NERVES OF SPECIAL SENSIBILITY. 389 
the amount of blood they contain ; since this blood may be 
sent to them for other purposes. Thus, it is a condition 
necessary to the action of Muscles, that they should be 
copiously supplied with blood (§ 591) ; but they are not 
acutely sensible: and Glands, also, the substance of which 
has very little sensibility, receive a large amount of blood for 
their peculiar purposes. 
488. But besides the general or common sensibility which is 
diffused over the greater part of the body of most animals, 
there are certain parts which are endowed with the property 
of receiving impressions of a peculiar or special kind, such as 
sounds or odours, which would have no influence upon the 
rest; and the sensations which these impressions excite, being of 
a kind very different from those already mentioned, arouse ideas 
in our minds such as we should never have formed without 
them. Thus, although we can gain a knowledge of the shape 
and position of objects by the touch, we could form no notion 
of their colour without sight, of their sounds without hearing, 
or of their odours without smell. 
489. The nerves which convey these special impressions 
are not able to receive those of a “ common ” kind : thus, the 
Eye, however well fitted for seeing, would not feel the touch 
of the finger, if it were not supplied with branches from the 
5th pair, as well as by the optic nerve. .Nor can the different 
nerves of special sensation be affected by impressions that are 
adapted to operate on others : thus, the ear cannot distinguish 
the slightest difference between a luminous and a dark object; 
nor could the eye distinguish a sounding body from a silent 
one, except by seeing its vibrations. But Electricity possesses 
the remarkable power, when transmitted along the several 
nerves of special sense, of exciting the sensations peculiar to 
each; and thus, by proper management, this single agent 
may be made to produce flashes of light, distinct sounds, 
a phosphoric odour, a peculiar taste, and a pricking feeling, 
in the same individual at one time. The inference which 
might hence be drawn—that Electricity and Nervous agency 
are identical-—is nevertheless premature, as will be shown 
hereafter (§ 585). 
