e skin is inactive, since sweat is
continually passing from the surface, though often it may not be apparent.
On an average from 1-1/2 to 4 pounds of sweat are eliminated daily from
the skin in the form of vapor. This is double the amount excreted by the
lungs, and averages about 1/67 of the weight of the body.

The visible sweat, or sensible perspiration, becomes abundant during
active exercise, after copious drinking of cold water, on taking certain
drugs, and when the body is exposed to excessive warmth. Forming more
rapidly than it evaporates it collects in drops on the surface. The
disagreeable sensations produced by humid weather result from the fact
that the atmosphere is so loaded with vapor that the moisture of the skin
is slowly removed by evaporation.

Experiment 124. Study the openings of the sweat glands with the aid
of a strong magnifying glass. They are conveniently examined on the
palms.

A man's weight may be considerably reduced within a short time by loss
through the perspiration alone. This may explain to some extent the
weakening effect of profuse perspiration, as from night sweats of
consumption, convalescence from typhoid fever, or the artificial sweating
from taking certain drugs.

241. The Skin as a Regulator of the Temperature of the Body. We thus
learn that the skin covers and protects the more delicate structures
beneath it; and that it also serves as an important organ of excretion. By
means of the sweat the skin performs a third and a most important
function, _viz_., that of regulating the temperature of the body.

The blood-vessels of the skin, like those of other parts of the body, are
under the control of the nervous system, which regulates their diameter.
If the nervous control be relaxed, the blood-vessels dilate, more blood
flows through them, and more material is brought to the glands of the skin
to be acted upon. External warmth relaxes the skin and its blood-vessels.
There results an increased flow of blood to the skin, with increased
perspiration. External cold, on the other hand, contracts the skin and its
blood-vessels, producing a diminished supply of blood and a diminished
amount of sweat.

Now, it is a law of physics that the change from liquid to vapor involves
a loss of heat. A few drops of ether or of any volatile liquid placed on
the skin, produce a marked sense of coldness, because the heat necessary
to change the liquid into vapor has been drawn rapidly fr