Another very remarkable result of the sec tion is displayed in the animal's mode of pro gression as related by Magendie: " when the two nerves are cut upon an animal it seems blind, and its mode of progression is most sin gular; it advances only with the chin leant strongly upon the ground, pushing thus its head before it, and using it as a guide as the blind does his staff: the progression of an animal in this state differs altogether from that of an animal simply deprived of sight ; the latter guides itself easily by means of its whiskers, and by the sensibility of the skin of its face ; it stops at hollows, feels obstacles, and, in fine, it would be difficult to know whether it is blind or not ; while the animal whose fifth nerves have been cut has but one mode of moving, and instead of avoiding obstacles, it persists often in pushing against them for several hours, so as finally to exco riate the skin of the anterior part of the head."• This account, which is well calculated to excite at first extreme surprise, is after all strictly consistent, and illustrates strongly the importance of the nerves in question : in fact to the animal so circumstanced the head and face must be as a part which it does not possess, or rather of which it has been suddenly deprived, and which it yet believes itself to retain ; it can have no consciousness of their existence, while from habit, memory, and ignorance of the real condition of the parts, it yet believes them to be present, and to exercise all their usual func tions. Thus the human being whose limb has been removed without any knowledge of what has actually occurred believes that he still pos sesses it, acts as if he did, and is only con vinced of his loss by the evidence of the senses of sight and touch. In like manner the ani mal acts under the impression that it still possesses its ordinary faculties, and being altogether unconscious of the contact of ob stacles in consequence of its loss of sensation in the part which encounters them, it acts as if it were not in contact with them, and endeavours still to advance, while it is unable to make use of sight, if this faculty be retained, as a a guide, because it has lost the correcting and regulating assistance of the sensation of its face as exercised through its whiskers ; and hence it does not appear to the author that the apparent blindness of the animal proves real blindness. Unassisted sight cannot teach us the distance of objects ; and the animal sud denly deprived of the faculty of sensation may see the object, but not being made aware of its contact, must suppose that it has not reached it, inasmuch as the usual notice of its presence is not given by the sensibility of the face.
Lastly, when the nerves have been divided upon both sides, the lower jaw ceases to be supported by its muscles, and falls.* influence if disease on the filnetions of the nerve.—The inferences drawn from the anatomy of the nerve and from physiological experiment conjointly have been confirmed in a remarkable manner by the effect of disease of the nerve upon the functions of the parts to which it is distributed : several instances have been pub lished exemplifying either partially or com pletely that effect, when, whether from disease of the trunk of the nerve itself or from pressure upon it, its office has been interrupted, all the parts supplied by it are deprived altogether of both their tactile and ordinary sensibility: this loss of sensibility extends to the whole of the corresponding side of the head so far as the distribution of the nerve reaches to the fore head, temple, ear, surface of the eye and its appendages, cheek, nostril externally and inter nally, lower part of the face, lips, and mouth, the corresponding half of the tongue, of the palate, and the fauces ; upon all these parts the roughest contact produces no perceptible im pression; inflammation is not attended by pain, the most pungent or irritating effluvia do not affect the nostril or the conjunctiva, and the sense of taste is altogether lost in the ante rior part of the same side of the tongue : at the same time the muscles of mastication—the ex ternal ones at least—lose their contractile power, remain inactive during the process and waste, whence are produced a flattening and depres sion in the site of the temporal and masseter, with prominence of the adjoining points of bone: however the special senses continue un affected apparently, unless in so far as the sense of contact may be necessary to the perfect or ordinary fulfilment of their function, the olfac tory function seems much impaired ; the pa, tient is insensible to the impression of ammo nia, snuff, or other pungent agent, but still ac knowledges a perception of odour. Vision
continues throughout, and appears unaf fected, unless from the supervention of in flammation, by which the eye may be spoiled, or from the extension of the disease to the optic nerve or the brain : in the case before alluded to, which the author has witnessed, vision re mained perfect for a considerable time ; amau rotic symptoms supervened during the course of the disease ; but even after the occurrence of opacity of the cornea in consequence of in flammation, the patient could still distinguish light. Hearing appears to have been affected in most, if not all the cases, in which the dis ease had attained a considerable degree ; it was so in the case seen by the author ; the sense of contact would seem associated with the perfect exercise of the sense. The facial muscles re tain their contractile power ; in the instance alluded to, though the temporal and masseter seemed quite paralyzed, the buccinator acted with energy as ascertained by holding the cheek between the finger and thumb during its con tractions ; the slight want of adjustment, which may occur about the mouth, seems caused by the want of sensation in the lips. Lastly, in all such cases the eye of the affected side is liable to have inflammation excited in it by incidental causes ; for the most part this occurs at an advanced stage of the disease, and can be referred to some exciting cause ; it is attended by but little, if any pain, and opacity of the cornea is an usual result.*