VITAMIN A 249 



showed that in cases where the amount of carotene fed was below the 

 minimal physiological dosage for vitamin A, the blue units did not rise 

 above those of negative controls, while, in the case of all three rats 

 receiving carotene in excess of the minimal dose, higher values in the 

 blue units were noted, with no corresponding changes in the yellow 

 such as would have been the case if carotene had been stored unchanged. 

 In the detailed report of this important development concerning the 

 relationship of carotene to vitamin A, Moore (1930) has cleared up 

 many doubtful points raised by various investigators and has presented 

 apparently convincing evidence that the carotene in plant materials is 

 more or less completely converted into vitamin A in the animal body. 

 Some features of the conversion are summarized by Moore as follows: 



Carotene Vitamin A 



S>Tithesized in plant Stored in animal 



Intensely yellow Almost colorless 



328/i/i absorption band absent 328/i/x absorption band developed 



Greenish blue SbCU reaction at S90/i/t. Vivid blue SbCU reaction at 610- 



630|U/t. 



In this connection Moore remarks that "since carotene and the liver 

 oil vitamin A both give positive results when tested biologically it is 

 unavoidable that recourse to colorimetric data should be made in study- 

 ing the conversion of one into the other." It is noted that the natural 

 yellow color of carotene in chloroform solution compared with the 

 blue color formed when it is dissolved in the same volume of the 

 antimony trichloride reagent has a yellow to blue ratio of about 11 to 1, 

 while the faintly yellow color of cod-liver oil concentrates compared 

 with the intensely blue color of its antimony trichloride reaction has a 

 corresponding ratio of about 1 to 100. Thus when one constituent is 

 present in a given material in predominant amount, the yellow to blue 

 ratio suggests at once whether this constituent is a carotinoid or the 

 almost colorless vitamin, while in the case of equal mixtures a rough 

 working approximation of the probable proportion is afforded. This 

 paper contains a note added in proof as follows : 



"In a recent communication accessible to the present author only after the 

 above paper went to press, Euler and Rydbom (Svensk. Kemisk. Tidskrift, 1929, 

 41, 223) have shown that when rabbits are fed carrots or carrot extracts, a 'pale 

 yellow-colored carotinoid,' and not carotene, is stored in the liver. Although no 

 attempt has been made to identify this 'carotinoid' with the classical vitamin A, 

 it is obvious that this result is in complete agreement with the experimental 

 findings described in the present paper in the case of the rat." 



Evidence along similar lines has also been reported by Wolff, Over- 

 hoff, and van Eckelen (1930) who state that they have demonstrated 



