350 V. BLOOD LIPIDS 



These are referred to either as hemoconia, or "blood dust," 1,2 or, more 

 commonly, as "chylomicrons." The latter connotation was the term 

 coined by Gage and Fish. 3 The chylomicrons are 1 micron or less in diam- 

 eter, and it is believed that they are stabilized by protein films. 4 This sup- 

 position is based upon the fact that an aggregation occurs at a pH of 4.7 

 to 5.3, which represents the approximate isoelectric point of the albumins 

 and globulins of the blood plasma. Coalescence of the fat droplets will 

 occur when the acid is sufficiently strong to precipitate the protein, thus 

 destroying the protective film. 



The mechanism by which the lipids other than neutral fats are carried 

 in the blood is not certain. It is possible for the fat-soluble components 

 such as cholesterol and the fat-soluble vitamins to be dissolved in the drop- 

 lets of fat. On the other hand, there is increasing evidence that cholesterol, 5 

 carotene, 6 and the vitamins A 6 are carried, not in the fat fraction, but as 

 coordination compounds where they are in combination with the plasma 

 proteins. Lecithin may likewise be transported as a protein complex; 

 it has long been recognized that this phosphatide is not directly extractable 

 from blood or tissues without a preliminary disruption of its combination 

 with protein. The high relative concentration of lecithin in the corpuscles 

 may indicate that not only does this phospholipid play a role in controlling 

 the permeability of the red cells, but it is also possible that the cells may 

 at the same time function as a mechanism for lecithin transport. Bloor, 7 

 in his comprehensive monograph, has given a most complete discussion of 

 the lipid composition of the blood, together with a consideration of the fac- 

 tors which alter it. 



2. The Nature of Blood Lipids 



The blood lipids consist of fatty acids, neutral fats, phospholipids, and 

 unsaponifiable components including cholesterol, carotenoids, vitamins 

 A, D, E, and K, and other substances in relatively small amounts. 



1 A. Neumann, Wien. klin. Wochschr., 20, 851-853 (1907). 



2 E. Neisser and H. Braeuning, Z. exptl. Pathol. Therap., 4, 747-760 (1907). 



3 S. H. Gage and P. A. Fish, Am. J. AnaL, 84, 1-85 (1924). 



4 S. De W. Ludlum, A. E. Taft, and R. L. Nugent, Colloid Symposium Annual, 7, 

 233-248(1929). 



5 M. A. Macheboeuf, Bull. soc. chim. biol, 11, 268-293 (1929). 



6 J. Gangulv, N. Krinsky, J. W. Mehl, and H. J. Deuel, Jr., Arch. Biochem. Biophys., 

 88, 275-282 (1952). 



7 W. R. Bloor, Biochemistry of the Fatty Acids, Reinhold, New York, 1943. 



