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CHAPTER VIII. 



INNERVATION. EXAMPLES OF NERVOUS ACTIONS. NERVOUS MATTER, 



ITS CHEMICAL AND ANATOMICAL ANALYSIS. THE FIBROUS AND 



VESICULAR NERVOUS MATTER. THE NERVOUS SYSTEM. THE 



NERVES, CEREBRO-SPINAL AND SYMPATHETIC. THE NERVOUS CEN- 

 TRES. NERVES AND NERVOUS CENTRES IN INVERTEBRATA. 



DEVELOPMENT AND REPRODUCTION OF NERVES. 



THE function of innervation is effected through the medium of 

 the nervous system, which, ramified throughout the body, and 

 connected with and passing between its various organs, serves 

 them as a bond of union with each other, as well as with the 

 sentient principle of the animal. The mind of man influences his 

 corporeal organs through the instrumentality of this system, as 

 when volition or emotion excites them to action ; and, on the other 

 hand, certain changes in the organs or textures of the body may 

 affect the mind through the same channel, as when impressions made 

 upon them excite mental perceptions. In this way the nervous 

 system becomes the main agent of what has been called the life 

 of relation ; for without some channel for the transmission of the 

 mandates of the will to the organs of motion, or some provision for 

 the reception of those impressions which external objects are capable 

 of exciting, the mind, thus completely isolated, could hold no com- 

 munion with the external world. 



The nervous system, however, can act independently of mental 

 influence. A material or physical change in the nervous substance, 

 unconnected with any affection of the mind, is capable of exciting 

 the action of nerves, and consequently of those organs which are 

 subject to their influence. Some kind of molecular change in the 

 nervous matter is all that is at any time required for the deve- 

 lopment of its peculiar power ; and it is as easy to conceive that 

 this alteration may result from some organic cause, as from mental 

 influence. Of this kind, no doubt, are all those nervous actions 

 with which are associated the functions of the life of the individual, 

 or, in the language of Bichat, of organic life; an essential charac- 

 ter of which is, that they are completely removed from the influence 

 of the will. 



