Those impressions of touch must have been communicated, with their extremely nice distinctions, to the sensitive nerves that lie underneath the skin, and must have been transmitted all the way through the arm to the brain, although the touch itself was so light as scarcely to be appreciable with regard to the force applied.
A hair lying on the tongue will be plainly perceptible to the touch of the tongue; and the surface of a broken tooth will often cause the tongue great annoyance, by the acute perception it imparts of the roughness of its surface.
The toes are also highly sensitive, though their powers of touch are seldom fully developed. Persons who have lost their arms, however, have brought their feet to be almost as sensitive as fingers. Blind persons increase, by constant exercise, their powers of touch to such a degree that they are able to read freely by passing their fingers over embossed printing; and they have been known to distinguish colours by differences in their grain, quite unappreciable by other persons.
1006. Why is feeling impaired when the hands are cold?
Because, as the blood flows slowly to the nerves, they are less capable of that perception of touch which is their special sense. The skin contracts upon the nervous filaments, and impairs the contact between them and the bodies which they touch.
1007. Why do the fingers prick and sting when they again become warm?
Because, as the warmth expands the cuticle, and the blood begins to flow more freely through the vessels, the nerves are made conscious of the movements of the blood, and continue to be so until the circulation is equally restored to all the parts.
"In the sweat of thy face shalt thou eat bread, till thou return to the ground; for out of it thou wast taken: for dust thou art, and unto dust shalt thou return."—Genesis iii.