456 NERVOUS SYSTEM , 



composed of fibres. This kind of nervous matter is incapable of gen- 

 erating a force or impulse, and it serves only as a conductor. The 

 other division is composed of cells, and this kind of nervous matter, 

 while it may serve as a conductor, is capable of generating the so-called 

 nerve-force. 



The nerve-fibres and cells are also 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 centres. This 

 system is specially connected with the functions of relation, or of ani- 

 mal life. The centres preside over general sensation, the special senses, 

 voluntary and some involuntary movements, intellection, and, in short, 

 all functions that characterize the animal. The nerves serve as the 

 conductors of impressions known as general or special sensations and 

 of the stimulus that gives rise to voluntary and certain involuntary 

 movements, the latter being the automatic movements connected with 

 animal life. 



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

 connected with functions relating to nutrition, operations that have their 

 analogue in the vegetable kingdom and are sometimes called the func- 

 tions of vegetative life. Although this system presides over functions 

 distinct from those characteristic of and peculiar to animals, the centres 

 of this system all have an anatomical and physiological connection with 

 the cerebro-spinal nerves. 



The cerebro-spinal system is subdivided into centres presiding over 

 movements and ordinary sensation and centres capable of receiving 

 impressions connected with the special senses, such as vision, audition, 

 olfaction and gustation. The nerves receiving these special impressions 

 and conveying them to the appropriate centres are more or less insensi- 

 ble to ordinary impressions. The organs to which these special nerves 

 are distributed usually are of a complex and peculiar structure ; and 

 they present accessory parts that are important and essential in the 

 transmission of the special impressions to the terminal branches of the 

 nerves. 



The physiological division of the nervous system into nerves and 

 nerve-centres is carried out as regards the anatomical structure of these 

 parts, although they are connected together in the so-called neuron. 

 The two great divisions of the system, anatomically considered, are 

 nerve-cells and nerve-fibres. 



The cells of the nerve-centres, while they may transmit impressions 

 and impulses, are the only parts capable of generating impulses; and 

 as a rule they do not receive impressions in any other way than through 



