not clearly known, unless it be from the sudden retention of
poisonous exhalations.

243. The Skin and the Kidneys. There is a close relationship between
the skin and the kidneys, as both excrete organic and saline matter. In
hot weather, or in conditions producing great activity of the skin, the
amount of water excreted by the kidneys is diminished. This is shown in
the case of firemen, stokers, bakers, and others who are exposed to great
heat, and drink heavily and sweat profusely, but do not have a relative
increase in the functions of the kidneys. In cool weather, when the skin
is less active, a large amount of water is excreted by the kidneys, as is
shown by the experience of those who drive a long distance in severe
weather, or who have caught a sudden cold.

[Illustration: Fig. 104.--Magnified View of a Sweat Gland with its Duct.

The convoluted gland is seen surrounded with big fat-cells, and may be
traced through the dermis to its outlet in the horny layers of the
epidermis.]

244. Absorbent Powers of the Skin. The skin serves to some extent as
an organ for absorption. It is capable of absorbing certain
substances to which it is freely exposed. Ointments rubbed in, are
absorbed by the lymphatics in those parts where the skin is thin, as in
the bend of the elbow or knee, and in the armpits. Physicians use
medicated ointments in this way, when they wish to secure prompt and
efficient results. Feeble infants often grow more vigorous by having their
skin rubbed vigorously daily with olive oil.

A slight amount of water is absorbed in bathing. Sailors deprived of
fresh water have been able to allay partially their intense thirst by
soaking their clothing in salt water. The extent to which absorption
occurs through the healthy skin is, however, quite limited. If the outer
skin be removed from parts of the body, the exposed surface absorbs
rapidly. Various substances may thus be absorbed, and rapidly passed into
the blood. When the physician wishes remedies to act through the skin, he
sometimes raises a small blister, and dusts over the surface some drug, a
fine powder, like morphine.

The part played by the skin as an organ of touch will be considered
in sections 314 and 315.

Experiment 125. _To illustrate the sense of temperature_. Ask the
person to close his eyes. Use two test tubes, one filled with cold and
the other with hot water, or two spoons, one hot and one cold. Apply
each to different part