INTRODUCTION AND HISTORICAL DEVELOPMENT 669 



vitamin A. Gillam and Morton**' reported that the higher maxima for the 

 blue color with cod liver oil were at 606 mju before saponification and 620 m^u 

 after this treatment. However, such carotenoids as lycopene,bixin, 

 capsanthin, and fucoxanthin also develop a blue color with antimony tri- 

 trichloride,*' although they are completely devoid of provitamin A activity. 

 They are not present in fish liver oils or in most animal sources of vitamin A. 



The investigation of the nature of vitamin A has been markedly aided 

 by the use of the property of absorption in the ultraviolet portion of the 

 spectrum. It was first reported by Takahashi and his co-workers^" that a 

 relationship obtains between growth-promoting activity and selective ab- 

 sorption in the region of 320 m/x. Morton and Heilbron^* demonstrated 

 that oils rich in vitamin A, as determined biologically, possess a wide area of 

 absorption between 300 and 350 m/z, wdth the maximum at 328 m;x. It was 

 further demonstrated that this property is also retained in the non-saponi- 

 fiable residue of such vitamin- A-rich oils; moreover, it is proportional to 

 the intensity of the antimony trichloride reaction, and disappears at the 

 same rate as in the colorimetric test when the oils are aerated or irradia- 

 ^g(j 22,23 Further proof of the quantitative relationship between the re- 

 sults of biological estimation and those of ultraviolet absorption are given 

 by Drummond and Morton'^* and by Morton, Heilbron, and Spring^^; 

 such data were found to be reliable if the value at 328 mju was not increased 

 by the presence of biologically inert vitamin A decomposition products.-*^ 

 The importance of spectroscopy in relation to the determination of vita- 

 min A is discussed on pages 728 to 733. 



Further stimulus to the isolation of pure vitamin A preparations was 

 given by the demonstration that it could be concentrated by high-vacuum 

 distillation. Although the results were at first unsatisfactory, due to the 

 extensive decomposition, even with pressures as low as 0.01 mm.,*^*^^ Carr 

 and JewelP^ succeeded in preparing an excellent product with a minimum 

 decomposition by distillation in a specially constructed molecular still at 

 pressures below 10~^ mm. The fraction boiling at 137-138°C. had a 

 considerably increased potency. 



M A. E. Gillam and R. A. Morton, Biochem. J., 25, 1346-1351 (1931). 



" H. V. Euler, P. Karrer, and M. Rydbom, Ber., 62, 2445-2451 (1929). 



*" K. Takahashi, Z. Nakamiya, K. Kawakami, and T. Kitasato, Sex. Papers Inst. 

 Phys. Chem. Research Tokyo, 3, 81-148 (1925). 



" R. A. Morton and I. M. Heilbron, Biochem. J., 22, 987-996 (1928). 



" P. R. Peacock, Lancet, 1926, II, 328-330. 



" S. G. Willimott and F. Wokes, Pharm. J., 118, 217-218 (1927); Chem. Abst., 21, 

 3220 (1927). 



" J. C. Drummond and R. A. Morton, Biochem. J., 23, 785-802 (1929). 



■^ R. A. Morton, I. M. Heilbron, and F. S. Spring, Biochem. J., 24, 136-140 (1930). 



26 A. Chevallier and P. Chabre, Bull. soc. chim. biol, 16, 1451-1478 (1934). 



" I. M. Heilbron, R. N. Heslop, R. A. Morton, E. T. Webster, J. L. Rea, and J. C. 

 Drummond, Biochem. J., 26, 1178-1193 (1932). 



M J. C. Drummond and L. C. Baker, Biochem. J., 23, 274-291 (1929). 



2' F. H. Carr and W. Jewell, Nature, 131, 92 (1933). 



