COMPARISON BETWEEN TOUCH AND OTHER SENSES. 225 



us and make us err, if it did not guide our judgment." But 

 BufTon thought that "the difference between our senses 

 results only from the more or less external position of the 

 nerves, and from their greater or less number in the parts 

 which constitute the organs." The illustrious naturalist did 

 not recognize the special functions of the sensitive nerves; 

 the sensations of colours, of odours, of flavours, and of sounds, 

 were for him only tactile impressions. How could we admit 

 that feeling could guide us in judging of the colour of objects, 

 of their taste, their odour, or their sound ! Even while ad- 

 mitting that we can compare the excitation of the skin by 

 contact to that of the retina by the luminous waves, it is not 

 the less impossible to establish the least analogy between 

 touch and sight, since the retina is insensible to contact, and 

 as well as the optic nerve, conveys, not a tactile, but a 

 luminous impression to the brain. As for the other senses, 

 if air in vibration comes in contact with the tympanum of 

 the deaf man he perceives no sound, though he is sensible of 

 contact from foreign bodies on the tympanum ; if odoriferous 

 or savoury bodies come in contact with the pituitary mem- 

 brane or with the tongue of a man who has lost the sense of 

 smell or taste, he perceives neither odours nor flavours, al- 

 though he is perfectly aware of the presence of a foreign 

 body in the nose or mouth. 



The touch therefore cannot replace the other senses, 

 though it sometimes corrects their impressions, but it needs 

 to be constantly controlled and completed in the sensations 

 which it produces in us. If it enables us to learn form, 

 it is the eye which tells us of colour, and often perfects or 

 corrects our notions of distance, extent, and even of form; 

 as for instance, we distinguish less easily with the touch than 

 with the eye a sphere from an ellipsoid which is nearly 

 spherical. And besides it is when the touch has been exer- 

 cised under the control of the sight that it furnishes us with 

 the most exact ideas, for its results are then confirmed by 

 those which we possess already in regard to time, motion, 

 space, and the normal position of bodies, &c. Yet even in 

 these conditions the sense of feeling may be the source of 

 error. M tiller says, and rightly too, that by touch we feel not 



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