362 V. BLOOD LIPIDS 



sine, 20% ; sugar, 40 to 41%. The sugar was found to consist of galactose, 

 glucose, and chondrosamine. It is believed to be derived from the stroma 

 of the red blood cells. 



(5) Free Fatty Acids 



Kelsey and Longenecker 22 found that beef plasma contained 28.4 milli- 

 gram per cent of free fatty acids, which accounted for 10.7% of the total 

 lipids. There is some question as to whether the free fatty acids are actu- 

 ally present in blood, or whether they originate during the analytical pro- 

 cedures. Fairbairn 84 demonstrated that the proportion of free fatty acids 

 in tissues is minimal, but that it increases immediately, on removal of the 

 tissue from the animal, by hydrolysis of the phospholipids. 



(6) Unsaponifiable Components 



The unsaponifiable fraction of the blood is composed largely of chole- 

 sterol. Anderson 85 reported that, in beef plasma, the unsaponifiable frac- 

 tion consisted almost entirely of cholesterol, although the animals had re- 

 ceived exclusively phytosterols in their food. In the case of dog plasma, 

 this fraction was found to be more complex. Cholesterol could not be 

 prepared from it, although all but 18% was precipitated by digitonin. 

 About 37% of the total unsaponifiable fraction could not be identified. In 

 addition to the cholesterol, in some species, the unsaponifiable fraction will 

 contain /3-carotene or carotenoids, while vitamins A, D, and E will appear 

 in this fraction in all cases. 



In the case of human serum, Dimter 86 obtained a total lipid content of 

 360 milligram per cent, of which 66% consisted of the unsaponifiable frac- 

 tion. About two-thirds of the non-saponifiable fraction was precipitable 

 with digitonin. In the cholesterol-free portion of the unsaponifiable frac- 

 tion, evidence was adduced for the presence of a cholesterol precursor as 

 well as of an aliphatic alcohol. However, no hydrocarbons of the squalene 

 type could be identified. Koehler and Hill 87 reported the presence of 7- 

 dehydrocholesterol in appreciable quantities in human serum. The total 

 concentration of 7-dehydrocholesterol in the free form was found to vary 

 between 1.8 and 7.0 milligram per cent, while the range of this sterol in com- 

 bined form for thirty-five subjects was from 2.4 to 35 milligram per cent. 



84 E. Fairbairn, J. Biol. Chem., 157, 645-650 (1945). 



85 R. J. Anderson, J. Biol. Chem., 71, 407-418 (1926). 



86 A. Dimter, Z. physiol. Chem., 272, 189-200 (1942). 



87 A. E. Koehler and E. Hill, Federation Proc, 12, 232-233 (1953). 



