CEREBROSIDES 57 



The approximate amount of lecithin contained in various 

 substances may be seen from the following table : — 



Egg yolk 



Liver 



Blood 



Leguminous seeds 



Cereals 



9*4 per cent. 



2-1 



1-8 

 0-8-I-64 ,, 

 0-25-0-53 .. 



Pure lecithin has not as yet been obtained from vegetable 

 sources, the substances isolated by Winterstein * and his col- 

 laborators from wheat flour and from the seeds of Avena 

 saliva, Lupinus albus, L. luteus, Vicia saliva, from the leaves of 

 MschIms hippocastanum, etc., being mixtures which, moreover, 

 contain a carbohydrate complex. For an account of the 

 methods employed in the extraction of these substances the 

 original papers should be consulted. Smolensky f found that 

 wheat germs (i.e. the embryos which are a bye-product of the 

 flour mills) yielded a phosphatide whose composition was 

 much closer to that of ordinary lecithin than was that ob- 

 tained from the flour. 



Physiological Significance. 



Lipins are, apparently, universally present in living cells 

 and must, presumably, play an important part in the physio- 

 logy of the organism : but what their function may be is 

 unknown and as a consequence many roles have been ascribed 

 to these bodies. 



Overton % showed in many instances that those substances 

 which are soluble in lipins readily enter the cell, whilst those 

 which are insoluble in lipins are absorbed by the cell with 

 difhculty. From such observations he concluded that the 

 plasma membrane is composed essentially of lipins and formu- 

 lated his solution theory of permeability. His views at first 



* Winterstein and Hiestand : " Zeit. physiol. Chem.," 1907, 54, 288 ; 

 Winterstein and Smolensky : id... 1908, 58, 506 ; Winterstein and Steg- 

 mann : id., 1908, 58, 527' See also Schulze and Likiernik : id., 1891, 

 15, 405 ; Schulze : id., 1895, 20, 228. 



t Smolensky : id., 1908, 58, 522. 



t Overton: " Vierteljahschr. Naturf. Ges. Zurich," 1895, 40, 159; 

 1896, 41, 383 ; 1899, 44, 88 ; " Jahrb. wiss. Bot.." 1900, 34, 669. 



