DIGESTION, ABSORPTION, AND DIGESTIBILITY 425 



and xanthophylls (oxycarotenoids) ; man belongs in this group. In Group 

 B, comprising cattle and horses, mainly carotenes accumulate in the tissues. 

 In Group C, in which sheep, goats, rats, mice, and rabbits are classed, neither 

 carotenes nor oxycarotenoids accumulate. Another group of animals, 

 namely the birds, specifically accumulate xanthophylls or oxycarotenoids. 

 No mammals are known to fit in this category. We shall extend Goodwin's 

 classification by referring to the birds as Group D. 



a. Factors Altering the Absorption of ,S-Carotene. A number of condi- 

 tions may alter the rate at which carotene can be absorbed. In the first 

 place, this carotenoid is absorbed with relative difficulty, due to its low 

 solubility, and because it is a hydrocarbon without functional groups in 

 its molecule. Moreover, there is no possibility that /3-carotene can yield 

 smaller and more easily absorbed molecules, by hydrolysis or by oxidation, 

 without permanent destruction of the carotenoid structure. It is true that 

 it can be broken down to vitamin A, which is readily absorbable, but this 

 ceases to represent the absorption of /3-carotene as such. 



Neither /3-carotene nor any other of the fat-soluble vitamins can be 

 absorbed from the stomach; they are chiefly absorbed from the small 

 intestine. According to Shaw and Deuel, ^^ the rate of absorption is a func- 

 tion of the surface area of the animal. Thus, after a massive dose of 

 /3-carotene in cottonseed oil, (8-carotene was absorbed at the rate of 110 jug. 

 per 100 sq. cm. of body surface per hour. Bile is required for the normal 

 utihzation of |8-carotene. Thus, in hepatic dysfunction, such as in obstruc- 

 tive jaundice, no absorption of carotene occurs. ^^ However, Greaves and 

 Schmidt^'' demonstrated that glycodesoxycholic and desoxycholic acids 

 could effect the absorption of carotene in choledochocolostomized rats. 

 The requirement of bile to insure the absorption of carotene in choledo- 

 chocolostomized animals was confirmed by Irvin and co-workers.-^ The 

 clinical observations of Clausen and McCoord,^^ which show a decreased 

 carotene absorption in catarrhal jaundice (infectious hepatitis), also support 

 this conclusion. 



The nature of the solvent for /3-carotene is also of considerable importance 

 insofar as absorption is concerned. Thus, in the case of rats, cats, and 

 chickens on fat-low diets, there is poor absorption of carotene, while it can 

 be readily utilized when incorporated into a fat-containing regimen. The 

 absorption of carotene is increased if it is emulsified with a water solution 



26 R. J. Shaw and H. J. Deuel, Jr., /. Nutrition, 27, 395-401 (1944). 



26 J. D. Greaves and C. L. A. Schmidt, Am. J. Physiol, 111, 502-506 (1935). 



" J. D. Greaves and C. L. A. Schmidt, Am. J. Physiol., Ill, 492-501 (1935). 



^ J. L. Irvin, J. Kopala, and C. G. Johnstone, Am. J. Physiol, 132, 202-209 (1941). 



" S. W. Clausen and A. B. McCoord, /. Pediat., 13, 635-650 (1938). 



