t was adequate to prevent chills while
awake, contracts a cold, unless he throws over him an additional
covering.

579. _The state of the skin exercises much influence in the generation
of heat._ If the functions of this membrane are not interrupted, more
heat will be generated than when it is pallid and inactive. The action
of the capillaries is most energetic when the skin is clean; on this
account, before taking a walk or a ride, in cold weather, remove all
impurities from the skin, by thorough ablution and vigorous friction.

580. _The amount and kind of clothing modify the temperature of the
system._ Those persons that are well clothed have greater power to
resist cold than the thinly apparelled, because both the evaporation
and the radiation from the skin are impeded, and less heat, in
consequence, is abstracted from the body. If the articles of apparel
possess the property of retaining air in their meshes, as flannel, the
removal of heat is not as rapid as when linen is worn.

_Observation._ In winter, although more heat is generated in the
system than in summer, yet we require more clothing, and also those
articles that are poor conductors of heat, because caloric is more
rapidly extracted in clear, cold weather, than in a warm day.

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What does the preceding remark explain? 579. What suggestion
respecting the condition of the skin before taking a walk or ride in a
cold day? Why? 580. Do the amount and kind of clothing affect animal
heat? What is said of well-clothed persons? When does the system
generate the most heat?

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581. _The health and constitution influence the generation of heat._
When the health is firm, and the constitution vigorous, less clothing
is needed, for the change among the particles of matter is more rapid,
and more heat is generated, than when the opposite condition obtains.
Persons of a feeble constitution, particularly, if any of the vital
organs[18] are diseased, need more clothing and require rooms of a
warmer temperature, than individuals who are free from disease and
have a vigorous constitution.

[18] The brain, lungs, heart, and digestive organs, are called _vital_
organs.

_Observation._ Persons who are infirm, and whose vital powers are
feeble, in general, accustom themselves to an undue amount of clothing
and warm rooms. A more judicious practice would be, to exercise more
and use a moderate amount of cloth