iologists make a distinction between the sense of touch
and tact. Tact, or feeling, is more general, extending over the whole
surface of the skin and mucous membranes, while touch exists chiefly
in the fingers of man and in the noses of certain quadrupeds.

849. "In the exercise of these functions, tact is considered passive;
as, when any part of the system comes into contact with another body,
a sensation of its presence is given, without the exercise of
volition. On the contrary, touch is active, and is exercised
voluntarily, for the purpose of conveying to the mind a knowledge of
the qualities or properties of the surfaces of bodies; as when we feel
of a piece of cloth to ascertain its qualities, or a polished surface,
to prove its smoothness."

850. In man, the hand is admirably adapted to the exercise of touch.
"The fineness of the skin, its great sensibility, the species of
cushion formed by the sub-cutaneous fat at the extremities of the
fingers, the length and flexibility of these organs, and the
capability of opposing the thumb to the fingers, like a pair of
forceps, are so many conditions essentially favorable to the delicacy
of this sense, and enable us to appreciate with exactitude the
qualities of the bodies we may feel."

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846. Define sensation. How many senses have we? 847-851. _What is said
of the sense of touch?_ 847. Define touch. 848. What is the difference
between touch and tact? 849. In the exercise of these functions, which
is active, and which passive? 850. Why is the hand so admirably
adapted to the exercise of the sense of touch?

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851. The nerves that supply the sense of touch, proceed from the
anterior half of the spinal cord. Where this sense is most acute and
delicate, we find the greatest number of sensitive nervous filaments,
and those of the largest size.

_Observation._ In amputating limbs, and other surgical operations, the
division of the skin causes more pain than all the subsequent steps of
the operation, however protracted. The muscles, cellular membrane, and
fat have but little sensibility; while the bones, tendons, and
ligaments are insensible when not diseased, and may be cut without
causing pain.

HYGIENE OF THE SENSE OF TOUCH.

852. The sense of touch varies in different persons, and also in
individuals of different ages. Thus the sensibilities of the child are
more acute than those of the aged. Although there