488 V. BLOOD LIPIDS 



for forty-one normal individuals in Great Britain, based upon the findings 

 of Leitner and Moore. 845 Van Bruggen and Straumfjord 846 reported a 

 vitamin A value for thirty-six control subjects on a hospital diet as 44.7 

 microgram per cent (149 I.U.), while Youmans et a 7 . 847 consider any figure 

 for plasma vitamin A in excess of 21 microgram per cent (70 I.U.) as nor- 

 mal. Sinclair 842 reported a value of 21 microgram per cent (70 I.U.) as the 

 lowest normal value for serum vitamin A for adults. Any figure below 

 9 microgram per cent (30 I.U.) is considered to be abnormally low. Popper 

 and Steigmann 848 cited quite high figures for hospital patients. Average 

 values for 2673 determinations on 454 patients were as follows: vitamin A, 

 men, 58 microgram per cent and women, 47 microgram per cent; carote- 

 noids, men, 74 microgram per cent and women, 85 microgram per cent. 

 According to these investigators, considerable significance can be attached 

 to the ratio of vitamin A: carotene. Apparently, a real sex difference 

 exists in this proportion, which was 0.78 for males and 0.57 for females. 



Serum vitamin A is normally quite high in the dog. 849 " 851 Maddock et 

 a 7 . 851 reported values varying between 173 and 355 microgram per cent 

 for the vitamin A value in the serum of normal dogs. 



Wide variations occur in the carotenoid content of the bloods of animals 

 which contain these pigments. In the case of the cow, values as high as 

 1520 microgram per cent have been recorded, 852 when large amounts of 

 carotene are available in the diet, although figures as low as 140 microgram 

 per cent are also recorded during periods when there are no green feeds. 

 In addition to (8-carotene, considerable amounts of the carotenols, zeaxan- 

 thin, lutein, and cryptoxanthin are also present. 107 Rasmussen et al. m 

 reported that the serum carotene level in the horse is 97 ± 78 microgram 

 per cent, while the plasma vitamin A content is only 12.5 ± 3.5 micro- 

 gram per cent. It is believed that the horse converts carotene into vita- 

 min A quite inefficiently. 



b. General Physiological Factors Related to the Level of Serum Carotene 



846 Z. A. Leitner and T. Moore, Lancet, 1946, I, 262-265. 



846 J. T. Van Bruggen and J. V. Straumfjord, J. Lab. Clin. Med., 33, 67-74 (1948). 



847 J. B. Youmans, E. W. Patton, W. R. Sutton, R. Kern, and R. Steinkamp, Am. J. 

 Pub. Health, 34, 368-378 (1944). 



848 H. Popper and F. Steigmann, J. Am. Med. Assoc, 123, 1108-1114 (1943). 



849 S. W. Clausen, W. S. Baum, A. B. McCoord, J. O. Rydeen, and B. B. Breese, 

 Science, 91, 318-319 (1940). 



860 G. E. Wakerlin and W. G. Moss, Proc. Soc. Exptl. Biol. Med., 53, 149-152 (1943). 



861 C. L. Maddock, S. B. Wolbach, and S. Maddock, J. Nutrition, 39, 117-137 (1949). 



862 W. Braun, J. Nutrition, 29, 61-71 (1945). 



853 R. A. Rasmussen, C. L. Cole, and M. J. Miller, /. Animal Sci., 3, 346-350 (1944). 



854 W. J. Dann, Biochem. J., 26, 1072-1080 (1932). 



