CHAP. XI.] FUNCTIONS OF NERVES, HOW DETERMINED. 305 



stances. It had already been ascertained by Lehot, Bellinger!, 

 Nobili, and Marianini, that compound nerves, the sciatic for in- 

 stance, are at first excited equally on closing and on opening the 

 electric circuit, whether the current be direct (. e. from the brain 

 or cord to the nerves), or inverse (from the nerves to the brain or 

 cord) ; but after a time they are excitable, as shewn by the contrac- 

 tion of the muscles below the point of the nerve stimulated, only on 

 closing the direct current or opening the inverse. With a purely 

 motor nerve, however, such as the anterior root of a spinal nerve, a 

 different result is obtained ; inasmuch as the contractions of the 

 muscles can only be excited on opening the direct current or closing 

 the inverse.* 



Sometimes we find that, if the trunk of a nerve be divided at some 

 distance from its origin, irritation of the central segment will excite 

 contractions, whilst that of the peripher alone will fail to do so. 

 Such a nerve has been called an excitor ; for it causes muscular 

 movement, not by its direct influence upon muscles, but by excit- 

 ing the centre, which in its turn stimulates motor nerves arising 

 from it. We judge a nerve to be sensitive, if, when irritated in 

 man or the lower animals during life, a peculiar sensation or pain 

 be excited ; or if section of it destroys the sensibility of the parts 

 to which it is distributed. 



Fourthly. Clinical observation furnishes most valuable opportuni- 

 ties of testing the true function of nerves. We observe a particular 

 form of paralysis, and we inquire what nerve is diseased ; we 

 find pain felt in particular regions, and we ascertain that this is in 

 consequence of a morbid state of particular nerves ; certain func- 

 tions are impaired or suspended, if certain nerves be affected with 

 disease. A woman, lately in King's College Hospital, had a sin- 

 gular train of symptoms, which were at first referred to hysteria. 

 However, in a little time they became so confirmed, that no 

 doubt could be entertained of organic lesion. There were ptosis 

 of the upper lids, paralysis of the muscles of the eyeball sup- 

 plied by the third nerve, paralysis of the pharynx, so that the 

 power of deglutition was destroyed, paralysis of the trapezii 

 muscles, and of those on the back of the neck, a great feeble- 

 ness of voice. She died like one asphyxiated. After death, the 

 following nerves were found involved in a thickened neurilemma, 

 with altered nerve tubes, the third pair, the fourth pair on the left 

 side, the glossopharyngeal, the vagus, the spinal accessory ; each of 



* Matteucci et Longet, sur la relation qui existe entro le sens clu courant 

 61ectrique et les contractions musculaires dues k ce courant. Paris, 1844. 



VOL. T. X 



