piratory ducts, and diminishes
the action of their glands; consequently, less heat is generated. For
this reason, the hands or feet when clean are less liable to become
chilled or frozen.

677. _The sensitiveness of the skin to the influence of cold, is much
modified by habit._ A person who has been habituated to the
temperature of a warm room, or warm climate, suffers more when exposed
to cold, than an individual who has been accustomed to colder air.
Thus a person who labors or studies in a warm room, should wear more
clothing when exposed to the air, while walking or riding, than an
individual who labors in a cooler atmosphere. Not only is the
sensibility of the skin increased by a warm atmosphere, but the
activity of the digestive, respiratory, and nervous systems, in
generating heat, is much diminished. This is an additional reason why
an increased amount of clothing is demanded during exposure to cold
air. In all cases where practicable the heat of the system should be
maintained by exercise, in preference to the use of fur or flannel.

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675. Why does the person of active habits require less clothing than
one of sedentary employments? 676. Why do we need less clothing when
the skin is clean? 677. Show the effect of habit on the sensitiveness
of the skin.

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678. _Those parts of the skin usually covered, uniformly need that
protection._ The power of generating heat is diminished, and the
impressibility to cold is increased, on those portions of the skin
usually clothed. If a person wears the dress high and close about the
neck, he suffers from exposure to a cold atmosphere if a dress is worn
that is not as high or more open. As a general rule, it is preferable
that those parts of the system, as the larynx, be exposed that are not
uniformly protected by clothing.

679. _The clothing should be kept clean._ No article of apparel is
entirely free from absorption; even wool and cotton possess it in a
small degree. They take up a portion of the transpired fluids which
contain saline and animal matter, and thus the fibres of the garments
become covered with the cutaneous excretions. We are practically aware
of the retention of these secretions from the soiled appearance of
those garments worn next the skin, which are so covered as to preclude
the particles of dust from lodging upon them.

680. The porosity of the clothing is lessened when soiled, and its
power