VITAMIN A 243 



the curve for cod-liver oils appears to be a linear function. They con- 

 cluded that "quantitative comparison of the color values between differ- 

 ent oils or between colorimetric and feeding experiments can only be 

 made at a sufficiently low value so that the dilution curve approaches 

 a linear function, or be made on the unsaponi liable portion." 



Continuing their study of the specificity of the antimony trichloride 

 color reaction for vitamin A, Norris and Church (1930a) obtained 

 dilution curves for five samples of good grade cod-liver oil and one 

 of ratfish liver oil. The intensity of the blue color produced with the 

 different oils was in no case a linear function of the concentration of 

 the oil nor were the type of curve and the deviation from a linear 

 function the same for the different oils. The original paper should be 

 consulted by those concerned with such testing. 



Attempts were made to extract the unsaponifiable substance com- 

 pletely from a saponified cod-liver oil. Chloroform solutions of the 

 unsaponifiable substance representing various dilutions of the original 

 oil when tested with the antimony trichloride reagent gave straight line 

 dilution curves, but a complete extraction of the unsaponifiable matter 

 with no losses was never obtained. 



Probable Relationship of Vitamin A to Certain Plant Pigments. — As 

 the list of materials containing fat-soluble vitamin increased, a certain 

 analogy was noted and first pointed out by Steenbock (1919) between 

 the simultaneous presence of the carotinoid pigment and fat-soluble 

 vitamin in certain foods and their absence in others. Palmer had earlier 

 shown (1915, 1916) that the plant carotinoids are the source of the 

 so-called lipochromes of the higher animals by direct transfer of the 

 pigments of the diet. Experimental work reported by Steenbock and 

 Boutwell (1920) shortly after the preliminary statement of the 

 hypothesis of a relationship between the fat-soluble vitamin and the 

 yellow pigment carotene, showed that yellow corn furnished enough 

 of the fat-soluble vitamin to allow growth at the normal rate to take 

 place in the rat and to make possible reproduction but not rearing of 

 the young; while the feeding of white corn under similar conditions 

 resulted in nutritional failure. Red corn with a white endosperm gave 

 the same results as white corn, while that with a yellow endosperm gave 

 results approximately the same as those from yellow corn. Later papers 

 by the same author and his coworkers furnished many data in har- 

 mony with the theory of a relationship between vitamin A and lipo- 

 chrome pigment. As noted above, fractionation of the unsaponifiable 

 matter from alfalfa hay brought down the fat-soluble vitamin in the 

 carotene-rich fraction. 



