240 THE VITAMINS 



experiments. Of the color reagents, arsenic trichloride and antimony 

 trichloride proved most satisfactory. It was found that vitamin D appar- 

 ently does not interfere with the test nor give a color reaction. Olive oil 

 and oleic acid interfered with the test, and their use as diluents of 

 cod-liver oil in the color tests is discouraged. Natural pigments in 

 cod-liver oil could not be removed completely by treatment with the 

 charcoal. Decolorized orange rind oil gave a strongly positive test, as 

 well as showing marked activity in animal feeding tests. Another very 

 potent material, as judged by both color and feeding tests, was decolor- 

 ized spinach extract. Positive results were also obtained with decolorized 

 extracts of carrots and yellow corn. 



These authors concluded that the successful application of color 

 tests for vitamin A to pharmaceutical materials and foodstuffs requires 

 the careful observation of a number of precautions, but urged that the 

 tests be tried on as many natural products as possible in order to estab- 

 lish definitely the specificity of the tests. 



As had been noted by Takahashi et al. (1925), Morton and Heilbron 

 (1928, 1928a) reported that oils or concentrates rich in vitamin A 

 exhibit a well marked absorption band with a maximum at about 

 328/ufi; and these latter workers found a paralleHsm between its inten- 

 sity and vitamin activity. Although it has been shown by Bourdillon 

 and coworkers (1929) that marked absorption in this region is also 

 characteristic of dehydroergosterol, a substance unable to serve as 

 vitamin A for the growing rat or to produce the blue color reaction with 

 antimony trichloride. Morton, Heilbron and Spring (1930) found that 

 the band of dehydroergosterol is more complex and much less intense 

 than that for vitamin A, and states that in order to demonstrate from a 

 study of an inactive substance that the band at 328 juju is not due to 

 vitamin A, it is necessary to show that such a substance as dehydro- 

 ergosterol accounts quantitatively for the absorption shown by vitamin 

 A-rich material. 



Drummond and Morton (1929) reported good agreement for a 

 number of oils of marine origin in an extensive comparison of vitamin 

 A determinations by spectroscopic, colorimetric (Carr-Price modifica- 

 tion of Rosenheim-Drummond test) and feeding methods. 



But within the last two years very contradictory evidence has accu- 

 mulated with reference to the specificity of the Rosenheim-Drummond 

 test. Drummond and Morton (1929) believe that for cod-liver oil at 

 least, the color test and the relative intensities of the absorption band 

 (328 yU//) are more accurate measures of vitamin A than the biological 

 tests. Norris and Danielson (1929a) point out that the intensity of color 



