310 THE VITAMINS 



— 195° C. with so little change in effect on the equilibrium mixture 

 of vitamin D and ergosterol that it appears that the temperature co- 

 efficients for both reactions are very small. The product obtained upon 

 irradiation at very low temperatures was somewhat less potent than the 

 average. 



Bills and Brickwedde (1928) had found that if cholesterol were 

 irradiated at the temperature of liquid oxygen ( — 183° C.) it was about 

 one-tenth as active as when irradiated at room temperature, and con- 

 cluded also that the temperature coefficient of the reaction causing the 

 formation of vitamin D is small. 



Webster and Bourdillon (1928), after removing the unchanged 

 ergosterol from their irradiated material by precipitating it with an 

 excess of digitonin, evaporated the filtrate to dryness (to insure pre- 

 cipitation of final traces of ergosterol through concentration) and 

 extracted it with dry ether, in which digitonin and ergosterol digitonide 

 are insoluble. Upon evaporation of the ether extract, they obtained a 

 transparent glassy hard solid, sometimes colorless, sometimes con- 

 taminated with yellow pigment. It was soluble in its own weight of 

 alcohol at 30° C, soluble in ether, chloroform, and light petroleum, but 

 insoluble in water. Its antirachitic activity was high. 



Bourdillon, Webster and coworkers (1929) reported that the ultra- 

 violet irradiation of ergosterol produces three substances in succession. 

 The first (antirachitic substance) shows intense absorption for wave- 

 lengths of 250 to 310 ///I with a maximum absorption at 2S0 fifi. The 

 second shows intense absorption at 240//// and no antirachitic power. 

 The final product shows little or no absorption and no antirachitic power. 

 They give evidence to show that the first substance, formed by irradi- 

 ating a 0.1 per cent solution of ergosterol in absolute alcohol, removing 

 the unchanged ergosterol by digitonin, evaporating, and extracting with 

 ether, is a single substance and probably vitamin D. 



Knudson and Moore (1928, 1929) found that ergosterol exposed to 

 cathode rays with a tube operating at 180,000 to 200,000 volts is acti- 

 vated antirachitically, but not to as great a degree as when exposed to 

 ultra-violet light. They found further that irradiation from a Cooper- 

 Hewitt lamp, operating at 5 amperes and 140 volts on a 220 volt D.C. 

 circuit, at a distance of 18 centimeters, is more effective if continued for 

 15 seconds to 2 minutes than for 30 minutes, and more effective at 

 ordinary temperatures than at the temperature of liquid air. The char- 

 acteristic absorption spectrum of ergosterol is changed similarly both 

 when exposed to ultra-violet light and to high voltage cathode rays, but 

 the manner in which cathode rays produce their antirachitic action does 



