like care exercised by the nerves, by which all impressions
are transmitted to the brain. As the skin is continually exposed to
the influence of destructive agents, it is important that the nerves,
provided for its protection, should be kept in a healthy state.

649. A large proportion of the waste of the body passes through the
outlets of the skin; some portions in the form of oil, others in the
form of water and carbonic acid.

650. The oil-glands secrete an oil, partly free and diffused, and
partly mixed with albumen. When the cells are fully formed, that is,
fully distended, they yield their contents, and the fluid matter they
contain is set free, and passes along the tubes to the surface; this
fluid matter constitutes the oily element of the economy of the skin.

651. The uses of the unctuous product of the oil-glands are twofold:
1st. The protection; 2d. The removal of waste matter from the system.
In the exercise of these offices the oily substance is diffused over
those parts of the skin which are naturally exposed to vicissitudes of
temperature and moisture,--as the nose, face, and head;--to the
injurious attrition of contiguous surfaces,--as the flexures of
joints;--or the contact of acrid fluids,--as in the excoriations to
which infants are liable.

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

Give the illustration. 648. Why is it necessary that the cutaneous
nerves be kept in a healthy state? 649. Through what membrane does a
large proportion of the waste material of the system pass? 650. What
is the function of the oil-glands? 651. What are the uses of the oily
product of these glands?

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

652. The oil of the unctuous substance is the principal agent in
effecting these purposes: 1st. It prevents the evaporation or
congelation of the water of the cuticle, which would cause it to
become parched and peel off, thus leaving the sensitive skin exposed.
2d. It affords a soft medium to the contact of moving substances. 3d.
It repels moisture and fluids. 4th. The action of these glands removes
the waste atoms and purifies the blood.

653. In considering the purpose of the oily matter of the skin, there
are two situations in which it deserves especial remark. 1st. Along
the edges of the eyelids, where it is poured out in considerable
quantity. Here, it is the means of confining the tears and moisture of
the eyes within the lids, defending the skin from the irritation of
that fluid, and preventing th