56 TOUCH AND SENSATION* 



suppose it an exception to the principle laid down, 

 that no single part can execute more than a single 

 direct function. In reality, however, it is only by 

 taking the guidance of this principle that we can ex- 

 tricate ourselves from the apparent confusion. We 

 have already seen that exhalation, and the regulation 

 of heat and absorption, are each connected with dis- 

 tinct textures in the skin. On further examination, 

 we shall find the office of Touch and Sensation in- 

 trusted exclusively to another constituent part, the 

 nervous; for, in serving as the instrument of.feeling, 

 the skin acts in no other way than by affording a 

 suitable surface for the distribution and protection 

 of the nerves which receive and transmit to the 

 brain and mind the impressions made on them by 

 external bodies. In this respect the skin resembles 

 the other organs of sense ; in all of which the nerve 

 is the true instrument of the sense, and the eye, the 

 ear, the nose, and the skin are simply structures fitted 

 to bring the nerve into relation with the qualities of 

 colour, sound, smell, roughness, or smoothness, by 

 which they are respectively affected ; and they 

 differ from each other, because sound differs from 

 colour, colour from smell, and smell from roughness 

 or smoothness ; and because sound or colour can be 

 taken cognizance of by its own nerve only when 

 the latter is provided with an apparatus fit to be 

 acted upon by the vibrations of the air, or by the 

 rays of light. In every instance, it is the external 

 object acting upon a nerve which gives rise to the 

 mpression received from the organs of sense. 



Every part of the skin, however remote, is pro- 

 vided with filaments from the nerves of sensation, 

 in order that we may become immediately sensible 

 of the presence and action of external bodies. If 

 any part were destitute of this property, its texture 

 and vitality might be destroyed without our con- 

 sciousness of the fact ; whereas, in consequence of 

 this provision of sensitive nerves, no object can 



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