314 THE VITAMINS 



Vitamin D absorbs in the same wave-length region as ergosterol and is 

 destroyed by light of the same wave-length as that which forms it. The 

 highest concentration of vitamin D which can be produced by direct 

 irradiation of ergosterol is 35 per cent. This is an absolute maximum 

 and the probable value is lower. The quantum efficiency is 0.3 molecules 

 of vitamin D per quantum of light absorbed." 



Just as this chapter was being completed (October, 1930) two im- 

 portant papers from Bourdillon, Webster, and their coworkers (Askew, 

 Bourdillon, Bruce, Jenkins, and Webster, 1930, 1930a) appeared which 

 can be quoted only in summary. 



In the first paper "a method is described for the partial separation 

 of the irradiation products of ergosterol, by distillation and fractional 

 condensation in a high vacuum. By double distillation, followed by 

 crystallization from aqueous alcohol, a crystalHne product has been 

 obtained, showing high antirachitic power, and a melting point of 113° 

 to 115°. It is not suggested that these crystals are pure vitamin D. They 

 may consist of an inactive substance contaminated with an extremely 

 active vitamin, or of crystalline vitamin forming mixed crystals with an 

 inactive substance. It is possible, on the other hand, that several anti- 

 rachitic substances are formed by the irradiation of ergosterol, and that 

 the cr\-stals are a relatively pure specimen of one of these substances. 

 Some evidence is given as to the degree of efficiency of the process of 

 fractional condensation in a high vacuum." 



The second paper reports a study of the effects of a second irradia- 

 tion by short waves on the substances formed by a first irradiation of 

 ergosterol by long waves. 



"The results show that the product with high absorption at 280 ///z 

 is not vitamin D as previously suggested. The substance with high 

 absorption at 280 jdix can be formed by the action of short-wave radia- 

 tions on some product of a previous action of long waves on ergosterol. 

 Reasons are given for supposing that the initial effect of long-wave 

 radiation on ergosterol is the simultaneous production of at least two 

 substances, only one of which is vitamin D." 



Effects and Measurement of the Antirachitic Factor 



The Line Test. — In the course of routine autopsies conducted in 

 AlcCollum's laboratory on all rats dying from any cause in nutritional 

 experiments, evidences of rickets were found in rats which had been 

 fed diverse deficient diets, but particularly in those which had received 

 diets deficient in fat-soluble vitamin (s) or calcium. Some of these faulty 

 diets rendered the cartilage and adjacent portions of the metaphyses of 



