J- ,' ■ 



SENSATION, r ill! 337 



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 appro- 

 priated to sensation, is not the direct effect of tlie 

 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 observation 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 expressly 

 provided for that purpose. In the senses of hear- 

 ing and of vision, the changes which take place in 

 the organs interposed between the external im- 

 pressions and the nerves, are still more remarkable 

 and important, and will be respectively the subjects 

 of separate inquiries. The objects of these senses, 

 as well as those of smell, being situated at a dis- 

 tance, produce their first impressions by the aid 



* The credulity of the pubhc 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 

 applied to the skin over that organ. 



VOL. II. Z 



