216 On the Anatomy and Physiology of the Organs of the Senses. 



trouble or special attention of the mind, that we derive full benefit from 

 our senses, and are enabled to arrive at those conclusions respecting the 

 distance and relations of bodies, that seem to be intuitive, but which are 

 the results of long and constant habit. 



In the arrangement of the sensorial functions, it seems simplest and most 

 philosophical to consider them as modifications of tact. The organ of tact 

 consists of a series of minute nervous filaments, expanded over the whole 

 surface of the body, and shielded by a delicate veil of integument, from 

 any rude or injurious impression. Taste is evidently a species of touch, 

 of a higher character indeed, since it takes cognizance of certain properties 

 of bodies which tact cannot, and it is confined to a particular and limited 

 portion of the animal. It does not supersede, but is superadded to the 

 former sense, and requires the presentation of its object under somewhat 

 different circumstances. 



The next sense, that of smell, resembles in many respects that of taste j 

 requiring only the presentation of its subjects in a gaseous, instead of an 

 aqueous vehicle. This sense is however superior to the other two, inso- 

 much as by it the sphere of perception is more enlarged, since it takes 

 cognizance of effluvia, which may proceed from bodies at a considerable 

 distance. 



The senses of hearing and vision are of a superior character, and more 

 generally interesting, since they involve the cultivation of two well known 

 physical sciences, acoustics and optics. Hearing is obviously only a refined 

 species of touch, the sense being excited by the vibrations of the atmos- 

 phere upon the acoustic nerve. 



The sense of sight is superior to all the rest, both in the number of the 

 properties of a body, which it is able by cultivation to take notice of, and 

 more especially on account of the distance at which its impressions may 

 be received. And if the undulatory theory concerning the nature of light, 

 that generally received, be correct, the function of vision must be con- 

 sidered just as much a modification of tact, as those of taste, smell, or 

 hearing. 



We have said that with the exception of the eye, the facts observed 

 respecting the uses of the parts composing the organs of sense, have not 

 been sufficiently well ascertained, to lead to any grand conclusions in ana- 

 tomical or physiological science ; tliat such will sooner or later take place, 

 is no doubt very possible, but it is not in the present state of our know- 

 ledge very probable. But so far as the uses of any parts have been dis- 

 covered, they have been ever in strict accordance v\ ith truths, derived from 

 other sources. Thus, when DoUand invented the achromatic lens, he 

 found that the chromatic difficulty had been already overcome in the eye ; 

 and when Mr. Wheatstone discovered that a change in the plane of the 

 motion of a wave of sound weakens its intensity, the canals within the ear 

 were found to be so disposed as to obviate such a change : and we cannot 



