FIFTH PAIR and GLOSSO-PHARYNGEAL] ; a short review of it, however, with a notice of the most recent inquiries on the subject, will be here desirable. That the geal is the special nerve of taste, and that its complete section on both sides destroys the sensibility to gustative impressions, was first affirmed by Panizza ; and his conclusions, adopted by Dr. M. Hall and Mr. Broughton have been since, to a certain extent, sup ported by the experiments of Valentin t and Bruns. The grounds on which this doc trine rests are briefly as follows :.—After re covering from the depression which is the immediate consequence of the operation, a dog whose glosso-pharyngeal nerves have been divided is said to eat pieces of meat rendered bitter with colocynth, and to drink milk and water dosed with the same drug, without any repugnance ; whereas if the lingual nerves be divided and the glosso-pharyngeals left entire, the bitter morsel is rejected as soon as it reaches the back of the mouth, although it may have been at first seized very hastily. But, on the contrary, it has been affirmed by Kornfeld TM, with whom Muller and Gurlt were associated, by Dr. Alcock -I-, by Dr. John Reid 1, by Guyot and Cazalis §, by Magendiejl, by Longetlf, and by Volkmann and Bidder**, that distinct indications may be obtained of the persistence of the sense of taste, after complete section of the glosso pharyngeal nerves on both sides. Of a dog in which the nerve had been divided before giving off' a single filament, Dr. J. Reid states : —" I have repeatedly fed that dog with morsels of animal food from my hand ; and after he had taken several morsels in this way, which he readily swallowed, I then pre sented a morsel similar in size to the others, and with the coloeynth, concealed in a way that he could not see it ; but no sooner was it taken into the mouth than it was rejected with evident symptoms of disgust. This was repeated more than once." Bidder found that although two dogs whose glosso-pharyn gei had been divided, swallowed pieces of flesh soaked in an infusion of colocynth, which another dog whose nerves were uninjured at once rejected, yet certain movements of the lips and tongue were observed, which showed that these were not altogether relished. It is obvious that, in such an inquiry, positive evidence of the continuance of the sense of taste is more conclusive than the negative evidence from which its absence may be in ferred. It is right to bear in mind that, as Wagner has pointed out, dogs when they are hungry will devour meat however strongly seasoned with bitter drugs, though all their nerves be entire. Dr. Reid makes the re mark, in explanation of the results of Panizza, that one of the dogs on which he had divided the glosso-pharyngeal nerves, would eat the morsel of meat containing colocynth, rather than lose it, when very hungry ; though he refused it, if he saw any prospect of procuring another free from the bitter. Wherever any
such evidence of the persistence of the sense of taste was obtained, this appeared specially to exist in the anterior portion of the mouth.
On the other hand, it has been maintained by some physiologists (especially Magendie, Muller, Gurlt, and Kornfeld), that the lin gual branch of the fifth pair is the special nerve of taste ; although Aliiller does not altogether exclude the participation of the glosso-pha ryngeal as having a share in the transmission of gustative impressions from the posterior part of the tongue and the fauces. The ex periments of Dr. Alcock and others, however, appear to show that very distinct indications of gustative sensibility are presented by ani mals in which this nerve has been divided, the sense being merely deficient in the anterior part of the tongue.
On the whole, then, it may be concluded from experiment, that the glosso-pharyngeal nerve and the lingual branch of the fifth pair minister alike to the sense of taste ; the for mer being concerned in the transmission of gustative impressions from the fauces and the posterior part of the tongue, and the latter from the anterior portion of the tongue ; and the former being the special recipient of the impressions which produce the sense of nau sea. This inference is so completely in har mony with the results of anatomical inquiry, that it may be considered as having a very strong claim to reception as a physiological truth. The branches of the glosso-pharyn geal appear to constitute the sole nervous supply of that region at the base of the tongue, of which the circumvallate papillm form the centre, and also of the sides of the tongue near the base. As it is universally admitted that these parts are acutely endowed with gustative sensibility, we cannot help re garding the glosso-pharyngeal nerve as its instrument. On the other hand, the middle and anterior parts of the dorsum of the tongue appear to be solely supplied from the fifth pair, —the tip, however, receiving a branch from the glosso-pharyngeal, which runs towards it, along the under surface. It has been denied by some physiologists that the central por tion of the upper surface possesses the proper gustative sensibility ; but we fully coincide in the statements of those who maintain the affirmative : and although it must be admitted that the sense is not so acute as it is at the base, sides, and apex of the tongue ; yet this may be fairly attributed to the greater thick ness of the epithelial investment, and to the predominance of the conical papilla; over the fungiform in the central region.