tly thought of are those which pour out the perspiration. These
have a double function. In the first place they assist in keeping the
temperature of the body uniform. When we are too warm they pour out a
watery fluid over the surface of the body. If the air is dry enough
and our body not too closely protected by clothing, this perspiration
passes off in the form of vapor. All evaporation requires heat, which
in this case is extracted from the body. So soon as the temperature
returns to its normal level the flow of perspiration ceases. The other
function of the sweat glands is to take from the blood some of the
waste matters of the body and pour them out upon the surface. This is
done in order that the body may free itself from substances which, if
they were to accumulate, would have a poisonous effect upon its
action. It is this function of the sweat glands which makes it
necessary for us to bathe the surface of our bodies with water. Dirt,
in the ordinary sense of the word, is not harmful to a sound skin. Our
reason for bathing is really to remove the wastes which we ourselves
have poured upon the surface of the skin. These, if allowed to remain,
soon decompose, like all nitrogenous substances, and become very
offensive. They may then be reabsorbed into the skin and nature's
effort to throw them off has been in vain. These glands, since they
contain waste matter, could not possibly yield food for the young.
They would poison and not nourish. Hence, whatever the breasts may be,
they are not altered sweat glands.

There is another set of organs in the mammalian skin. At the base of
each hair lies an oil gland. The function of these is to pour out a
substance which spreads along each hair and over the surface of the
body. The outside of the skin is always dead, and would easily crack
were it not for the constant secretion of this oil. In winter, when
the blood circulates less freely and these glands consequently pour
out less oil, the supply frequently runs short. If what little is
poured out is too frequently removed by washing, the skin becomes
brittle, and, on bending a joint, the epidermis cracks. The gloss of
the hair is due to the oil thus poured out. This oil becomes one
ingredient in the milk produced by the transformed gland. But there
is another important constituent. When one does unaccustomed manual
work the ordinary result is the formation of a blister. The epidermis,
or scarfskin, becomes detached from the d