But was the inflammation caused by the section of the nerve? This question, which cer tainly ought to have been determined satisfac torily before a theory had been founded upon the assumption, appears to the writer to have been decided too hastily in the affirmative. If the section were the cause, no sufficient reason can be assigned why it should occasion inflam mation in one part, to which the nerve is distri buted, and not in another, yet such is the case; the eye is the only part in which inflammation supervenes, either so uniformly or so quickly as to afford any ground for attributing the pro cess to the section. In the second place, were the section the real and essential cause, it can not be supposed either on the one hand that non-essential circumstances could influence, or at all events prevent the effect, or on the other, that they could produce it. Now it will pre sently appear that both the one and the other may take place; and a comparison of Magen die's experiments and their results would alone suffice to skew that the real cause is to be sought elsewhere than in the section of the nerve. Magendie divided the nerve in three different situations ; first, through the temporal fossa ; secondly, within the cranium, between the Gasserian ganglion and the pons Varolii ; and thirdly, at the margin of the fourth ventri cle ; and his own general account of the results, which has been already cited, is as follows : " those alterations in the nutrition of the eye are the less complete, the less rapid, as we recede more from the point of branching of the nerves of the fifth pair, and as we cut, within the cra nium, its fasciculus of origin the nearer to its insertion ; finally, the section on the margin of the fourth ventricle no longer produces any alteration." It is plain, then, that the nerve may be cut, and the changes in the eye ensue or not, according to circumstances to be yet explained. On the other hand, that effects similar in kind, if not equal in degree, may be produced by circumstances not essential to their production,—according to the doctrine main tained, but incidentally associated with the supposed cause,—that such effects may be pro duced by such circumstances, when dissociated from the other and operating separately, the author feels justified in asserting, from the re sult of some experiments lately made by him self, which lead to the conclusion that similar effects may be produced without the section of the nerve at all, and that an injury in the vici nity of the orbit may excite theta though nei ther the trunk of the fifth itself, nor its ophthal mic division have been divided. In an endea vour to determine the nerves of taste, he under took the removal of the ganglion of Meckel from the dog; in order to accomplish this it was necessary to displace the zygoma and the coro noid process of the jaw; he attempted it seve ral times before he succeeded, and failed at different stages of the operation ; but in almost every instance the eye of the same side became bleared within the next two days. The animal kept it nearly closed: a whitish puriform mat ter was discharged from it, in quantity propor tioned to the case, which concreted between the lids ; and the animal made no attempt to remove the matter or cleanse the eye: the affec tion of the eye was always proportioned to the violence done, and abated with the inflamma tion of the wound ; and in one of the instances in which the ganglion was removed, it actually produced opacity of the cornea, and ulceration in that structure, which continued after the lapse of more than a month from the operation ; yet most assuredly neither infra-orbital nor ophthalmic nerves had been divided. Thus, if, on the one hand, the nerve may be cut and the changes not ensue, on the other it may be left uncut, and the changes may occur.
It may be objected that the effects here de scribed fall very far short of those which took place in the experiments of Magendie. That they fall short of those which occurred on the division of the nerve in the temporal fosgt is quite true, but it is equally so that they far ex ceed those consequent upon the section at the margin of the fourth ventricle. The objection, therefore, would be devoid of weight, and if we suppose superadded to the violence already done when the nerves are not divided, the ad-; ditional violence necessarily inflicted in the division of them, we shall have a ready expla nation furnished of the higher degree to which the effects produced amount in one case than in the other.
From the preceding considerations it appears to the author necessary to infer, that the changes which supervene in the eye after the section of the fifth nerve in certain cases, take place inde pendently of the section, as the primary, imme diate, or proper cause; for were it otherwise, it cannot be supposed either that the difference of half an inch to. one side or the other, as re gards the point of section, could so influence the cause as to prevent or allow these changes, or that they could occur, even in degree, without it.
IIow, then, are the phenomena to be ex plained? It has been said by Magendie that they are less marked the more we recede from the point of branching of the nerve ; but it is to be further observed, that, as we recede from the point of branching of the nerve, we recede 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 ease 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 violence-f 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,— 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, and 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.