312 



FIFTH PAIR OF NERVES. 



also from the orbit, the eye and its appendages, 

 and in our operation for the division of the 

 nerve we do less violence either in their vicinity 

 or actually to them, until the operation is per- 

 formed at such a distance from those parts, 

 that they are not involved in the injury inflicted. 

 Thus the nerve cannot be divided through the 

 temporal fossa without great violence done to 

 the parts in the vicinity of the orbit, and con- 

 nected with the eye as well as the fifth nerve, 

 as is evident from the result, and as has been 

 explained elsewhere.* In the section be- 

 tween the ganglion and the pons, the violence 

 is inflicted at a part more remote than the 

 former, from the orbit, &c., and here, according 

 to his own account, the effect upon the eye 

 was much less considerable. But the most re- 

 markable fact is, that the alterations of nutrition 

 are much less marked than in the former mode 

 of experiment ; there forms only a partial in- 

 flammation at the superior part of the eye, and 

 the opacity which ensues occupies but a small 

 segment upon the circumference of the cornea 

 at the superior part ; and in the third case the 

 parts injured are so far removed from the eye, 

 (in dividing the nerve on the margin of the 

 fourth ventricle, Magendie exposed the parts by 

 " opening the spinal envelopes between the 

 occiput and the first vertebra,") that the effects 

 of the injury could not, under ordinary circum- 

 stances, extend to it, and accordingly in it no 

 alteration occurred. It would seem, then, that 

 the great violencef inflicted, either in the vici- 

 nity of the eye or actually to its appendages, 

 constitutes the primary and immediate cause of 

 the alterations which took place in the eye in 

 the experiments under consideration. But it is 

 likely they were the result of more causes than 

 one, for there were also engaged in the experi- 

 ments other agencies, the influence of which 

 must have enhanced greatly that of the violence 

 inflicted by the operation; thus, in the first 

 place, in some of the instances at least, and 

 we have no evidence that it was not so in all, . 



* It is hardly possible to conceive the section 

 effected at the point and in the mode adopted, 

 without a division of most of the nerves and vessels 

 supplying the eye and its appendages. 



t A better idea of the injury likely to be inflicted 

 in the experiment will be formed from a brief ac- 

 count of the mode of conducting it. A lancet- 

 pointed style is driven into the cranium through 

 the temporal fossa and through its base, and when 

 carried in to such depth as the experience of the 

 operator teaches him to be sufficient, its point is 

 moved upward and downward, until the loss of sensa- 

 tion in the superficial paits assures him that the filth 

 nerve has been divided. After such a proceeding the 

 question should rather be, what mischief has not 

 been done than what has. There cannot be any 

 assurance that, in the division of the fifth, the third, 

 fourth, and sixth nerves with the branches of the 

 sympathetic nay, the optic itself have not been 

 involved : and if to this be added the almost cer- 

 tainty of dividing the internal carotid artery, from 

 which the supply of blood to the internal structures 

 of the eye is directly derived, and the division of 

 which causes the death of the greater number of 

 the subjects of experiment, an amount of injury 

 will be made out, quite adequate to account for the 

 total loss of the eye, and which must reduce the 

 influence of the fifth in producing it to a low degree 

 indeed. 



a highly irritating agent was introduced, and, 

 in consequence of the insensibility of the organ, 

 probably in considerable quantity, into the eye; 

 and in the second the eye was left under cir- 

 cumstances more than enough to excite inflam- 

 mation and to produce serious injury to it, 

 though the organ had remained in full posses- 

 sion of all those safeguards with which its sen- 

 sibility and the sympathetic action established 

 thereby between its several protecting appen- 

 dages naturally endow it ; for " the eye was 

 dry;" and " the eyelids were either widely 

 open and immoveable, or else they were glued 

 together by the puriform matters, which were 

 dried between their margins;" and an organ so 

 circumstanced has abundant cause for inflamma- 

 tion, independently either of nervous influence 

 or of its absence. It may be said that Magen- 

 die has proved that neither the open state of 

 the eyelids nor the want of the lachrymal secre- 

 tion is adequate to the effect. Admitting for a 

 moment that he has, he certainly has not shewn 

 that the combined influence of the two is inad- 

 equate to produce it ; but the first position is 

 by no means satisfactorily established: his 

 mode of determining the question, whether the 

 inflammation was excited by the eye remaining 

 constantly open or not, was by the division of 

 the portio dura, and his experiment has certainly 

 proved that the effect of the section of that 

 nerve will not excite inflammation in the eye, 

 but no more; inasmuch as such section does 

 not produce a permanently open state of the 

 eye : an eye so circumstanced will be closed 

 during sleep, and even during the waking state 

 it requires attention and experience in such 

 observations to discover that the animal has 

 lost the power of closing the lids by a muscular 

 effort of those parts themselves ; for by the sud- 

 den exertion of the power of retracting the eye, 

 which inferior animals possess to a remarkable 

 degree, the lids become nearly, if not quite, 

 closed, and the animal appears to wink as well 

 as before, while by rolling the eye the different 

 parts of its surface are in turn brought beneath 

 the lids, and thus no one part is ever left long 

 absolutely uncovered. So great indeed is the 

 power which brutes possess in this respect, that 

 the author has seen a dog in which the portio 

 dura had been divided on one side, presented 

 for observation, and persons aware that the 

 nerve had been divided, yet not able to disco- 

 ver on which side it had been done, and even 

 deny that the lids were paralyzed on either side, 

 until something was approximated to each eye 

 successively, when the uninjured eye was at 

 once closed, but the other remained open, aiuT 

 the animal appeared looking at the object, 

 which it was unable to exclude. It is obvious, 

 then, that the question has not been and cannot 

 be determined in this way. 



To the causes already enumerated must be 

 added the loss of the nervous influence, for it 

 is not intended, in what has preceded, to assert 

 that the section of the fifth has no share in the 

 production of the changes in the eye, but only 

 that it is not the primary or essential cause of 

 them. Indirectly it must contribute powerfully 

 to produce and aggravate, or it may even excite 



