ORGANS OF PERCEPTION. 169 
sation, (or a knowledge of the presence of objects), or if it 
includes, likewise, mtimations of their qualities. 
In order to excite to action the organs of touch, it is 
necessary that the body which communicates the impres- 
sion, be brought into contact with them ; and, in general, 
the more close and intimate the contact, the more correct 
is our information with regard to those qualities which it 
possesses, and which it is the business of touch to examime. 
Pressure appears to excite the nervous action of the organ, 
and when removed, that action ceases. Itis obvious, there- 
fore, that the perfection of any part, as an organ of touch, 
will depend, not only on its sensibility, but its plability, or 
power of applying itself to the unequal surfaces of bodies, 
and to its extent, to enable it to touch a large surface at 
once. 
The information communicated to the mind by the me- 
dium of touch, is more varied and extensive than that 
which is obtained by the aid of the other senses. It makes 
us acquainted with the dimensions of bodies,—their form, 
whether round or angular,—the condition of their swrface, 
whether rough or smooth,—their structure, whether hard 
or soft, fluid or solid,—their connection, whether moveable 
or immoveable,—their gravity, whether heavy or light,— 
and their sitwation, whether near or distant. 
These qualities, some of which are primary, and others 
secondary, are ascertained, by the organ of touch, in so cor- 
rect a manner, that we are scarcely ever deceived with the 
knowledge thus acquired. 
The accuracy of this sense is much improved by habit, 
and, in certain cases, where the other senses have been in- 
jured, as sight, this has acquired so great a degree of sen- 
sibility, as, in a great measure, to supply their loss. Thus, 
blind men are able to perceive their approach to a wall, by 
