THE NATURE OF BLOOD LIPIDS 359 



and 14% of sphingomyelins. The cephalins engage in metabolic activities 

 at a rate proportional to that of the plasma lecithins, as evidenced by the 

 fact that both show a six-fold increase after the administration of stil- 

 bestrol. 



Albrink 57 reported that 70 to 80% of the serum phospholipids of normal 

 patients or of patients with diseases of the liver or biliary tract were of the 

 choline-containing type. Taylor and McKibbin 58 noted that, although 

 variations in the absolute level of phospholipids were observed in different 

 species, the patterns for the distribution of nitrogenous bases were similar 

 in all nine species examined. Thus, 64 to 79% consisted of bases contain- 

 ing choline, while sphingosine nitrogen made up 10 to 21% of the total 

 lipid nitrogen. There was evidence of the existence of non-choline-con- 

 taining phospholipids in plasma. In later studies of Sinclair, 69 in which a 

 different criterion was employed for the estimation of cephalin than in the 

 earlier studies by this investigator, no cephalin could be detected in beef or 

 dog serum, although it could be accounted for in pig, turkey, and human 

 serum. 



The low values for the proportion of plasma cephalins noted in recent 

 work 50-52,59 are in sharp contrast to those reported in the earlier literature. 

 These vary from maximum figures of 47% 60 and 42% 61 to values 62-66 in the 

 range of 20 to 30%. It has been suggested that these high cephalin deter- 

 minations are probably the result of unsatisfactory analytical technics. 50 

 In the new procedure of Taurog et al., bi a much more reliable analytical 

 procedure has been evolved which consists in separation of the phospho- 

 lipids on a magnesium oxide column. 



Little is known as to the importance of sphingomyelin. The values are 

 in fair agreement, being 16%, 51 14%, 56 10%, 61 17% 66 and 19% 62 of the total 

 plasma phospholipid, while Sinclair 52 reported that sphingomyelin com- 

 prises 15% of the total phospholipids in dog serum, and 32% in beef serum. 



On the other hand, cephalins occur to the highest extent and leci- 



57 M. J. Albrink, J". Clin. Invest., 29, 46-51 (1950). 



58 W. E. Taylor and J. M. McKibbin, /. Biol. Chem., 188, 677-683 (1951). 

 69 R. G. Sinclair, J. Biol. Chem., 174, 355-360 (1948). 



60 E. Kirk, /. Biol. Chem., 128, 637-640 (1938). 



61 S. J. Thannhauser, J. Benotti, and H. Reinstein, </. Biol. Chem., 129, 709-716 

 (1929). 



62 B. N. Erickson, I. Avrin, D. M. Teague, and H. H. Williams, /. Biol. Chem., 135 

 671-684 (1940). 



63 C. Artom, J. Biol. Chem., 189, 65-70 (1941). 



64 G. Brante, Biochem. Z., 805, 136-144 (1940). 

 66 G. Blix, Biochem. Z., 805, 129-135 (1940). 



66 A. D. Marenzi and C. E. Cardini, /. Biol. Chem., 147, 371-378 (1943). 



