390 V. BLOOD LIPIDS 



Calculated as the ratio of free cholesterol to total cholesterol in blood, the 

 average value is given as 0.28. 



Man and collaborators 215 have used a graphical chart to illustrate the 

 relationship between the lipid phosphorus : cholesterol ratio and that of free 

 cholesterol : total cholesterol. This is illustrated in Figure 2, on page 389. 



The values for normal subjects will fall in rectangle 5, in which the ratio 

 of (lipid P - 3.6): cholesterol (1) falls between 0.020 and 0.038, while the 

 proportion of free cholesterol : total cholesterol (2) varies between 0.24 

 and 0.32. In abnormal cases, the values may fall in rectangle 2 (Ratio 1 is 

 high and Ratio 2 is normal), rectangle 3 (both ratios high) or rectangle 6 

 (Ratio 1 is normal and Ratio 2 is high). In some cases, values falling in 

 rectangles 8 or 9 have been recorded. These occur when the blood choles- 

 terol values fall below 100 milligram per cent. The authors state that the 

 chart is not directly applicable under the latter circumstances. 



Turner and Pratt 219 noted that incubation of normal human serum and of 

 that of patients with disease not involving the liver results in a decrease by 

 more than 30% of free cholesterol, without change in total cholesterol. 

 Since this reaction does not occur when the serum is heated to 56 °C. before 

 incubation, it is assumed that the reaction is probably mediated by an 

 enzyme. 



The ratio of cholesterol ester: total cholesterol has been shown by Dar- 

 raspen et al. 220 to vary with species. However, it is fixed for each particular 

 species, with only slight modifications as related to age or sex. In the case 

 of the horse and cow, the value approaches 0.67, while the ratios in the blood 

 serum of dog, pig, and goose approximate 0.75. The ratio for the dog and 

 pig is similar to that found in man. 



4. The Constancy in the Level of Blood Lipids 



(1) Normal Variations in the Blood Lipids in Animals 

 of the Same Species 



It is, of course, recognized that the mean values for the several blood 

 lipids listed in Tables 2 to 6 are obtained as a result of averaging the figures 

 of a number of determinations, which vary widely, on presumably normal 

 individuals. Animals which are apparently normal may have a value for a 

 lipid constituent deviating widely from the generally accepted "normal" 

 figure. 



219 K. B. Turner and V. Pratt, Proc. Soc. Exptl. Biol. Med., 71, 633-637 (1949). 



220 E. Darraspen, R. Florio, and P. Emangard, Compt. rend. soc. biol, 143, 1419-1420 

 (1949). 



