FIFTH PAIR OF NERVES. 



305 



could not be entertained : the fifth nerve had 

 also been fairly divided : thus far, therefore, 

 his conjecture was disproved. Pursuing his 

 inquiry still further, he found in his next 

 experiment that no indication whatever of pain 

 was manifested by the animal on irritation of 

 the facial on the side on which the fifth nerve 

 had been cut ; but in two succeeding experi- 

 ments he ascertained that while irritation of the 

 nerve anterior to the meatus auditorius pro- 

 duced no other effect but spasms of the nasal 

 and labial muscles, when exerted posterior to 

 that point it excited manifest evidence of suf- 

 fering : this latter circumstance he accounts for 

 by the communications of the posterior part of 

 the facial with other sentient nerves besides the 

 fifth, and he has come to the conclusion that the 

 former nerve is not endowed with independent 

 sensibility, but that it derives the property from 

 the fifth and other sentient nerves : this ques- 

 tion, however, requires further investigation.* 



Relation of the fy'th pair of nerves to the 

 special senses. The organs of the special senses 

 are in the higher classes and in the case of 

 smell, sight, and hearing, each supplied with 

 nerves from at least two sources. Besides the 

 particular nerves, which are generally consi- 

 dered to be the source or medium of the spe- 

 cial sense, they are furnished with branches 

 from the fifth pair; and a question must, at the 

 outset, be asked in regard to the two nerves 

 derived from these different sources, as to 

 which is to be considered the proper nerve of 

 the peculiar sense enjoyed? In connexion 

 with the two separate nervous supplies, it is 

 also to be observed that each organ enjoys two 

 kinds of sensibility, viz. the special sensibility, 

 through which sensations of the particular sense 

 are received, and the general sensibility, in 

 which the several organs of the body partici- 

 pate, and which is the medium through which 

 impressions of contact are conveyed. The exis- 

 tence of the special sense, the coincidence of 

 the particular nerve, the impairment or loss 

 of the special function uniformly consequent 

 upon the injury or destruction, whether by 

 disease or otherwise, of that nerve ; and the 

 community bo^i of function and distribution, 

 displayed by the nerve from which the organs 

 of the senses are in common supplied, have 

 led physiologists generally to the conclusion 

 that in each case the particular nerve is the 

 medium of the special sense, and that the 

 fifth nerve confers upon the organs of the spe- 

 cial senses general sensibility only. The con- 

 clusion thus commonly adopted has been at 

 different times called in question : thus Mery 

 and Brunet, in 1697, denied to the nerves of 

 the first pair the function of smell, and attri- 



* Eschricht, de functionibus nervorum facici et 

 olfactus organi, Hafn. 1825, [The superficial tem- 

 poral nerve doubtless contributes mainly to supply 

 sensibility to the posterior twigs of the facial : but 

 so much difficulty do some see in satisfactorily 

 accounting for the sensibility of the portio dura, 

 that they find it convenient to discover two roots of 

 origin, and a ganglion on one, thus reducing it to 

 the class of compound nerves. See Arnold, Icones 

 capitis nervorum ; also Gaedechens, nervi facialis 

 physiologia et pathologia. ED.] 

 VOL. II. 



buted this sense to the fifth nerve.* The ques- 

 tion of the connexion between the fifth nerve 

 and the special senses is one of much difficulty, 

 and probably we are not as yet in possession of 

 sufficient data from which to draw a positive 

 conclusion upon it when viewed in all its bear- 

 ings. It resolves itself into three: 1. how far 

 the nerve may be concerned in the perception 

 of special sensations in those cases in which 

 nerves, considered to be specially intended for 

 their perception, exist: 2. how far its co- 

 operation or influence may be necessary to 

 enable the special nerves to fulfil their func- 

 tions: 3. how far it may be capable of taking 

 the place of those special nerves, and of be- 

 coming, under certain conditions, media of 

 perception to sensations, for which, in other 

 cases, peculiar nerves are conferred. We shall 

 review the relation of the nerve to the several 

 senses in succession, bearing in mind the three 

 points to which our attention is to be directed. 

 That it is a medium of perception in the case 

 of two senses, viz. touch and taste, is already 

 so universally acknowledged that it is unneces- 

 sary to dwell upon the point. 



The importance of the fifth nerve in the 

 three other senses of smell, sight, and hearing, 

 has been advocated by several physiologists, 

 and more particularly by Magendie, who ap- 

 pears disposed to view the fifth nerve as the 

 source or medium of all the three. His appli- 

 cation of this doctrine, however, has reference 

 more particularly to the sense of smelling, 

 upon which he has performed a series of expe- 

 riments, of which the following is a summary : 

 he destroyed entirely the olfactory nerves within 

 the cranium, and he found the animal still 

 sensible to strong odours, such as ammonia, 

 acetic acid, essential oil of lavender. The sen- 

 sibility of the interior of the nasal cavity had 

 lost nothing of its energy ; the introduction of 

 a stylet had the same effect as upon a dog 

 which had not been touched. This experiment 

 he performed several times, and always with 

 the same results. He next divided the fifth 

 nerves within the cranium, of course before 

 they had given branches to the nostrils, 

 and found all trace of the action of strong 

 odours to disappear. He hence concluded that 

 smell, in so far as pungent smells are con- 

 cerned, is exercised by the branches of the 

 fifth pair, and that the first is not concerned in 

 the function. To this conclusion he himself 

 starts the objection that the agents used are not 

 odours, properly speaking, but chemical, pun- 

 gent, irritating vapours, and that by the section 

 of the fifth we destroy not the sense of smell, 

 but only the sensibility of the membrane of the 

 nose to these irritating vapours, and he admits 

 the force of the objection with respect to some 

 of the vapours alluded to ; but he denies that 

 it will apply to the oil of lavender or that of 

 Dippel, the effect of which in the experiments 

 is the same. In order to remove the difficulty 

 he destroyed the olfactory nerves of a dog of 

 particularly fine nose, and then enclosing por- 

 tions of food of various kinds in paper, he 



* See Journal Complementaire, v. 20. 

 x 



