ing, together with a more nutritious
diet.

582. _The surplus heat should be removed equally from all parts of the
system._ The rapid evaporation of fluids, as in free perspiration, or
from radiation, as in a cold atmosphere, is attended with a removal of
heat from the system. This modifies the action of the circulatory
vessels. Consequently, if heat is suddenly and rapidly abstracted from
one part of the system, the equilibrium of the circulation is
destroyed, which will produce disease.

-=-=-=-=-=-=-=-=-=-=-=-=

Why do we, then, require more clothing in winter than in summer? 581.
Why do persons of firm health and vigorous constitutions need less
clothing than those who are feeble? What is a general practice among
infirm persons? What would be more judicious? 582. Why should the
surplus heat be removed equally from all parts of the system? What is
said respecting currents of air from small apertures?

-=-=-=-=-=-=-=-=-=-=-=-=

_Observation._ Currents of air that impinge upon small portions of the
body, as from small apertures, or from a window slightly raised,
should be avoided. They are more dangerous than to expose the whole
person to a brisk wind, because the current of air removes the heat
from the part exposed, which disturbs the circulation of blood and
causes disease, usually in the form of "colds." For the same reason,
it is not judicious to stand in an open door, or the opening of a
street.

583. _The system suffers less when the change of temperature is
gradual._ The change in the production of heat, as well as in the
evaporation of fluids from the system, is gradual when not influenced
by foreign causes. This gradual change is known under the name
_acclimation_. By this means the body is enabled to endure tropical
heat and polar cold. Owing to this gradual adaptation of the system to
different temperatures, we can bear a greater degree of heat in the
summer between the tropics, than in the winter under the polar
circles. On the other hand, we can endure a greater degree of cold in
winter and in the arctic region, than in the summer and in equatorial
countries.

584. The sensation of heat which would be oppressive in a mild, warm
day of January, would only be grateful in July, and a degree of cold
which could scarcely be endured in August, would not be uncomfortable
in December. The changes of season in our latitude prevent the
disagreeable and perhaps fatal consequence that would follow, if n