SENSATION. 375 



of the nervous system, but the auditory nerve can 

 convey that of sound ; and so of the rest.* 



In almost every case the impression made 

 upon the sentient extremity of the nerve which 

 is appropriated to sensation, is not the direct 

 eftect of the external body, but results from the 

 agency of some intervening medium. There is 

 always a portion of the organ of sense interposed 

 between the object and the nerve on which the 

 impression is to be made. The object is never 

 allowed to come into direct contact with the 

 nerves ; not even in the case of touch, where 

 the organ is defended by the cuticle, through 

 which the impression is made, and by which 

 that impression is modified so as to produce the 

 proper effect on the subjacent nerves. This ob- 

 servation applies with equal force to the organs 

 of taste and of smell, the nerves of which are 

 not only sheathed with cuticle, but defended 

 from too violent an action by a secretion ex- 

 pressly provided for that purpose. In the 

 senses of hearing and of vision, the changes 



* The credulity of the public has sometimes been imposed 

 upon by persons who pretended to see by means of their fingers : 

 thus, at Liverpool, the celebrated Miss M'Avoy contrived for a 

 long time to persuade a great number of persons that she really 

 possessed this miraculous power. Equally unworthy of credit 

 are all the stories of persons, under the influence of animal 

 magnetism, hearing sounds addressed to the pit of the stomach, 

 and reading the pages of a book a])plied to the skin over that 

 organ. 



