424 IX. CAROTENOIDS AND VITAMINS A 



deal chiefly with the chemistry and, to a lesser extent, with the physiologic 

 action of the carotenoids are those of Palmer,-^ of Zechmeister,-- of Lederer^* 

 and that of Karrer and Jucker.^^ An extensive treatment of the subject of 

 the carotenoids and vitamins A, chiefly from a chemical viewpoint, is 

 included on pages 507 to 738 of Volume I of this series of monographs. 



2. The Digestion, Absorption, and Digestibility of Carotenoids and 



of the Vitamins A 



(/) ^-Carotene and Other Carotenoids 



Since /3-carotene is the most widely distributed and best known carote- 

 noid, as well as that of greatest physiologic importance, more informa- 

 tion is available concerning the digestion and absorption of this compound 

 than can be found in the case of the other carotenoids. There is consider- 

 able evidence that /3-carotene can be absorbed as such, transported in the 

 lymph and blood, stored in the liver and other tissues, and excreted in the 

 milk by some species of animals. It is a well-recognized fact that the color 

 of milk and of the butterfat derived from it is chiefly determined by the 

 quantity of carotene in the diet of the lactating animal. The same situa- 

 tion obtains in relation to the pigmentation of hens' eggs, although carote- 

 noid pigments other than /3-carotene are likewise involved. In the case 

 of man, jS-carotene is a normal component of the blood, but here again the 

 amount present is related to the intake of the provitamin. Thus, when 

 large amounts are ingested over a period of time, a condition known as 

 carotenemia occurs in man. Abnormally high quantities of the chromogen 

 are present in the blood; as a result considerable amounts are 

 also deposited in the tissues. In sharp contrast to the aforementioned 

 examples, the blood, liver, or other tissues of certain animals, such as the rat, 

 goat, and pig, do not contain appreciable amounts of i8-carotene or of 

 carotenoids. 



Goodwin 2° classified mammals into three groups according to the mecha- 

 nism by which the carotenoids are metabolized. In Group A the tissues 

 accumulate indiscriminantly both carotenes (hydrocarbon carotenoids) 



^^ L. S. Palmer, Carotenoids and Related Pigments, Chem. Catalog Co., New York, 

 1922. 



22 L. Zechmeister, Carotinoide, Springer, Berlin, 1934. 



25 E. Lederer, Recherches sur les Carotenoids des Animaux inferieurs, et des Crypto- 

 games, Lons-de-Saumier, Paris, 1937, pp. 5-93; cited by D. L. Fox, Carotenoid and 

 Indolic Biochromes of Animals, Ann. Rev. Biochem., 16, 443-470 (1947), pp. 448, 454, ff. 



2* P. Karrer and E. Jucker, Carotinoide, Birkhauser, Basle, 1948; Translated and 

 revised by E. A. Braude, Elsevier, New York, 1950. 



