668 VII. VITAMINS A 



progress could be made in its isolation. The vitamin A content of cod 

 liver oil proved to be a poor standard for comparison because of the con- 

 siderable variations in potency which obtain between different samples.^- ^*' 



One of the first attempts at a chemical evaluation of vitamin A was the 

 suggestion of Steenbock and BoutwelP^ as to its relationship to the lipo- 

 chromes. However, probably because of the minute amounts of the vita- 

 min present, Rosenheim and Drummond^^ were unable to demonstrate 

 any correlation between growth-promoting activity and the presence of any 

 particular iipochromes 



The Drummond Watson reaction,'^ which involves the production of a 

 transient purple color when sulfuric acid is mixed with such vitamin-A-rich 

 sources as the liver oils of mammals, fish, and birds, is presumably related to 

 the presence of vitamin A; however, the transitory nature of the color 

 production precludes its use in quantitative measurements. On the other 

 hand, Rosenheim and Dmmmond^* later proposed the use of a chloroform 

 solution of arsenic trichloride for the determination of vitamin A, which is 

 much more practical; arsenic trichloride produces an intense blue color 

 Avith vitamin A, which persists for a sufficiently long period to enable one to 

 make quantitative measurements of its intensity. The reliability of this 

 technic for the colorimetric determination of vitamin A is attested to by the 

 fact that it gives parallel results with growth-promoting activity ; further- 

 more, the reaction ceases when vitamin A is destroyed by oxidation. The 

 extreme sensitivity of this method has rendered it most useful in the 

 quantitative determination of small amounts of vitamin A. 



The Carr-Price method ^^ in current use today is an adaptation of the 

 arsenic chloride reaction. The latter investigators replaced arsenic chloride 

 with antimony trichloride, which they found considerably more stable. 

 A more exact evaluation was made possible by the use of a tintometer for 

 comparison, but this has been replaced by colorimeters or spectrophotome- 

 ters in the more modern technics in which the color intensity at specific 

 Avave lengths is employed as a standard of comparison. 



Although it was soon recognized that carotenes also responded to the 

 antimony trichloride test,^^ the absorption maxima were shown by Euler, 

 Euler, and Hellstrom^^-" to differ, being 590 m^i for carotene and 617 mju for 



3 J. C. Drummond and S. S. Zilva, J. Soc. Chem. Ind., 41, 280-284T (1922). 

 10 S. S. Zilva and J. C. Drummond, J. Soc. Chem. Ind., 4^, 185-188T (1923). 

 '1 H. Steenbock and P. W. Boutwell, J. Biol. Chem., 41, 81-96 (1920). 



12 O. Rosenheim and J. C. Drummond, Lancet, 1920, /, 862-864. 



13 J. C. Drummond and A. F. Watson, Analyst, 47, 341-349 (1922). 



'* O. Rosenheim and J. C. Drummond, Biochem. J., 19, 753-756 (1925). 

 15 F. H. Carr and E. A. Price, Biochem. J., 20, 497-500 (1926). 

 i« B. V. Euler, H. v. Euler, and H. Hellstrom, Biochem. Z., 203, 370-384 (1928). 

 " B. V. Euler, H. v. Euler, and H. Hellstrom, Svensk Kem. Tid., 40, 256-262 (1928); 

 Chem. Ahst., 23, 3013 (1929). 



