302 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



tion of carotene in man by balance experiments carried out by a team 

 organized by the Medical Research Council. Fraps 356 found that, when 

 carotene, dissolved in oil, was fed with a ration containing cottonseed 

 hulls or agar to furnish bulk, the digestibility was approximately the same 

 as that obtained on a corn meal ration. When casein was substituted 

 for corn meal, the apparent digestibility of carotene was increased, as was 

 also the storage of vitamin A in the liver. In spite of considerable evi- 

 dence indicating the superior digestibility of carotene when fed in oil 

 as compared with a fat-free diet, Frey and Wilgus 357 reported that the 

 total potential vitamin A activity of the eggs from pullets receiving alfalfa 

 was about twice that of eggs from birds receiving carotene in oil, and three 

 times that of birds receiving vitamin A from fish liver oil. 



(c) The Effect of Thyroxine and Thiouracil. Not only is the rate of ab- 

 sorption of carotene controlled by thyroxine and thiouracil, but it has also 

 been found that the digestibility of this pigment is a function of the thyroid 

 secretion. Chanda et a/. 251 demonstrated conclusively that the antagon- 

 ism which is known to exist between thyroxine and thiouracil, insofar as 

 metabolic effects are concerned, is also exerted decisively in controlling 

 the absorption of carotene. Not only was it demonstrated that the 

 digestibility of carotene was higher during the administration of thyroxine 

 and lower during the feeding of thiouracil than the coefficient found during 

 the basal period, but it was likewise found that the rate of reappearance 

 of carotene in the stools after a carotene-free diet was retarded if thyroxine 

 was given, and was accelerated when thiouracil was administered. Goats 

 were able to digest carotene more efficiently than were cows. 251 - 358 This 

 difference in digestibility is consistent with the suggestion of Schultze and 

 Turner 359 that the thyroid gland is more active in the goat than in the 

 cow. This variation was likewise borne out by the fact that the increase 

 in digestibility produced by thyroxine was greater in the cow than in the 

 goat, while the inhibition of absorption was greater in the goat than in 

 the cow. 



The comparative effects of the administration of thyroxine and of 

 thiouracil on the digestibility of carotene in lactating cows and goats, as 

 contrasted with those in normal, untreated animals, are given in Table 7. 



356 G. S. Fraps, Arch. Biochem., 10, 485-489 (1946). 



387 P. R. Frey and H. S. Wilgus, J. Nutrition, 39, 517-528 (1949). 



358 R. Chanda, H. M. Clapham, M. L. McNaught, and E. C. Owen, J. Agr. Sci., 41, 

 179-186(1951). 



389 A. B. Schultze and C. W. Turner, Univ. Missouri Coll. Agr., Agr. Expt. Sta., Re- 

 search Bull. No. 892, 1-89 (Aug., 1945). 



