IV. DETERMINATION 97 



Snow^^ describe a modified procedure with glycerol dichlorohydrin to de- 

 termine the vitamin A level in blood and serum. The vitamin A and carotene 

 content in feces can be determined by the method of With.''' The same 

 author discusses in detail investigations on the range of error of the "blue 

 value disturbance" by carotene with the Carr-Price reaction. But one should 

 be reminded that statements about the vitamin A and carotene content of 

 blood and blood serum represent in most cases only approximate values. 

 Only a few of the great number of methods proposed for the examination of 

 tissue, especially liver samples, can be mentioned. '^■i'"' In most cases they 

 differ only in the preparation of the testing material. The procedure pub- 

 lished by Glover, GoodAvin, and Morton^*" • ^°- permits the determination of 

 esterified vitamin A, free vitamin A, and carotene simultaneously. With'"' 

 has worked out a micromethod for the vitamin A determination in liver 

 samples taken at biopsy. The vitamin A and carotene content in milk, butter, 

 and margarine is determined exclusively after saponification.^^ For the 

 examination of eggs a series of methods has been elaborated. The conditions 

 are here more complicated in that the main part of the carotenoids does 

 not consist of the biologically active carotene but of the inactive xantho- 

 phyll, zeaxanthin, and others. In such cases the isolation in pure state by 

 chromatographic adsorption is indispensable. Corresponding methods were 

 worked out by Gillam and Heilbron,'"^ Thompson and collaborators,^* 

 Mann,-^ and Schrenk et al.-^ Narod and Verhagen'"^ have elaborated a 

 procedure for the determination of vitamin A in foodstuffs which have been 

 artificially vitaminized. 



B. BIOLOGICAL METHODS FOR THE DETERMINATION OF 

 VITAMIN A ACTIVITYio«-i"7 



Rats are used nearly exclusively for biological assays. According to 

 Coward,'"^ male rats are more sensitive to vitamin A deficiency than are 



"^ H. Veldman, Ada Brevia Neerl. Physiol. Pharmacol. Microbiol. 11, 178 (1941). 



" A. E. Sobel and S. D. Snow, J. Biol. Chem. 171, 617 (1947). 



" T. K. With, Z. Vitaminforsch. 11, 298 (1941). 



»8 H. B. Jensen and T. K. With, Biochem. J. 33, 1771 (1939) ; Vitamine u. Hormone 3, 



254 (1943). 

 " F. Harms, Vitamine v. Hormone 2, 151 (1942). 



<"> W. D. Gallup, J. A. Hoefer, Ind. Eng. Chem. Anal. Ed. 18, 288 (1946). 

 «i J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. J. 41, 94, 97 (1947). 

 02 T. W. Goodwin and R. A. Morton, Analyst 71, 15 (1946). 

 °^ T. K. With, Biochem. J. 40, 249 (1946). 



0* A. E. Gillam and J. M. Heilbron, Biochem. J. 29, 1064 (1935). 

 " M. Narod and D. Verhagen, Anal. Chem. 20, 627 (1948). 

 "* N. T. Gridgeman, The Estimation of Vitamin A. Lever Brothers and Uni Lever 



Ltd., London, 1944. 

 " E. M. Nelson and J. B. de Witt, Biol. Symposia 12, 1 (1947). 

 «» K. H. Coward, Brit. Med. J. I, 435 (1942). 



