STORAGE OF CAROTEXOIDS AND OF VITAMINS A 509 



\'itamin A content. The vitamin A content of the ovary varies consider- 

 ably. Values between 0.7 and 27.0 I.U./g. have been recorded for normal 

 chickens. ^^ For a discussion of the vitamin A and carotenoid content of 

 eggs, the reader is referred to page 562. 



(/) Carotenoids and Vitamins A in Higher Vertebrates. The higher 

 A-ertebrates store variable amounts of carotenoids, but these stored pig- 

 ments do not ordinarily constitute an important source of vitamin A. As 

 described earher, it is only in animals which store both carotene and carot- 

 enols (xanthophylls) (Group A), such as man, or carotene but not the carot- 

 enols (Group B), i.e., cattle and horses, that the stored provitamin A may 

 constitute an important source of idtamin A. On the other hand, Group 

 C, which stores neither the carotenoid hydrocarbons nor the carotenols 

 (sheep, goats, and rats), and Group D which stores only carotenols (such as 

 chickens), do not usually ha\'e any source of vitamin A in their tissues 

 other than preformed ^-itamin A. However, it is possible, in the case of 

 Group D, that A-itamin A might arise from cryptoxanthin if the animals 

 had preA-iously received a diet rich in the carotenol, since it is an excellent 

 provitamin A. 



In the higher vertebrate forms, as in the case of the fishes and birds, the 

 liver contains the greatest proportion of carotenoids and of vitamin A. 

 However, exceedingly wide variations are found in the proportion of vita- 

 min A stored in the liver by different species. It is uncertain whether or 

 not the discrepancies observed can be ascribed to variations in diet or to 

 differences in the ability of the several species to store Adtamin A. Karrer 

 and co-workers^^^ reported that no ^ntamin A was present in the livers of a 

 number of mammals, including the following: Bengal tiger {Felis tigris), 

 adult and yomig male Hon (Felis leo), crab-eating raccoon (Procyon can- 

 crivorus), and harbor seal (Phoca vitidina). On the other hand, Jensen 

 and With^*^ demonstrated the presence of Adtamin A in the livers of a 

 number of species of animals including man. The Adtamin A concentra- 

 tion is the highest in the li\'ers of the fishes, followed next by the livers of 

 reptiles and birds, while the lowest values are noted in the livers of the mam- 

 mals. ^^^ Moore^^^ listed the vitamin A content (in I.U./g.) of the livers 

 of mammals as follows: guinea pig, 10; pig, 100; cow, 150; rabbit, 170; 

 rat (wild), 250; sheep, 600; sperm whale, 4,400; bearded seal, 13,000; 

 and polar bear, 20,000. The low value in the guinea pig is ascribed to an 

 inefficient transformation of carotene to A-itamin A. The rabbit, which to- 

 gether ^ith the guinea pig consumes chiefly green food as a source of \\ia.- 

 min A, appears to be more efficient in converting carotene to Adtamin A 

 than is the guinea pig.-^* Bieri,^^i also, found appreciable amounts of 



