RADIATION AND VITAMINS 327 



PHYSICAL CHEMISTRY OF ACTIVATION 



Morton, Heilbron, and Kamm (61) reported that the disappearance 

 of ergosterol irradiated in dilute sohition bore a linear relation to the 

 time. Unpublished data from this laboratory show, however, that 

 concentrated solutions do not exhibit the linear relationship. It is 

 probably true, and certainly logical to expect, that under no conditions 

 is the time-disappearance curve actually a straight line, for the products 

 of irradiation are numerous and some of them are sufficiently absorptive 

 to act as filters against the remaining unchanged ergosterol. 



The wave-lengths which affect ergosterol are, of course, those which 

 it absorbs. Ergosterol absorbs strongly from 3050 to 2300 A in the far 

 ultra-violet region (Cox and Bills, 21). But it exhibits a little absorptive 

 power beyond these limits in both directions. Wave-lengths as long 

 as 3130 A are known to activate it slightly, and there is reason to believe 

 that still longer waves play a part in the decomposition of ergosterol 

 and/or of its primary irradiation products (Lahousse and Gonnard, 50). 

 The predominance of these longer waves may explain the relatively low 

 efficiency of sunlight in activation. In the experiments of Windaus, 

 Borgeaud, and Brunken (92), Windaus and Borgeaud (91), and Windaus 

 and Brunken (93), white light in the presence of optical sensitizers 

 resulted in definite chemical changes in ergosterol, but not in the forma- 

 tion of vitamin D. Cathode rays (Knudson and C. N. Moore, 48) and 

 radium emanation (R. B. Moore and DeVries, 59) have a moderately 

 effective activating action on ergosterol. X-rays do not activate (Gold- 

 blatt, 26). The few published reports to the contrary are not supported 

 with acceptable bio-assays. Radio waves of high intensity and short 

 wave-length are without action (unpublished investigation). 



The early work of Pohl (63) suggested that activation may involve 

 the addition of energy to the sterol molecule through an electron dis- 

 placement. Measurement of the energy relations was attempted by 

 Kon, Daniels, and Steenbock (49), who ventured a definite computation 

 in ergs. In a similar undertaking, Marshall and Knudson (57) recognized 

 that the measurement of the energy required for activation is complicated 

 by the occurrence of secondary reactions. Bills, McDonald, BeMiller, 

 Steel, and Nussmeier (15) considered that if the energy of activation 

 remains resident in the activated molecule, a determination of the heat 

 of combustion should reveal it. Actually they found no difference in 

 this respect between plain ergosterol and a very potent irradiation 

 product containing over 20,000 international units of vitamin D per mg. 

 It is interesting to observe that provitamin D, which is as important 

 to animals as chlorophyll is to plants in the utilization of light, does not 

 play even a small role in the storage of energy. 



The researches of Kon, Daniels, and Steenbock (49), Webster and 

 Bourdillon (85), and Marshall and Knudson (57) seemed to show that 



