372 VIII. CHOLESTEROL AND RELATED STEROLS 



absorption of fat.^^ In the case of dogs the Hpemic constant (X 100) 

 averaged 36, and varied only from 23 to 50 in individual determinations.^^ 

 A constant relationship likewise exists between cholesterol and the phos- 

 phatide fraction in the blood. Bloor^^ was the first to report that the 

 cholesterol decithin ratio is uniform in human blood, under both normal and 

 abnormal conditions. Peters and Man^'^ partially confirmed the constancy 

 of this ratio when expressed as cholesterol dipid phosphorus; the mean value 

 was 21.6 ± 2.5 when the cholesterol level was 204.6 mg. %. However, 

 some variations were observed in the ratio, especially in the presence of 

 higher blood cholesterol concentrations. Finally, as indicated earlier, the 

 ratio of cholesterol ester to free cholesterol is a rather precise biologic con- 

 stant under normal conditions. Sperry^^ reported an average figure of 

 73 ± 1.4% for this ratio as determined from tests on 91 normal adults. 

 Confirmatory data have been supplied by Peters and Man^^ and by Brun.^^ 



The level of blood cholesterol varies with the species under considera- 

 tion, having the lowest average in the guinea pig, and the highest in the 

 case of man.^'^'' The ratio of cholesterol ester : total cholesterol has also 

 been found to vary with species. Only slight variations are related to age 

 and sex.^°^ In the case of the horse and cow, the figure for the proportion 

 is 0.67, while in the serum of the dog, pig, and goose, it approximates a 

 value of 0.75. 



Moreover, the blood cholesterol levels of different normal animals of the 

 same species show wide variations, so that it is impossible to state a precise 

 value for cholesterol in any species. ^^ Wide variations have likewise been 

 observed in the plasma cholesterol of the same individual at different times. 

 Thus, Bloor^"- recorded an average plasma cholesterol of 80 ± 14 mg. % for 

 one dog, with variations between 60 and 109 mg. % ; in a second animal, the 

 mean value was 133 ± 14 mg. %, and the range varied between 110 and 

 155 mg. %. 



Age is the most important physiologic condition which causes an altera- 



9^ E. F. Terroine, J. physiol. path, gen., 16, 212-222 (1914). 



95 E. F. Terroine, Ann. Set. Nat. Zool. [10], 4, 5-397 (1920). 



9« W. R. Bloor, /. Biol. Chem., 25, 577-599 (1916). 



" J. P. Peters and E. B. Man, /. Clin. Invest., 22, 707-714 (1943). 



9» W. M. Sperry, /. Biol. Chem., 114, 125-133 (1936). 



99 G. Brun, Changes in the Lipide Contents of Serum in Patients with Manic-Depressive 

 Psychosis, H. K. Lewis, London, 1940. 



">» E. M. Boyd, /. Biol. Chem., 143, 131-132 (1942). 



i°i E. Darraspen, R. Florio, and P. Emangard, Compt. rend. soc. hiol., 143, 1419-1420 

 (1949). 



102 W. R. Bloor, J. Biol. Chem., 103, 699-705 (1933). 



