ner, and directed toward the root of the hair; so that, if a
hair be rolled between the fingers, it moves only in one direction.

[Illustration: Fig. 118. The hair follicle (1) is represented as imbedded
in the cellular membrane, (2,) which is situated beneath the skin. 3, 3,
The membranous sac, which has a narrow neck, opening externally by a
contracted orifice, through which the hair (4) passes. Its internal
surface is smooth, and not adherent to the hair, but separated from it by
a reddish fluid. From the bottom of the sac (5) the pulp of the hair
arises, and passes through the skin at 6.]

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717-723. _Describe the appendages of the skin._ 717. Why have not
hairs vitality? Where do they take their origin? Give their structure.
What is represented by fig. 118?

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718. The color of the hair varies in different individuals, and is
generally supposed to depend on the fluids contained in the pith.
There are two causes which act in changing the hair gray. The first
is, defective secretion of the coloring fluid. The second is, the
canals, which convey the fluid into the hair, become obliterated. In
the first instance, the hair will remain; in the second, it dies, and
drops out; the cuticle of the scalp grows over the canal, which is
soon obliterated, and the head becomes bald.

_Observation._ It is related that the hair of Marie Antoinette, Queen
of France, and others, from excessive mental agitation, changed from
black to gray in a single night. This is not strictly true; the
secretion may be arrested, but that already deposited in the pith will
require days or weeks to be removed.

719. Upon the upper part of the head, the oil-tubes open into the
hair-sacs; consequently, the secretion of the oil-glands is spread
over the surface of the hair, and not upon the cuticle. This is the
cause of the dry, white, branny scales, called "scurf," or "dandruff,"
upon the head. This is natural, and cannot be prevented. When scurf
exists, the only necessary application to remove it, is the frequent
use of the hair-brush, and washing with pure water.

_Observation._ The secretion of the oil-glands may become impacted
around the hairs as they issue from the skin, and thus prevent their
outward movement in growing. The pressure of the matter deposited at
their bulbs will then cause itching. The comb and the brush may be
used to remove the impacted matter, and relieve the disagreea