APPENDAGES OF THE SKIN.
717. The HAIRS are appendages of the skin, and, like the cuticle, they
are a product of secretion. They have no blood-vessels or nerves, and,
consequently, no vitality. The hairs take their origin from the
cellular membrane, in the form of bulbs. Each hair is enclosed beneath
the surface by a vascular secretory follicle, which regulates its form
during growth. In texture, it is dense, and homogeneous toward the
circumference, and porous and cellular in the centre, like the pith of
a plant. Every hair has on its surface pointed barbs, arranged in a
spiral manner, 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 disagreeable
sensation.
720. The oil is most abundant near the roots of the hair A free use
of the brush spreads it along the hairs, and gives them a smooth,
glossy appearance. Soap should rarely be used in washing the head, as
it will remove the oil which is essential to the health and appearance
of the hair.
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718. Upon what does the color of the hair depend? What are the causes
of the hair becoming gray? What is the cause of the hair dropping out?
What is related of Marie Antoinette? 719. How is "dandruff" on the
scalp produced? What is the only necessary application to remove it?
Give observation. 720. Where is the oil of the hair most abundant?
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721. The uses of the hair vary in different regions of the body. Upon
the head, it aids in shielding the brain from injury by blows, and it
likewise serves to protect this part of the system from heat and cold,
thus maintaining equal temperature of the cerebral organ. About the
flections of the joints, as in the axilla, (armpit,) they prevent
irritation of the skin from friction; in the passages to the ears and
nostrils, they present an obstacle to the ingress of insects and
foreign bodies; while in the eyebrows and eyelids, they serve to
protect the organ of vision.
[Illustration: Fig. 119. A section of the end of the finger and nail. 4,
Section of the last bone of the finger. 5, Fat, forming the cushion at
the end of the finger. 2, The nail. 1, 1, The cuticle continued under and
around the root of the nail, at 3, 3, 3.]
722. The NAILS are hard, elastic, flexible, semi-transparent scales,
and present the appearance of a layer of horn. The nail is divided
into the _root_, the _body_, and the _free portion_. The root is that
part which is covered on both surfaces; the body is that portion which
has one surface free; the free portion projects beyond the end of the
finger.
723. The nail is formed of several laminae, or plates, that are fitted
the one to the other; the deepest is that which is last formed. The
nails, as well as the hoofs of animals and the cuticle, are products
of secretion. They receive no blood-vessels or nerves. If the cuticle
be removed in severe scalds they will separate with it, as the hoofs
of animals are removed by the agency of hot water. The nails increase
in length and thickness, by the deposition of albumen upon their under
surface, and at their roots, in a manner similar to the growth of the
cuticle, of which they constitute a part.
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How can it be spread along the hairs? Why should soap not be used in
washing the hair? 721. Of what use is the hair upon the head? About
the flexions of the joints? In the nasal and ear passages? Upon the
eyebrows and eyelids? 722. Describe the nails. 723. How are they
formed?
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_Observations._ 1st. The nail upon its under surface is fashioned into
thin vertical plates, which are received between the folds of the
sensitive skin. In this manner, the two kinds of laminae reciprocally
embrace each other, and the firmness of connection of the nail is
maintained. If we look on the surface of the nail, we see an
indication of this structure in the alternate red and white lines
which are there observed. The former of these correspond with the
sensitive laminae; the latter with the horny plates. The ribbed
appearance of the nail is due to the same circumstance. These
sensitive laminae are provided with an unusual number of capillary
vessels for the formation of the nail, and hence they give a red tint
to the portion under which they lie.
2d. Near the root of the nail there is a part that is not laminated,
and it is less abundantly supplied with blood-vessels. This portion
consequently looks pale compared with the laminated portion, and from
its half-moon shape is technically termed _lunula_. Beyond the lunula,
the root of the nail is imbedded in the fold of the sensitive skin,
and has the same relation to that structure that any single one of the
thin horny plates of its under surface has to its corresponding pair
of sensitive laminae.
724. The nails, from their position, are continually receiving
knocks, which produce a momentary disturbance of their cell
formation, followed by a white spot. The care of the nails should
be strictly limited to the knife or scissors, to their free border,
and an ivory presser, to prevent adhesion of the free margin of the
scarf-skin to the surface of the nail. This edge of the cuticle
should never be pared, the surface of the nail never scraped, nor the
nails cleaned with any instrument whatever, except the nail-brush,
aided by water and soap. An observance of these suggestions, will
prevent irregularities and disorders of the nails.
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Give observation 1st. Observation 2d. 724. How should the nails be
treated to prevent irregularities and disease?
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_Observations._ 1st. When we wear a shoe that is too short for the
foot, the edge of the nail is brought against the leather. This
interrupts the forward growth of the nail, and it spreads out on the
sides, and becomes unusually thick. It then presses upon the soft
parts, and is said to "grow into the flesh." The prevention is, to
wear shoes of ample size.
2d. Instances are by no means unfrequent in which the power of
production of the nail at the root becomes entirely destroyed, and it
then grows in thickness only. When this affection occurs, it is often
remarkable what a mass the nail presents. Instances are on record,
where the nail is regularly shed; and, whenever the old nail falls
off, a new one is found beneath it, perfectly formed. Sometimes the
growth in length is not entirely checked, although growth in thickness
is induced; the nail then presents a peculiar appearance.
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What causes the edge of the nail "to grow into the flesh" of the toe?
How prevented?
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