Cxxiii. the Absorption Spectrum of Vitamin A. by Richard Alan Morton and Isidor Morris Heilbron

THE absorption spectrum of cod-liver oil possesses a quite special interest because of the fact that the oil contains three known important substances which are sensitive towards light, namely, vitamin A, ergosterol or provitamin D and vitamin D itself. A number of workers have studied the absorption spectrum of the medicinal oil, and Schlutz and his colleagues [1925, 1926] and Heilbron, Kamm and Morton [1927,1] agree that selective absorption occurs in the regions 320-328,Lu and 270-29Ou,u. Woodrow [1928], using a photoelectric spectrophotometer, has been able to find not only a band at about 320,u, but has also recorded the three absorption bands of ergosterol in thin films of the oil. The latter observation is of special interest as demonstrating the extreme sensitiveness of the spectroscopic method under favourable conditions. Even the cholesterol fraction from cod-liver oil contains only about 1 part in 4000 of ergosterol, and the proportion of cholesterol in the cod-liver oil is only some 0 5 %. Moreover, Woodrow's work definitely shows that the absorption band near 270-290,u, is sometimes, if not necessarily, associated with provitamin D. Nearly two years ago we adopted the following working hypotheses: (a) that provitamin D should show selective absorption in the near ultra-violet; (b) that vitamin A should show selective absorption in the nearer ultraviolet, since it has been demonstrated by many workers, e.g. Peacock [1926], that vitamin A may be destroyed by sunlight or the light from an incandescent lamp, and especially by the radiation from a quartz mercury lamp. The first hypothesis was confirmed by a spectrographic study of cholesterol from brain or from cod-liver oil. Three absorption bands were shown to be a criterion of provitamin D and full use of these observations has been made in the later work by various authors on the photochemical conversion of ergosterol into vitamin D. In order to test the second hypothesis, it has been necessary to collect samples of materials varying widely in respect of the proportion of vitamin A present. Since cod-liver oil remains the best-known source of the growth-promoting factor, it seems reasonable to test the assumption that the selective absorption at 320-328,u is connected with the vitamin. In most medicinal oils it is only