Let us next inquire bow far it bears out the opinion that the fifth nerve possesses a proper and direct influence upon the nutrition of the eye : here we shall find ourselves equally at fault for the resemblance which it has been sought to establish. In Magendie's experi ments the section of the nerve preceded the occurrence of the phenomena, and it is reason able to expect, that, here, the loss of sensibi lity, which we are to regard as the analogue of the section, should have preceded the oc currence of the inflammation of the eye ; but no. The patient had a chronic ophthalmia, con sidered scrofulous at the time of his admission; (he was admitted in September, and in De cember he was attacked by acute ophthalmia, attended by edema of the lids; a circumstance not noticed in any of Magendie's experiments;) the inflammation was dispersed, and in the course of January, and not till then, (i. e. four months after his admission and about one after the occurrence of the second inflammation,) the insensibility of the eye was for the first time observed. Surely we have no reasonable grounds here for attributing the inflammation of the eye and the opacity of the cornea to the disease of the nerve, or for supposing that there existed ally connexion, in the relation of cause and effect, between them. If we seek for a resemblance in other points, we shall be equally disappointed. It has been already remarked that oedema of the eyelids, which occurred in this case, is not one of the phenomena of Magendie's experiments. Again, the affection of the gums related is altogether unlike : in Serres' case they are stated to have become inflamed, and to have been affected on both sides, only more on the right than on the left; in Magendie's it is simply stated that they separated from the teeth and only on the side on which the nerve had been divided ; and, lastly, the continuance of sensibility upon the right side of the face throughout casts an im pervious obscurity over the entire.
Besides those effects of the section of the trunk of the nerve which have been discus sed, there are others, for which we are in debted also to Magendie, and which deserve notice.
Ile found after the section of the nerve that the eye was dry, and the motion of winking had ceased ; the globe of the eye itself seemed to have lost all its motions ; the iris was strongly contracted and immoveable. The loss of sensibility in the conjunctiva, and the sus pension of the secretion of the tears, he refers to the loss of the influence of the fifth nerve upon the former part and upon the lachrymal gland : the explanation of the first is in accor dance with the previously established proper ties of the nerve as already ascertained by Mayo, but it is not equally so that the secretion of the lachrymal gland is directly controlled by the same influence, and it remains to be deter mined whether the effect in this case was not an indirect one, consequent upon the previous insensibility of the conjunctiva. The other re sults of the section—the immobility of the eyelids, that of the eye, and the permanent contraction of the pupil—he has not satisfac torily explained : the immobility of the lids may, it appears to the author, be attributed with much probability to the insensibility of the conjunctiva or of the internal structures of the eye, and seems a likely consequence there of: the ordinary action of winking would seem to be called into play through the sensations of those structures, and the cessation of that action upon the loss of their sensibility is as natural ad effect as the immobility of the lips on the contact of food consequent upon the division of the infra-orbital and inferior maxil lary nerves : and this view derives confirmation from the circumstance that in the instance under consideration the immobility of the lids is not the consequence of paralysis, for on the sudden admission of solar light into the eye, the action of the muscle was excited, and the eyelids were closed. The immobility of the
eye itself the author cannot but regard as an incidental circumstance, caused by the com plication to which Magendie himself refers, viz. the division of the motor nerves of the eye along with the fifth, and this explanation is rendered more likely, if not confirmed, by the effect of the section when made between the ganglion and the brain, in which case the motor nerves are not involved, nor the motion of the eye affected. I t is to be regretted that Magendie has not given a report of a dissec tion after death of some of the animals upon which the former experiment had been per formed, by which the question might have been determined. The permanent contraction of the iris is an extraordinary and as yet unex plained effect: it occurred only when the experiment was made upon rabbits, and is at variance with the results of similar experi ments upon other animals, performed both by Mayo and by Magendic himself. In Mayo'se experiments, which were done upon pigeons, in no instance was contraction of the pupil caused by division of the nerves connected with the eye or its appendages. When the optic nerve was divided, the pupil became fully dilated. When the third nerve was divided, the same result ensued ; and when the fifth was divided, the iris contracted as usual on the admission of light; in Magendie's experiments again upon cats and dogs the pupil was en larged:I- The fact is, however, confirmed by Mayo, who found that when the fifth nerve was compressed in a rabbit after death, the pupil became contracted slowly and gradually, and then slowly dilated ; and when the nerve was divided, the pupil became contracted to the utmost, and remained so. A correspond ing difference between the conditions of the pupil after death in the subjects of experi ment has been observed by Mayo, according to whom in the pigeon and cat it is naturally dilated, but in the rabbit, on the contrary, contracted.I It has been already stated that Magendie divided the nerve within the cranium both after and before the occurrence of the ganglion : in the latter case—when the section is made between the ganglion and the brain—the re sults are different in some remarkable respects from those attending the section in the former: the effect upon the senses is equally marked ; but the motions of the globe of the eye are preserved almost always, from which the authnr would infer that the loss of those motions in the former must have been caused by the divi sion of the motor nerves along with the fifth, by the side of the cavernous sinus ; and also the changes which occur in the tissues of the eye are much less considerable ; the inflamma tion and opacity ensue, but not to the same extent.