182 ON VARIABILITY AND ADAPTATION 



exclude the simpler palrnitates and stearates from the causes of 

 the phenomenon in the organism, although the possibility must 

 not be forgotten that bodies like certain of the lecithins which 

 contain both oleic and palmitic or stearic acid radicals, may 

 eventually be found to afford the reaction. 



These considerations, therefore, so far as it is legitimate to 

 carry them, distinctly favour the view that the myelin globules 

 of the organism are probably of the nature of oleic acid com- 

 pounds — are soaps of oleic acid of greater or less complexity. 



It deserves pointing out that from wholly different considera- 

 tions, namely, from the point of view of chemical analyses of 

 myelin-containing substances, the earlier workers have arrived 

 at conclusions which are approximately in harmony with 

 ours. Liebreich, for example, analysing nerve matter, deter- 

 mined that the constituent which was the essential cause of 

 the myelin figure formation — or otherwise the myelin proper — 

 was the protagon which he was the first to isolate. With Apathy, 

 I may add, I have found the myelin figures from nerve matter 

 under certain conditions doubly refractive. Now protagon 

 dissociates into lecithin, fatty acids and neurin or cholin, and 

 while crystalline protagon treated with water merely swells, 

 affording no myelin figures, if a drop of oleic acid under the 

 microscope be acted on by a solution of cholin or neurin, I gained 

 an immediate development of exquisite doubly refractive myelin 

 figures — as exquisite as when strong ammonia acts on oleic acid. 

 It is not therefore the protagon as such, but dissociated cholin 

 oleate or neurin oleate 1 that would seem to be the base of the 

 myelin formation in nerve matter. 



There is another body which separates out abundantly in the 

 alcoholic extraction of nerve matter, namely, cholesterin. This 

 in itself does not afford the intermediate state, but its com- 

 pounds with the fatty acids manifest it, and it is quite possible 

 that such compounds play a part in the myelin formation seen 

 in fresh nerve tissues. We owe to the elder Beneke in 1862 the 

 first recognition of the significance of cholesterin in myelin 

 production. He showed that while olive oil treated with caustic 

 potash afforded myelin bodies, the more cholesterin he added 

 to the oil the better was the result ; that alcoholic extract of 



1 There is still some doubt regarding the identity of cholin and neurin. 

 I have, however, gained a compound of oleic acid with both substances. 



