillon el al}^^ measured the disappearance by digitonide 

 precipitation and found that the rate slows down as the irradiation proceeds. 

 The problem was finally resolved by Dasler^^^ in 1938. He found that the 

 time-disappearance curve had the shape of a first-order curve. The reaction 

 involving the disappearance was, however, apparently a zero-order reac- 

 tion, because the half-life of the ergosterol was directly proportional to the 

 initial ergosterol concentration. The first-order character of the curve was 

 explained by the fact that increasing amounts of light were filtered out by 

 the piling up of light-absorbing irradiation products. 



Before the structure of vitamin D was known, PohP* suggested that 



203 J. W. M. Bunker, R. S. Harris, and L. M. Mosher, /. Am. Chem. Soc. 62, 508 (1940). 



"■i A. F. Hess and W. T. Anderson, Jr. J. Am. Med. Assoc. 89, 1222 (1927). 



2" C. Sonne and E. Rekling, Strahlentherapie 25, 552 (1927). 



20* Lahousse and Gonnard, J. phys. radium, Ser. 6, 10, 114S (1929). 



^"7 A. Windaus, P. Borgeaud, and J. Brunken, Nachr. Ges. Wiss. Gottingen, Math, 

 physik. Kl. 313 (1927); A. Windaus and P. Borgeaud, Ann. 460, 235 (1928); A. Win- 

 daus and J. Brunken, Ann. 460, 225 (1928). 



208 N. A. Milas, U. S. Pat. (Reissue) 22,038 (1942). 



209 1. G. Farbenindustrie, Austrian Pat. 119,210 (1930). 



210 C. C. Whittier, U. S. Pats. 2,106,779, 2,106,780,2,106,781,2,106,782 (1938); W. 

 Dasler and C. D. Bauer, J. Biol. Chem. 167, 581 (1947). 



2ioa A. Knudson and C. N. Moore, /. Biol. Chem. 81, 49 (1929). 



211 R. B. Moore and T. DeVries, J. Am. Chem. Soc. 53, 2676 (1931). 



212 H. Goldblatt, Ergebn. allg. Pathol, u. pathol. Anal. 2. Abt. 25, 58 (1931). 



213 R. A. Morton, I. M. Heilbron, and E. D. Kamm, J. Chem. Soc. 1927, 2000. 



21* R. B. Bourdillon, C. F. Fischmann, R. G. C. Jenkins, and T. A. Webster, Proc. 



Roy. Soc. (London) B104, 561 (1929). 

 216 W. Dasler, Summaries of Doctoral Dissertations Univ. Wisconsin 3, 219 (1938). 



