718 Dr Graves on the Sense of Touch 



in structure, in function, or in the use habitually made of them, 

 and the legs will appear to be more clearly and distinctly felt 

 than when they are applied to one and the same surface, even 

 though it be the more sensitive of the two ; thus the legs, when 

 in contact, one with the inner surface and the other with the red 

 outer surface of the lips, appeared much more distant from each 

 other than when they were in contact with the red surface only, 

 which has much greater tactile powers than the inner surface. 

 The same observation applies equally to the neighbouring 

 surface, differing much from each other in tactile power, viz. 

 the margin and the dorsum of the tongue, the volar and the 

 dorsal surfaces of the finger-points," &c. One result of Weber's 

 experiments is of great importance in a physiological point of 

 view : — " The tactile powers of any part of the skin are not, as is 

 generally imagined, directly proportioned to its sensibility ; thus 

 the mammae are easily tickled, and capable, when irritated, of 

 producing great pain ; in these respects they exceed any portion 

 of the trunk, and yet the skin of or round the nipples is but 

 very indifferently endowed with the faculty of touch, properly 

 so called. Indeed the same remark applies to the arm-pits, the 

 flanks, the soles of the feet, &c., and all ticklish parts of the skin 

 in general, as they are possessed of a comparatively slight power 

 of discriminating objects from each other by means of the touch. 

 Who was ever made to laugh by tickling the points of his 

 lingers ? and yet they are possessed of a tactile accuracy far ex- 

 ceeding that of any other portion of the skin !" 



This is a very curious subject of inquiry, and one not yet in- 

 vestigated. The reason of the matter is sufficiently obvious, 

 for parts endowed with the greatest tactile acumen are necessa- 

 rily much exposed, being so placed as to be brought with the 

 greatest facility into contact with external bodies, consequently, if 

 so disagreeable a sensation as that arising from tickling were easily 

 induced by this contact, those parts would be almost useless as 

 organs of touch. The experiments of Weber, considered with 

 reference to the researches made by Breschet on the structural 

 anatomy of the skin, render it extremely probable that the sense 

 of touch, properly so called, resides in a peculiarly constructed 

 apparatus, supplied with certain ramifications of the cutaneous 

 nerves, while the function of sensation, comprising the power of 



