THE TISSUES 77 



This is a fat in which one of the acid radicles is replaced by 

 phosphoric acid linked to cholin. 



( Fatty acid. 

 Glycerol 4 Fatty acid. 



I Phosphoric acid. 



r 



H H 



HO C C- 



H H 



Hydroxyethyl. 



OH 



-^ 



Cholin. 



CH 3 



trimethyl ammonium 

 hydroxide. 



The chief interest of cholin is that it is toxic, and some of 

 the symptoms occurring in degenerative changes of the nervous 

 system may be due to its presence. It is closely allied to 

 muscarin, a very powerful vegetable poison. 



Cholesterin, like the glycerine of ordinary fats, is an alcohol, 

 but it is monatomic C 27 H 45 HO and it is capable of linking 

 with fatty acids. It is very soluble in hot alcohol, and crys- 

 tallises out on cooling in characteristic square plates, with a 

 notch out of one corner. 



3. Physiology of Nerve 



The neurons form a most intricate labyrinth throughout all 

 parts of the body, and more especially throughout the central 

 nervous system. Each is brought into relationship with many 

 others by its dendritic terminations, and there is a continued 

 interaction between them, the activity of any one influencing 

 the activity of many others. In this way the constant activity 

 of the nervous system, which goes on from birth to death, during 

 consciousness and in the absence of consciousness, is kept up. 



It is unnecessary and gratuitous to invoke the conception 

 of automatic action on the part of any portion of the nervous 

 system. Throughout life these neurons are constantly being 

 acted upon from without, and activity once started by any 

 stimulus sets up a stream of action which may be co-existent 

 with life. 



