324 BIOLOGICAL EFFECTS OF RADIATION 



shown that ultra-violet rays, acting on the sterol-bearing fats of the skin, 

 produce a form of vitamin D which is similar in antirachitic action to the 

 vitamin D contained in fish oils. The vitamin D produced by the irradia- 

 tion of pure ergosterol has recently been obtained in crystalline form. 



The following resume of studies on the relation of radiant energy 

 to vitamin D consists mainly of excerpts from a larger survey (9) . Several 

 thousand references to papers covering experimental rickets, and the 

 chemistry and physiology of vitamin D, are given in the following 

 specialized reviews: Park (62), McCollum and Simmonds (55), Hess (30), 

 MacLeod (56), Blunt and Cowan (16), Goldblatt (26), Browning (18), 

 Medical Research Council (58), Laurens (52), and Weidlich (87). 



THE DISCOVERY OF ACTIVATION 



Sunshine, like fish oil, is an old remedy for rickets. Its importance, 

 however, was not fully appreciated until Huldschinsky (44, 45), by means 

 of radiographs, clearly demonstrated the healing action of sunlight and 

 of the light from the quartz mercury arc. Hess, Pappenheimer, and 

 Weinstock (31) determined that the effective wave-lengths of light are 

 the shorter ultra-violet waves of the solar spectrum, or the still shorter 

 waves of artificial sources. Goldblatt and Soames (27) discovered that 

 the livers of irradiated rats, when fed to nonirradiated rats, convey some 

 of the virtue of irradiation to the animals which eat them. 



In 1924 Hess and Steenbock independently and almost simultaneously 

 announced the discovery that exposure of edible materials to ultra-violet 

 Ught endows them with antirachitic activity. Hess found that inert 

 oils, namely, cottonseed and linseed, acquired this property of cod liver 

 oil. Steenbock found the same to be true of muscle tissue, mixed feed, 

 and fats. (Cf . refs. 29, 79.) 



A succession of pubhcations by Steenbock and by Hess rapidly 

 expanded the knowledge of activation. The original brief communica- 

 tions were published in eztenso by Steenbock and Black (81), Steenbock 

 and Nelson (83), and Hess and Weinstock (32). These papers, together 

 with several supplementary contributions and the Steenbock (80) patent 

 of 1928, revealed that edible materials in great variety are activatable, 

 and that activation depends upon the same short wave-lengths which are 

 effective directly in the cure of rickets. Furthermore, it appeared that 

 activation is relatively permanent and that it is not a phenomenon of 

 oxidation. The active moiety of irradiated linseed oil was traced to the 

 unsaponifiable fraction, just as in the case of cod liver oil itself. 



Shortly a second stage in the knowledge of activation was reached 

 when it was demonstrated that sterols become antirachitic upon irradia- 

 tion. Hess, Weinstock, and Helman (35) succeeded in activating phyto- 

 sterol and cholesterol, and to a lesser extent, lanolin. Steenbock and 

 Black (82) found that cholesterol which had been specially "purified" by 



