CAROTENOIDS 



SO quickly diluted that the resulting small increase in the blood level 

 could not be detected (see Fig. 33). 



Hours after dosing 



Fig. 33. — Showing the rise in the vitamin A in the thoracic lymph of goats after 

 feeding carotene, (from Goodwin, T. W., and Gregory, R. A. {i948) 43, 505.) 



Krause and Pierce"*^ have demonstrated the intestinal conversion 

 of carotene into vitamin A in rats in which the liver was tied off at the 

 portal vein. In retrospect the explanation of Popper's®^ observation 

 that vitamin A fluorescence sometimes appeared in the intestine before 

 the liver after the oral administration of carotene is now obvious. 



Since these first investigations, many confirmatory reports have 

 been published. Using the same technique as that employed by 

 Goodwin and Gregory, ^ ' Kon and his associates » ». i o o ^nd Alexander 

 and Goodwin ^^^ have confirmed the intestinal conversion in the rat. 

 Other animals in which this conversion have been demonstrated are 

 chicks, 8 »' 1 0. 1 2 sheep »»• 100 and dairy cattle ^ o^, i o 4 



Patel, Mehl and Deuel ^os j^^ve also demonstrated the conversion 

 of cryptoxanthin into vitamin A in the intestinal wall of the chick, 



278 



