28 INTRODUCTION 



substances in the heart, for example, 60 to 70 per cent, is leci- 

 thin, which constitutes about 8 per cent, of the dry weight of 

 the myocardium. 



There are several varieties of lecithin, depending upon the 

 fatty acid radical they contain, and for the group Koch has 

 proposed the name of ledihans. 



The structural formula of one lecithin, stearyloleyl lecithin, 

 is as follows : 



CH 2 -0-C 18 -H 35 

 CH O C 18 -H330 

 CH 2 O PO OH 



O CH 2 CH 2 N = (CH 3 ) 3 . 

 N>H 



It differs from ordinary fats, therefore, in having two special 

 groups, one the phosphoric acid, the other the cholin radical, 

 which last seems to be of no little importance in pathological 

 processes. In its physical properties it is quite similar to the 

 ordinary fats, although it forms even finer emulsions in water, 

 which are practically colloidal solutions (W. Koch). 



Cephalin, a closely related body differing in having but one 

 methyl group, is also probably as widely spread in the tissues 

 as lecithin, according to Koch and Woods. * 



Cholesterin, which is another lipoid, is nearly as universally 

 present as lecithin. 2 There are probably several varieties of 

 cholesterin, w r hich exist both free and in combination with fatty 

 acids, for cholesterin is an alcohol and not at all similar to the 

 fats chemically, although very similar physically. The empiri- 

 cal formula is C 27 H 44 O (or C^H^O) and it is possibly related 

 to the terpenes. It seems to be quite inert chemically, and 

 therefore is probably important only because of its effect on the 

 physical properties of the cells. By some it is considered to be 

 a decomposition or cleavage product of the proteids, which is in 

 accordance with its abundance in masses of old necrotic tissue, 

 e. g.j atheromatous masses, old infarcts, and old exudates. 



Protagon, which name probably covers a group of nitrogen- 

 ous, phosphorized bodies, (Gies 3 ), occurs in many or all cells, 

 but especially in the nervous tissues. The properties of prota- 

 gon are in general similar to the other lipoid s, but its exact 



1 Jour. Biol. Chem., 1905 (1), 203. 



2 Recent literature given by Abderhalden and Le Count, Zeit. exp. Path, 

 u. Pharm., 1905 (2), 199. 



3 Jour. Biol. Chem., 1905 (1), 59. 



