310 



FIFTH PAIR OF NERVES. 



otherwise than by allowing it to come or return 

 to a state from which it is preserved by the 

 presence of the influence ; and there is no 

 good reason, either theoretical or experimental, 

 for believing that the state induced in the 

 case under consideration is one in which the 

 eye would necessarily be, which, in fact, 

 would be natural to the organ but for the 

 restraining influence exerted through the fifth 

 nerve. 



It is easy to imagine that the absence of 

 such an influence should render a part slow to 

 take on any vital action ; though even this, 

 until proved, is an assumption an assumption 

 which we are induced to adopt from the fre- 

 quency witli which sensation and pain are 

 found associated with the establishment of cer- 

 tain vital processes, more particularly inflam- 

 mation, but which is, on the other hand, con- 

 tradicted by the readiness with which inflam- 

 mation and its consequences are excited in 

 parts whose nervous faculties are impaired or 

 destroyed by agencies which make little or no 

 impression when those faculties are retained, 

 and which must be demonstrated before admit- 

 ted, since it is manifest from the occurrence of 

 that process after the destruction of all trans- 

 mitted influence at least, that the principle 

 the main-spring of it must reside elsewhere; 

 and hence that, if in the natural state the nerve 

 influence the process at all by means of such a 

 property, it can be only in the character of a 

 secondary and controlling power. It does, 

 however, seem proved by the result of Magen- 

 die's experiment, that the interruption of the 

 influence did retard the inflammatory process, 

 inasmuch as the eye, on the side of the undi- 

 vided nerve, was very actively inflamed the day 

 after the application of ammonia to it, whilst 

 the other eye did not present any trace of in- 

 flammation ; a circumstance by the way diffi- 

 cult, if not impossible, to reconcile with the 

 doctrine that the process of inflammation is 

 directly influenced in either way, whether posi- 

 tively or negatively, by the power of the nerve ; 

 and further, that the division of the nerve 

 should diminish the vital powers of the eye, 

 and thereby render it less able to resist the 

 effects which inflammatory action tends to pro- 

 duce. But indeed there does not appear any 

 reason for admitting that the alterations which 

 took place in the condition of the eye were 

 produced directly by the loss of nervous influ- 

 ence. Having, as he conceived, disproved, by 

 the experiment related, the idea that the alte- 

 rations were owing to the continued exposure 

 of tlie eye to the air, or to the want of the 

 lachrymal secretion, the only other causes 

 which appear to have occurred to him, Ma- 

 gendie arrived at a conclusion the opposite of 

 that just mentioned, and adopted the opinion 

 that the phenomena " depend upon an influ- 

 ence purely nervous"* exerted by the fifth nerve 

 upon the eye, " an influence independent of 

 the connection of the nerve with the spinal mar- 

 row," ) an influence " proper to the nerve, 



* Anatomic des Systemes neivcux, &c. t. ii. 

 p. 71fi. 



t Journal dc Physiologic, p. 304. 



which has not its source in the cerebro-spinal 

 system, and which is even the more energetic, 

 the farther we remove from that system to a 

 certain distance," of which the following is his 

 proof. " Alterations of nutrition in the eye are 

 the less complete, the less rapid, as we remove 

 farther from the point of branching of the nerves 

 of the fifth pair, and as we cut, within the cra- 

 nium, the fasciculus of origin the nearer to its 

 insertion ; finally, the section of the nerve on 

 the margin of the fourth ventricle no longer 

 produces any alteration in the state of the 

 eye." * In this view there are plainly two posi- 

 tions advanced, viz. that the nerve does itself 

 exert a proper and independent influence upon 

 the nutrition of the eye, and that it is the sec- 

 tion of the nerve which causes the exercise of 

 that influence, or, to use his own words, which 

 is the cause of the inflammation, &c. That 

 the occurrence of the alterations in the eye, in 

 the case in question, is not due to an influence 

 exerted by the brain through the nerve, and 

 that it must proceed from another cause, and 

 that not dependent upon the connection be- 

 tween them, is manifest, since it is consequent 

 upon the interruption of that connection ; and 

 therefore, if the nerve do possess the supposed 

 influence, it must be a proper and independent 

 one: but are we, therefore, to infer that the nerve 

 does exert such an influence upon the organ ? 

 It appears to the writer that we cannot : for can 

 we suppose that the nerve is endowed with a 

 property to be displayed expressly under cir- 

 cumstances, which it is fair to say were not 

 contemplated in the establishment of natural 

 laws, viz. in cases of mutilation? or is it possi- 

 ble that a separate influence can exist in the 

 nerve and increase in energy in proportion as 

 the nerve is curtailed ; for the nearer the section 

 is made to the eye, the more remarkable are 

 the effects; or if any other proof that the nerve 

 does not possess such an influence be wanting, 

 can we suppose that it is possessed for the eye 

 and not for the other parts to which the branches 

 of the nerve are distributed ? Why does not 

 inflammation forthwith assail the nostrils, the 

 mouth, and cheeks upon the mere section of 

 the nerve,f as well as the eye ? Manifestly be- 



* Op. cit. ibid. 



t It is stated by Professor Alison, Outlines of 

 Physiology, p. 147, that inflammation, ulceration, 

 and sloughing are produced sometimes on the mem- 

 brane of the nose and on the gums by section of the 

 fifth nerve, " as was first ascertained by Magendie." 

 The only passages approaching at all to this state- 

 ment, which the author has found in Magcndie'a 

 writings, are at page 181, Journal de Physiologic, 

 t. iv, and page 717, Anatomic des Systemes Ner- 

 veux, &c. JDesmotilins et Magendie, t. ii. In the 

 first he says, " when a single nerve is cut, there 

 appear alterations in the nostrils, the mouth, the 

 surface of the tongue on that side ; the half of the 

 tongue becomes whitish, its epidermis is thickened, 

 the gums quit the teeth ; the alimentary matters 

 sink into the intervals which are formed ; probably 

 because the animals having no longer their atten- 

 tion attracted by the sensation of the tendency of 

 the matters to pass between the teeth and the 

 gums, push them thither without perceiving it;" 

 and in the second, " a part of the broken food re- 

 mains on that side, between the teeth ami the 

 check, and its contact terminates by ulcerating the 



