16 NERVOUS SYSTEM. 



as well as physiological differences.' One of these divisions 

 presents the form of fibres, or tubes. This kind of nervous 

 matter is incapable of generating a force or stimulus, and 

 serves onl j as a conductor. The other division is in the 

 form of cells, and this kind of nervous matter alone is capa- 

 ble of generating the so-called nervous force. 



The nervous matter is divided into two great systems, as 

 follows : 



1. The cerebro-spinal system, composed of the brain and 

 spinal cord with the nerves directly connected with these cen- 

 tres. This system is specially connected with the functions 

 of relation, or of animal life. The centres preside over gen- 

 eral sensation, the special senses, voluntary and some invol- 

 untary movements, intellection, and, in short, all of the func- 

 tions that characterize the animal. The nerves serve as the 

 conductors of impressions known as general or special sen- 

 sations, and of the stimulus that gives rise to voluntary and 

 certain involuntary movements, the latter being the auto- 

 matic movements connected with animal life. 



2. The sympathetic, or organic system. This system is 

 specially connected with the functions relating to nutrition, 

 operations which have their analogue in the vegetable king- 

 dom, and are sometimes called the functions of vegetative 

 life. Although this system presides over functions entirely 

 distinct from those characteristic of and peculiar to animals, 

 the centres of this system all have an anatomical and phys- 

 iological connection with the cerebro-spinal nerves. 



The cerebro-spinal system is subdivided into centres pre- 

 siding over movements and ordinary sensation, and centres 

 capable of receiving impressions connected with the special 

 senses, such as sight, audition, olfaction, and gustation. The 

 nerves which receive these special impressions and convey 

 them to the appropriate centres are more or less insensible 

 to ordinary impressions. The organs to which these special 

 nerves are distributed are generally of a complex and pecul- 

 iar structure, and present numerous accessory parts which 



