312 THE VITAMINS 



They also reported that a freely transparent solvent is not always 

 required, for extremely high activation can be obtained in arachis 

 oil. 



Windaus and Linsert (1928) showed that when ergosterol is dis- 

 solved in alcohol, ether, ethyl acetate, benzene, or cyclohexane and 

 irradiated, there is a change in its optical activity from negative to 

 positive. It was later shown by Windaus and coworkers (1929) that 

 when the optical rotation becomes positive, the product of irradiation 

 is no longer active antirachitically. 



Windaus and Linsert (1928) also reported a change in the ultra- 

 violet absorption spectra and an increase in solubility with irradiation 

 and showed that the molecular weight of the irradiated ergosterol, which 

 was freed from the unchanged ergosterol by precipitation with digitonin, 

 is the same as that of the unirradiated ergosterol. Their results indicate 

 that the alcohol group in ergosterol does not disappear or the number of 

 double bonds change with irradiation. These investigators point out that 

 on irradiation there may be a shifting of the double bonds inside the 

 ergosterol molecule ; or that a stereo-change in the secondary alcohol 

 group may occur, since the irradiated ergosterol is not precipitated by 

 digitonin. 



Rosenheim and Adam (1929) found that the monomolecular surface 

 films on water of ergosterol and of the three products formed from it on 

 irradiation, as described by Bourdillon, Webster, et al. (1929), showed 

 a resemblance to those of certain ketonic cholesterol derivatives. The 

 product having an absorption band at 280 ///f (probably vitamin D) 

 resembled that of oxycholesterylene. This compound, however, has no 

 antirachitic properties before or after irradiation. They consider it at 

 present impossible to decide which constituent of the mixture containing 

 the active substance represents the vitamin. Alternative possibilities are 

 that the vitamin may be a ketone itself or that the highly absorptive 

 unsaturated ketone may constitute the biologically inactive portion of the 

 mixture, the vitamin itself being in the remaining portion in minute 

 amounts only. It is thought that if the latter explanation proved to be 

 the correct one the vitamin is one of the ergosterol derivatives resulting 

 as by-products in the ketone formation. In either case the lability of the 

 hydrogen of the CH(OH) group is considered to be the control- 

 ling factor of the changes induced by ultra-violet irradiation of ergo- 

 sterol. 



Reerink and Van Wijk (1929, 1929a), by the use of suitably selected 

 light sources and filters, irradiated hexane solutions of ergosterol in 

 quartz tubes and studied the progress of the reaction at different wave- 



