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more widely separated when on a very sensitive part than they 
will elsewhere, or if drawn along the skin from a less to a more 
sensitive part will seem to separate as they approach the latter ; 
and, again, that a perfectly plane or level surface may he made 
to appear concave by another person drawing it over the tip 
of the finger of one whose eyes are covered, and pressing at 
first strongly, then lightly, and then strongly again, or it 
may be made to appear convex by reversing this order of 
pressure; but if the pressure is regulated by the subject of the 
experiment himself the delusion vanishes. Indeed, all these 
experiments ought to be performed on a person whose eyes are 
blinded, and by a second party. 
The extreme delicacy to which the sense of touch may be 
brought by practice often receives curious illustrations. One of 
the best known is the ability of the blind to read raised letters ; 
and in one case, when the sense of touch of the pulp of the 
fin gers had been much reduced by injury, the sufferer learned 
to read by applying her lips to the letters, ft is said that in 
counting rapidly a roll of bank-notes, a clerk in the Bank of Eng- 
land will be able to detect a conntei’feit note by the touch alone, 
which no examination by an ordinary individual could distinguish 
from a genuine note, even were he aware that it was forged. 
Such are some of the wonders of the sense of touch, — a sense 
whose impressions are conveyed to the mind by nerves set apart 
for that office, these nerves being the posterior roots of the 
spinal nerves, and the fifth and eighth cranial nerves. The fifth 
cranial is, indeed, a very singular nerve ; for, besides having 
motor fibres as well as sensitive, it has some of its sensitive 
fibres so modified, that in the papilla? of the tongue they be- 
come the nerves of the special sense of taste ; and indeed, in 
some of the invertebrate animals, as the crustaceans, this neiwe 
also receives the impressions of the special senses of sight and 
hearing. 
We come now to the function of secretion, and the description 
of the beautiful and complex apparatus by which that function 
is carried on. When we look with a simple lens, or even with 
the naked eye, at the delicate grooves crossing the furrows of the 
hand above mentioned, we find that a small orifice exists in the 
centre of each of them, sometimes occupying nearly the whole of 
the groove. This is, in fact, the orifice of a perspiratory duct ; and 
when the hand is warm the perspiration may be observed, even 
with the naked eye, to issue from it, forming minute shining dots. 
The glands by which the perspiration is secreted are seated at the 
under-surface of the true skin, each embedded in a cavity in it; 
and they consist, like many other glands, of a ravelled tube 
formed of basement membrane and epithelial scales, together 
with true secreting structure ; the materials for secretion being 
