1906.] 



On the Myelins, etc., of the Organism. 



365 



What, then, is myelin ? We are still unable to state definitely, but 

 believe that the considerations and observations here brought forward lead 

 one step nearer to the solution of the problem. Various conclusions have 

 been reached, from Beneke (who regarded it as a glyceride of cholesterin, and 

 laid clown that " ohne Cholestearin keine Myelinformen "), through Liebreich 

 (who held that while protagon itself might not exhibit myelin forms it would 

 probably be found that where myelin forms developed, there protagon was 

 constantly present), to modern workers upon autolysis (who ascribe the 

 phenomena to lecithin), and lastly, to those who, with Neubauer and Quincke, 

 regard myelin formation as the expression of a physical state common to 

 a very large number of bodies. 



There is one significant fact in this connection, namely, that, so far, the 

 only crystalline fluids known which are in the intermediate state at the room 

 temperature are certain of the oleic acid compounds ; in fact, it may be laid 

 down from our observations that almost all the simpler oleates and some 

 like lecithin, of the more complex are in the fluid-crystalline state at 15° C 

 Lecithin has definitely been determined to be the main constituent of the 

 diffused myelin of normal tissues, and it is interesting to note that all 

 the bodies, with the exception of cholesterin, which have been adduced as 

 the essential constituent of myelin — protagon, lecithin, soaps — are oleic acid 

 compounds, and, as regards cholesterin, Beneke's experiments indicate that 

 he dealt with cholesteryl oleate. It may be that it is wrong to include 

 lecithin in this group. There exist in the organism di-stearo- and stearo- 

 palmito-lecithins, and these are more abundant than is di-oleo-lecithin. 

 While many considerations indicate that oleic acid compounds in particular 

 possess properties most allied to those of the myelins of the organism, we 

 cannot thus absolutely exclude the other fatty acids. We may, however, 

 it would seem, confidently conclude that fatty acid is an essential constituent 

 of " myelin," and that of the fatty acids oleic acid plays the most important 

 part. 



Is it possible to proceed any further ? The evidence at our disposal 

 appears to point to at least two different varieties of myelin, one in which 

 cholesteryl oleate is the essential constituent, another in which we have 

 essentially to deal with cholin oleate. 



Examining the aorta of a middle-aged man, we found in the thoracic 

 portion a single atheromatous area, affecting the middle as well as the inner 

 coat. This afforded a small amount of dry atheroma material. Upon 

 making a smear of this, while it showed abundant and large plates of 

 cholesterin, and abundant fatty globules, there was not a single doubly 

 refracting globule present. Upon warming the slide gently over the flame and 



VOL. LXXVIII. — 15. 2 F 



