858 



TASTE. 



On the other hand, as Wagner has truly re- 

 marked, if the surface of the tongue near the 

 root be touched with a clean dry glass rod, or 

 a drop of distilled water be placed upon it, a 

 slightly bitterish sensation is produced ; and 

 this, if the pressure be continued, passes into 

 that of nausea, and if the pressure be increased 

 even excites vomiting. The feeling of nausea 

 may be excited by mechanical irritation of 

 any part of the surface of the fauces and soft 

 palate ; and this feeling is certainly much 

 more allied to that of taste than to that of 

 touch. Further, it has been observed by 

 Henle, that if a small current of air be di- 

 rected upon the tongue, it gives rise to a cool 

 saline taste like that of saltpetre. Thus 

 we find that the peculiar effects of sapid 

 substances upon the nerves of taste may be 

 imitated to a certain extent by other agencies ; 

 and it also appears that the sensations excited 

 by these vary according to the part of the 

 gustative surface on which they operate ; me- 

 chanical or electrical stimulation of the front 

 of the tongue giving rise to a kind of saline 

 taste, whilst mechanical stimulation applied 

 to the back of the tongue and fauces excites 

 the feelings of bitterness and nausea. 



One of the conditions requisite for the due 

 exercise of the gustative sense, is a tempera- 

 ture not departing far on either side from 

 that which is natural to the body. It appears 

 from the recent experiments of Prof. E. H. 

 Weber *, that if the tongue be kept immersed 

 for nearly a minute in water of about 125, 

 the taste of sugar brought in contact with it, 

 either in powder or solution, is no longer 

 perceived ; the sense of touch, usually so 

 delicate at the t'"p of the tongue, being also 

 rendered imperfect. A" similar imperfection 

 of taste and touch was produced by immers- 

 ing the tongue for the same length of time in 

 a mixture of water and broken ice. 



Nerves of Tasle. Much controversy has 

 taken place upon the question whether or not 

 there be a special nerve of taste ; and whether 

 the lingual branch of the fifth pair, or the 

 glosso-pharyngeal, possesses the best claim to 

 this title. The principal points of this con- 

 troversy have been already noticed [See 

 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 glosso-pharyn- 

 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. Broughtonf, 

 have been since, to a certain extent, sup- 

 ported by the experiments of Valentin and 

 Bruns.$ The grounds on which this doc- 

 trine rests are briefly as follows: After re- 



* Mullet's Archiv. 1847,. S. 342. 



f Sixth Report of British Association j p. 125 of 

 Transactions of Sections. 



J De Functionibus Nervorum Cerebralium, &c., 

 1849, p. 41. 



De Nervis Cetaceorum, Tub. 1836 ; quoted by 

 Miiller. 



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 *, with whom Miiller and Gurlt 

 were associated, by Dr. Alcock-f-, by Dr. 

 John ReidJ, by Guyot and Cazalis , by 

 Magendie||, by LongetH, 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 colocynth, 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. 



* De Functionibus Nervorum Linguae Experi- 

 merita. Berol. 1836. 



f Dublin Journal of Medical and Chemical Science, 

 1836. 



1 Edinb. Med. and Surg. Journal, Jan. 1838. 



Archives Generates de Medecine, 1839. 



|| Lemons sur les Fonctions du Systeme Nerveux* 

 1839, torn. ii. 



^f Anatomic et Physiologic du Systeme Nerveux,., 

 1842, torn. ii. p. 225. 



** Articles Nervenphyslologie and Schmecken in 

 Wagner's Handworterbuch der Physiologie. 



