CHAP. VIII.] NERVOUS MATTER. 205 



dently of mental influence, is further proved by instances of con- 

 vulsive movements, more or less violent, which are produced by a 

 morbid irritation of the brain or spinal cord. 



The peculiar animal matter, through the agency of which all 

 these phenomena take place, the nervous matter, is found in two 

 forms, the vesicular and the fibrous. The vesicular nervous matter 

 is gray or cineritious in colour, and granular in texture ; it contains 

 nucleated nerve-vesicles, and is largely supplied with blood ; it is 

 more immediately associated with the mind, and is the seat in 

 which originates the force manifested in nervous actions. The 

 fbrous nervous matter, on the other hand, is in most situations 

 white, and composed of tubular fibres, though in some parts it is 

 gray, and consists of solid fibres : it is less vascular than the other, 

 and is simply the propagator of impressions made upon it. 



When these two kinds of nervous matter are united together in a 

 mass of variable shape or size, the body so formed is called a ner- 

 vous centre, and the threads of fibrous matter which pass to or from 

 it are called nerves. The latter are internuncial in their office : 

 they establish a communication between the nervous centres and 

 the various parts of the body, and vice versa ; they conduct the 

 impulses of the centres to the periphery, and communicate the im- 

 pressions made upon the peripheral nervous ramifications to the 

 centres. The centres are the great sources of nervous power, the 

 laboratories in which the nervous force is generated : the mind is 

 more immediately connected with one of them, the brain ; which, on 

 that account, possesses greater physical development, and acquires 

 pre-eminence over the others. The smaller nervous centres are 

 called ganglions ; the larger ones are the brain and spinal cord. All 

 of these are found in the human subject, and in the vertebrate ani- 

 mals. In the invertebrate classes, the centres are ganglia variously 

 disposed, according to the shape and actions of the animals. 



The brain and spinal cord, and the system of nerves connected 

 with them, constitute the cerebro-spinal portion of the nervous sys- 

 tem, which Bichat distinguished as the nervous system of animal life. 

 The nerves of the senses, and those of volition and common sensa- 

 tion, are connected with it, as well as those which are concerned in 

 many of those purely physical nervous actions with which the mind 

 has no connexion. There are very numerous ganglions connected 

 with this system which are conveniently comprehended under the 

 same title. These are, the ganglions on the posterior roots of the 

 spinal nerves, the ganglion of the fifth pair, those of the glosso- 

 pharyngeal and of the vagus. 



