THE TISSUES 79 



r Fatty acid. 

 Glycerol J Fatty acid. 



{ Phosphoric acid. 



Cholin. 



H H 



HO C C- 



OH 



- N 



Hydro xyethyl. 



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 inuscarin, a very powerful vegetable poison. 



Cholesterin may also be obtained in considerable amounts 

 from the fatty substance of the white sheath. Like the 

 glycerine of ordinary fats, it is an alcohol C 26 H 43 ,OH and 

 it is capable of linking with fatty acids. It is very soluble in 

 hot alcohol, and crystallises out on cooling in characteristic 

 square plates, with a notch out of one corner. 



The nerve fibres run together in bundles to constitute the 

 nerves of the body, and each bundle is surrounded by a dense 

 fibrous sheath, the perineurium. When a bundle divides, 

 each branch has a sheath of perineurium, and in many nerves 

 this sheath is continued, as the sheath of Henle, on to the 

 single fibres which are ultimately branched off from the 

 nerve. 



2. Physiology. 



1. Inter-relationship of Neurons. The neurons form a 

 most intricate labyrinth throughout all parts of the body, 

 and more especially throughout the central nervous system. 



By their dendritic terminations each is brought into rela- 

 tionship with many others, and hence 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 conscious- 

 ness, is kept up. 



It is unnecessary and gratuitous to invoke the conception 



