GENERAL SENSIBILITY. 599 



apartment ; although, on first entering from without, the attention may 

 have been attracted by them in a decided manner. A continuous and 

 uniform sound, like the steady rumbling of carriages, or the monotonous 

 hissing of boiling water, becomes after a time inaudible ; but as soon as 

 the sound ceases, we notice the alteration, and our attention is at once 

 excited. The senses, accordingly, receive their stimulus more from the 

 variation and contrast of external impressions, than from these impres- 

 sions themselves. 



Another important particular, in regard to the senses, is their capacity 

 for education. The touch can be so trained that the blind may read 

 words and sentences by its aid, in raised letters, where an ordinary 

 observer would hardly detect more than a slight inequality of surface. 

 The educated eye of the artist or the naturalist will distinguish varia- 

 tions of color, size, and outline, quite inappreciable to ordinary vision ; 

 and the senses of taste and smell, in those who are in the habit of 

 examining wines and perfumes, acquire a similar superiority of discrimi- 

 nating power. 



In these instances, it is not the organ of sense itself which becomes 

 more perfect in organization, or more susceptible to sensitive impres- 

 sions. The functional power, developed by cultivation, depends upon 

 the increased delicacy of the perceptive and discriminating faculties. 

 It is a mental and not a physical superiority which gives the painter or 

 the naturalist a greater facility for distinguishing colors and outlines, 

 and which enables the medical observer to detect nice variations in the 

 sounds of the heart or the respiratory murmur of the lungs. The 

 impressions of external objects, to produce their complete effect, must 

 first be received by a sensitive apparatus, which is perfect in organiza- 

 tion and functional activity ; and, secondly, they must be subjected to 

 the action of an intelligent perception, by which their nature, source, 

 and relations are fully appreciated. 



Beside the endowment of general sensibility distributed over the 

 integument, there are other faculties by which we appreciate particular 

 physical qualities or phenomena, namely, those of taste, odor, light, and 

 sound, the exercise of which is confined to special organs, having a struc- 

 ture adapted to that purpose alone. These are called the special senses. 

 Their organs differ from the general integument in their more compli- 

 cated structure and in the delicate and varied character of the functions 

 which they perform. They are incapable of feeling pain, similar to that 

 perceived by the nerves of general sensibilit}', though they may com- 

 municate disagreeable as well as pleasing impressions. The light, how- 

 ever intense, has no perceptible effect when allowed to fall upon the 

 skin, and causes a sensation only when admitted to the eye. The impres- 

 sion of sound is appreciated only by the ear, and that of odors only by 

 the olfactory membrane. These different sensations, therefore, are not 

 merely exaggerations of ordinary sensibility, but are peculiar in their 

 nature, and are in relation with distinct properties of external objects. 



