528 OF THE NERVOUS SYSTEM AND ITS ACTIONS. 



fications. The peculiar connexion of this system of nerves with the 

 organs of vegetative life, has caused it to receive the designation of the 

 Nervous System of Organic Life ; the Cerebro-Spinal system being 

 termed the Nervous System of Animal Life. It is also not unfrequently 

 termed fas ganglionic system ; on account of the separation of its centres 

 into scattered ganglia, which forms a striking contrast to the concentra- 

 tion that is so evident in the Cerebro-spinal system. But this term is 

 objectionable, as leading to a supposed analogy between this system and 

 the general nervous system of Invertebrata, whose centres are equally 

 scattered ; an analogy which is completely erroneous, since, as we have 

 seen, this last is chiefly the representative of the Cerebro-Spinal system 

 of Vertebrated animals. The term Sympathetic is perhaps the best ; 

 although it must not be supposed that this system of nerves is the 

 instrument of by any means all the sympathies, which manifest them- 

 selves between different organs. 



927. The Sympathetic system contains both classes of nervous fibres ; 

 the ordinary white tubular fibres, all of which are probably derived 

 from the Cerebro-Spinal system ; and the gray or gelatinous fibres, part 

 of which seem to belong to itself ( 375). Thus we may consider each 

 system as intermingling itself with the other ; the Cerebro-Spinal sys- 

 tem transmitting some of its fibres, both motor and sensory, into the 

 Sympathetic ; whilst the Sympathetic is represented in the Cerebro- 

 Spinal system, by certain fibres and collections of vesicular matter of 

 its own. The trunks that proceed from the Semilunar ganglia, are 

 almost entirely composed of gray or organic fibres ; whence it is evident 

 that these ganglia are to be regarded as the true centres of the Sympa- 

 thetic system. On the other hand, the trunks which issue from the 

 chain of spinal ganglia, contain a large admixture of white or tubular 

 fibres. 



928. The Sympathetic nerves possess a certain degree of power of 

 exciting Muscular contractions, in the various parts to which they are 

 distributed. Thus by irritating them, immediately after the death of 

 an animal, contractions may be excited in any part of the alimentary 

 canal, from the pharynx to the rectum, according to the trunks which 

 are irritated, in the heart, after its ordinary movements have ceased, 

 in the aorta, vena cava, and thoracic duct, in the ductus choledochus, 

 uterus, fallopian tubes, vas deferens, and vesiculse seminales. But the 

 very same contractions may be excited, by irritating the roots of those 

 Spinal nerves, from which the Sympathetic trunks receive their white 

 fibres ; and there is, consequently, strong reason to believe that the 

 motor power of the latter is entirely dependent upon the Cerebro-spinal 

 system. Whatever sensory endowments the Sympathetic trunks pos- 

 sess, are probably to be referred to the same connexion. In the ordi- 

 nary condition of the body, these are not manifested. The parts ex- 

 clusively supplied by Sympathetic trunks do not appear to be in the 

 least degree sensible ; and no sign of pain is given when the Sympa- 

 thetic trunks themselves are irritated. But in certain diseased conditions 

 of those organs, violent pains are felt in them ; and these pains can 

 only be produced through the medium of fibres communicating with the 

 sensorium through the spinal nerves. 



