strated by
noting the effects of cold upon the cutaneous tissue, the application
of which contracts the blood-vessels, and drives the circulating fluid
from this membrane, which is shown by the paleness, as well as by the
shrivelled appearance of the skin. And, if this tissue is wounded
while under the influence of cold, but little pain will be felt, and
this chilling influence may be carried so far as not only to deprive
the part of sensation, but of vitality.

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854. Mention other conditions that affect these nerves. 855. What is
the effect of the varying health or condition of the brain upon the
sensitiveness of the skin? Give instances of this effect. 856. What is
the result if a nervous trunk is divided or compressed? How may
"numbness" in the limbs be produced? 857. Does the quantity of blood
supplied to the skin affect its sensibility?

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858. The influence of the blood upon the sensibility of the skin, is
further demonstrated by the pain experienced when chilled extremities
are suddenly exposed to heat. The nerves, by the sudden dilatation of
the contracted blood-vessels, are put in vivid and rapid motion, which
causes the painful and tingling sensation that we experience. In every
part of the system, sudden changes produce unpleasant sensations, and
frequently a diseased condition of the organs.

_Observation._ When the hands, or other portions of the body, are
frozen, or severely chilled, safety and comfort demand that
circulation be restored to the parts by moderate exercise in a cool
room. Not unfrequently, the vitality of the limb is destroyed by
immersing it in hot water or holding it near the fire.

859. _The quality of the blood also influences sensation._ If the
brain and other parts of the nervous system receive impure blood,
their energy is depressed, and the sensibility of the skin rendered
more or less obtuse.

860. _The condition of the cuticle modifies the impression made upon
the cutaneous nerves._ 1st. When the cuticle has become thick and
hard, like horn, as on the inside of the mason's hand, it enables him
to ply his tools without much suffering, because the thickened cuticle
diminishes the impressions made upon the nerves.

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How is it demonstrated? 858. How is the influence of the blood upon
the skin further demonstrated? How should circulation be restored to
limbs frozen or severely chilled? What shoul