On turning to the pathological evidence which bears upon this question, we find an apparent contradiction in the phenomena re corded by different observers; but this is in a great degree removed by a more careful ex amination; and the evidence on the whole preponderates in favour of the preceding con clusions. We shall make use of the excellent summary recently put forth by Dr. J. Reid*: —" In the single cases observed and recorded by Mayo, Serres, Romberg, Mr. Bishop, and Todd and Bowman, and in the two cases by Mr. Dixon, both common sensation and the sense of taste were annihilated in those parts of the tongue supplied by the fifth pair ; while in one case related by Mr. Noble, and ano ther by Vogt, common sensation was lost in the parts of the tongue supplied by the third branch of the fifth pair, yet the sense of taste remained in these parts ; and in a second case related by Air. Noble, there was loss of taste with maintenance of feeling." In some of these cases the loss of the sense of taste ap peared to extend to the base of the tongue ; but there was evidence that in these the glosso-pharyngeal nerve was also involved in the paralysis. " We have no proof," con tinues Dr. Reid, "that in the cases related by Mr. Noble and Vogt, the whole of the fila ments of the fifth pair sent to the tongue were affected ; and in the case of Vogt the derangement of the nerve was only tempo rary, for the patient recovered the sensation of the part paralysed after the end of six weeks. We believe that these cases, when examined more closely, will rather be regard ed as affording arguments in favour of the opinion, that the same nervous filaments do not convey inwards the impressions which excite pain and touch and the impressions which excite taste ; and that different fila ments for conveying inwards the impressions that excite these sensations are bound up in the lingual branch of the fifth pair." There is believed to be no case on record, in which the whole of the fifth pair, or of the third branch of it, was found to be diseased after death, and in which, during life, the sense of taste had been retained in the anterior and middle parts of the tongue. The evidence of pathology, therefore, is in favour of that con clusion, as to the participation of the fifth pair with the glosso-pharyngeal in the sense of taste, at which we had arrived on other grounds.
The question still remains, however, as to the speciality of the nervous fibres which con vey the gustative impressions ; that is, whether they are the common sensory fibres, whose peculiarity of function depends on the nature of the papillary apparatus at their peripheral origin ; or whether they are incapable, like the fibres of the olfactive, optic, and auditory nerves, of conveying impressions of the ordi nary sensorial kind, being adapted exclusively to receive and transmit the peculiar impres sions made by sapid bodies. Now, in favour of the first view, it may be urged, that the conditions of the sense of taste are so nearly allied to those required for the exercise of touch, that the two can scarcely be dis tinguished on this ground, and that the fifth pair and the glosso-pharyngeal are both nerves of common as well as of gustative sensibility ; neither of which can be affirmed in regard to the three other senses, or of the nerves which minister to them. But, on the other hand, it
must be remarked, that these nerves do not seem to be endowed with gustative and com mon sensibility in equal proportions ; for the glosso•pharyngeal, which is decidedly more susceptible than the lingual to gustative im pressions, far less readily excites manifesta tions of pain when subjected to mechanical irritation. Hence, it would seem not im probable, that there may be in each a mixture of the fibres which minister to the sense of taste with those of tactile sensibility ; and that the former may be so far special in their endowments, as to be capable of receiving only the peculiar impressions made by sapid bodies, to which the latter may be insensible. Such a view would seem to be supported by the cases of Vogt and Noble just referred to ; and it is in harmony with the views to which we are led from the consideration of the diversities manifested between the sense of heat and cold and that of simple contact. [See To u cu.] Gustative Papillcc.—The tongue is copiously furnished with a papillary structure, bearing a close resemblance to that of the skin, but in many respects more complicated. Re ferring to the article TONGUE for a more par ticular anatomical description of these papilla, we have now to inquire into their connexion with the sense of taste. According to the recent investigations of Messrs. Todd and Bowman, the lingual papillm are either simple or compound ; the former, which do not differ from those of the cutaneous surface in any other obvious character than the nature of their epithelial investment, are scattered over the whole surface of the tongue, in parts where the others do not exist, but they also par ticipate in the formation of the compound papillm ; the latter are of three kinds, the cir cumvallate or calyciform, the fitngiform, and the circumvallate papillae, are only eight or ten in number, and are restricted to a small space at the base of the tongue, consist merely of groups of simple papilla, arranged in a peculiar manner, and separated from those of the adjacent mucous membrane by a circular fissure. Into these simple papillm it has not yet been found possible to trace any distinct nerve-fibres, though there can be little doubt that it is penetrated by at least the essential part of them.—The fungifornz papillm are scattered singly over the surface, chiefly about the sides and apex, and but very sparingly in the middle of the dorsal region, though they are abundant in front of the cir cumvallate papilla. These are composed of aggregations of simple papillae, which rise, however, considerably above the surface, and are covered with an epithelium so thin that they are distinguished by their blood-red colour. Fasciculi of nerve-tubes may be dis tinctly traced into them ; but of the nature of their termination it would be unwise to give a positive statement. Some of the ap pearances presented by them favour the idea that they form loops at their peripheral ex tremities ; whilst, in other instances, the tu bular portion of the fibre, with the white substance of Schwann, seems to terminate somewhat abruptly, whilst the central axis is continued onwards into the substance of the enveloping t;ssue, in which it loses itself.