-04 T1IE SENSE OF TOUCH. 



a very delicate and accurate sense of touch, which renders 

 it sensible of the impressions of heat and cold, pain, and 

 mechanical pressure, and consequently of the form of 

 surfaces. The tongue may lose its common sensibility, 

 and still retain the sense of taste, and vice versa. This fact 

 renders it probable that, although the senses of taste and 

 of touch may be exercised by the same papillae supplied 

 by the same nerves, yet the nervous conductors for these 

 two different sensations are distinct, just as the nerves for 

 smell and common sensibility in the nostrils are distinct ; 

 and it is quite conceivable that the same nervous trunk 

 may contain fibres differing essentially in their specific 

 properties. Facts already detailed (p. 547) seem to prove 

 that the lingual branch of the fifth nerve is the seat of 

 sensations of taste in the anterior part of the tongue : and 

 it is also certain, from the marked manifestations of pain 

 to which its division in animals gives rise, that it is like- 

 wise a nerve of common sensibility. The glosso-pharyngeal 

 also seems to contain fibres both of common sensation and 

 of the special sense of taste. 



The concurrence of common and special sensibility in 

 the same part makes it sometimes difficult to determine 

 whether the impression produced by a substance is per- 

 ceived through the ordinary sensitive fibres, or through 

 those of the sense of taste. In many cases, indeed, it is 

 probable that both sets of nerve-fibres are concerned, as 

 when irritating acrid substances are introduced into the 

 mouth. 



The impressions on the mind leading to the perception 

 of taste seem to result, as already said, from certain 

 changes in the internal condition of the nerves produced 

 by the contact of sapid substances with the papillae in 

 which the fibres of these nerves are distributed. This 

 explanation, obscure though it be, may account generally 

 for the sense ; but the variations of taste produced by 

 different substances are as yet inexplicable. In the case 



