196 CAROTINOIDS AND RELATED PIGMENTS 



hypothesis that the lipochromes are derived pigments, as shown in 

 the quotation given above from her (1898) paper on salmon pigments. 

 The fact is none the less puzzling, however, and offers a very attrac- 

 tive problem for research. There is evidently a physiological factor 

 involved which is characteristic of the species and thus transmitted. 

 Is it an enzyme, possibly an oxidase, in the digestive tract, blood 

 stream or a vital organ, as Gerould (1921) believes to be the case 

 for the carotinoid-free mutant which he has discovered from a nor- 

 mally carotinoid-containing caterpillar? If the carotinoid-free species 

 of animals possess a more highly developed means of oxidizing the 

 carotinoids introduced in their food it should be possible to determine 

 this fact. If the site of this destruction is in the digestive tract the 

 faces of these animals should be devoid of the pigments when the ani- 

 mals are on carotinoid-rich diets. These ideas merely give a hint of 

 the modes of attacking this problem which suggest themselves to the 

 physiological chemist. 



An even more fascinating problem is offered by the fact that the 

 cow and the horse resorb the carotin of their rations to the relative 

 exclusion of the xanthophylls although the latter are the more 

 abundant in their food, whereas the fowl resorbs xanthophylls to the 

 relative exclusion of carotin. The failure of cows to respond to the 

 feeding of xanthophyll and the inability of the hen to transmit appre- 

 ciable amounts of carotin into the egg yolk shows that these results 

 are not to be explained on the grounds that these two species of ani- 

 mals have the power to convert one carotinoid into the other. Palmer 

 and Eckles (1914d) published the results (3f an attempt to determine 

 whether there is a greater destruction of xanthophyll than carotin 

 along the digestive tract of the cow and whether there is any differ- 

 ence between the action of the natural and artificial digestive fluids on 

 these two classes of carotinoids. In general, the results throw very 

 little light on the fate of the carotinoids during digestion although 

 carotin appeared to show a greater stability; the most significant 

 result secured was that bile dissolves amorphous xanthophyll deposits 

 very readily, while carotin residues are taken up very slowly. This 

 may indicate that the xanthophylls are transported to the liver and 

 there become oxidized while carotin, which forms a complex with a 

 blood protein, escapes this fate. Confirmation of the low solubility of 

 carotin in bile is seen in the finding of Fischer and Rose (1913) that 

 the gall stones of cows contain crystallizable carotin. 



No similar studies have ever been undertaken with fowls. The 



