154 PHYSIOLOGY. 



25. The ganglionic, or great sympathetic nerve, consists in 

 a series or chain of ganglions, extending from the base of 

 the cranium to the extremity of the sacrum. They are 

 placed on the lateral part of the bodies of the vertebrae, and 

 are united to each other by intermediate nervous cords, and 

 send off continually filaments to all the adjacent organs. 

 With the exception of the neck, there is a ganglion for each 

 intervertebral space, both of the true vertebrae and sacrum. 

 Besides these, there are other ganglia situated around the 

 trunks of some of the large vessels of the abdomen^ These 

 ganglia are composed of a mixture of cineritious and medul- 

 lary matter, and are supposed to be the centres of peculiar 

 nervous power. 



26.<JAs to the functions of this order of nerves, there is 

 good reason to believe that the peculiar vitality of every 

 organ in the body directly depends on them. Most physi- 

 ologists believe that they preside over the involuntary func- 

 tions, as secretion, nutrition, absorption, calorification, &c. 

 Others suppose that the office of the ganglions is to render 

 the organs, which are supplied with nerves from them, inde- 

 pendent of the will. As branches from them, accompany 

 the blood-vessels throughout their course, every part of the 

 body must, to a certain extent, be under their influence. 



27. There have been three hypotheses prevalent in respect 

 to the functions of the nerves. The first, that the brain 

 secretes a fine fluid, which circulates through the nerves, 

 called animal spirits, and which is the medium of communi- 

 cation between the different parts of the nervous system ; 

 the second regards the nerves as cords, which transmit all 

 impressions by a kind of vibration ; and the third ascribes 

 nervous influence to electricity or galvanism. But there 

 is no proof whatever of the existence of any such fluid ; 

 the doctrine of vibrations is pretty much abandoned ; while 

 the. electrical hypothesis, though at first view perhaps 

 more plausible, has probably no better foundation to rest 

 upon. 



