nonvascular (without blood vessels) layer, the cuticle, or epidermis;
and (2) the deep vascular (with blood vessels) layer, the corium,
dermis, or true skin. (See Pl. XXXVIII, fig. 1.)
The cuticle is made up of cells placed side by side and more or less
modified in shape by their mutual compression and by surface evaporation
and drying. The superficial stratum consists of the cells dried in the
form of scales, which fall off continually and form dandruff. The deep
stratum (the mucous layer) is formed of somewhat rounded cells with
large central nuclei, and in colored skin containing numerous pigment
granules. These cells have prolongations, or branches, by which they
communicate with one another and with the superficial layer of cells in
the true skin beneath. Through these prolongations they receive nutrient
liquids for their growth and increase, and pass on liquids absorbed by
the skin into the vessels of the true skin beneath. The living matter in
the cells exercises an equally selective power on what they shall take
up for their own nourishment and on what they shall admit into the
circulation from without. Thus, certain agents, like iodin and
belladonna, are readily admitted, whereas others, like arsenic, are
excluded by the sound, unbroken epidermis. Between the deep and
superficial layers of the epidermis there is a thin, translucent layer
(septum lucidum) consisting of a double stratum of cells, and forming a
medium of transition from the deep spheroidal to the superficial scaly
cuticle.
The true skin, or dermis, has a framework of interlacing bundles of
white and yellow fibers, large and coarse in the deeper layers, and fine
in the superficial, where they approach the cuticle. Between the fibrous
bundles are left interspaces which, like the bundles, become finer as
they approach the surface, and inclose cells, vessels, nerves, glands,
gland ducts, hairs, and in the deeper layers fat.
The superficial layer of the dermis is formed into a series of minute,
conical elevations, or papillae, projecting into the deep portion of the
cuticle, from which they are separated by a very fine transparent
membrane. This papillary layer is very richly supplied with capillary
blood vessels and nerves, and is at once the seat of acute sensation and
the point from which the nutrient liquid is supplied to the cells of the
cuticle above. It is also at this point that the active changes of
inflammation are especially concentrated; it is the immediately
superposed cell layers (mucous) that become morbidly increased in the
earlier stages of inflammation; it is on the surface of the papillary
layer that the liquid is thrown out which raises the cuticle in the form
of a blister, and it is at this point mainly that pus forms in the
ordinary pustule.
The fibrous bundles of the true skin contain plain, muscular fibers,
which are not controlled by the will, but contract under the influence
of cold and under certain nervous influences, as in some skin diseases
and in the chill of a fever, and lead to contraction, tightening, or
corrugation of the skin, contributing to produce the "hidebound" of the
horseman. Other minute, muscular filaments are extended from the surface
of the dermis to the hair follicle on the side to which the hair is
inclined, and under the same stimulating influences produce that
erection of the hair which is familiarly known as "staring coat."
Besides these, the horse's skin is furnished with an expansion of red,
voluntary muscle, firmly attached to the fibrous bundles, and by which
the animal can not only dislodge insects and other irritants, but even
shake off the harness. This fleshy envelope covers the sides of the
trunk and the lower portions of the neck and head, the parts unprotected
by the mane and tail, and serves to throw the skin of these parts into
puckers, or ridges, in certain irritating skin diseases.
The hairs are cuticular products growing from an enlarged papilla lodged
in the depth of a follicle or sac, hollowed out in the skin and
extending to its deepest layers. The hair follicle is lined by cells of
epidermis, which at the bottom are reflected on the papilla and become
the root of the hair. The hair itself is formed of the same kind of
cells firmly adherent to one another by a tough, intercellular
substance, and overlapping each other, like slates on a roof, in a
direction toward the free end.
The sebaceous glands are branching tubes ending in follicles or sacs and
opening into the hair follicles, lined by a very vascular fibrous
network representing the dermis, and an internal layer of cells
representing the mucous layer of the cuticle. The oily secretion gives
gloss to the hair and prevents its becoming dry and brittle, and keeps
the skin soft and supple, protecting it at once against undue exhalation
of water and undue absorption when immersed in that medium. Besides
those connected with the hair follicles there are numerous, isolated,
sebaceous glands, opening directly on the surface of the skin, producing
a somewhat thicker and more odorous secretion. They are found in large
numbers in the folds of the skin, where chafing would be liable if the
surface were dry, as on the sheath, scrotum, mammary glands, and inner
side of the thigh, around the anus and vulva, in the hollow of the heel,
beneath the fine horn of the frog, on the inner side of the elbow, on
the lips, nostrils, and eyelids. When closed by dried secretion or
otherwise these glands may become distended so as to form various-sized
swellings on the skin, and when inflamed they may throw out offensive,
liquid discharges, as in "grease," or produce red, tender fungous
growths ("grapes.")
The sweat glands of the horse, like those of man, are composed of simple
tubes, which extend down through the cuticle and dermis in a spiral
manner, and are coiled into balls in the deeper layer of the true skin.
In addition to their importance in throwing offensive waste products out
of the system, these glands tend to cool the skin and the entire economy
of the animal through the evaporation of their watery secretion. Their
activity is therefore a matter of no small moment, as besides regulating
the animal heat and excreting impurities, they influence largely the
internal organs through the intimate sympathy maintained between them
and the skin.
Diseases of the skin may be conveniently divided, according to their
most marked features, into--
(1) Those in which congestion and inflammation are the most marked
features, varying according to the grade or form into (a) congestion
with simple redness, dryness, and heat, but no eruption (erythema);
(b) inflammation with red-pointed elevations, but no blisters
(papules); (c) inflammation with fine, conical elevations, each
surmounted by a minute blister (vesicle); (d) inflammation with a
similar eruption but with larger blisters, like half a pea and upwards
(bullae); (e) inflammation with a similar eruption, but with a small
sac of white, creamy pus on the summit of each elevation (pustules);
(f) the formation of pustules implicating the superficial layer of the
true skin, a small portion of which dies and is thrown off as a slough,
or "core" (boils); (g) the formation of round, nodular, transient
swellings in the true skin (tubercles); and (h) the excessive
production of scales, or dandruff (scaly or squamous affections).
(2) Diseases in which there are only deranged sensations of itching,
heat, tenderness, etc. (neurosis).
(3) Diseased growths, such as warts, callosities, horny growths, cancer,
etc.
(4) Diseases from parasites, animal and vegetable.
(5) Diseases connected with a specific poison, such as horsepox,
erysipelas, anthrax, farcy, or cutaneous glanders, etc.
(6) Physical injuries, like wounds, burns, scalds, etc.
CONGESTION (RED EFFLORESCENCE, OR ERYTHEMA).
This is a congested or slightly inflamed condition of the skin,
unattended with any eruption. The part is slightly swollen, hot, tender,
or itchy, and dry, and if the skin is white there is redness. The
redness is effaced by pressure, but reappears instantly when it is
removed. Except in transient cases the hairs are liable to be shed. It
may be looked on as the first stage of inflammation, and therefore when
it becomes aggravated it may merge in part or in whole into a papular,
vesicular, or pustular eruption.
Erythema may arise from a variety of causes, and is often named in
accordance with its most prominent cause. Thus the chilling, or partial
freezing, of a part will give rise to a severe reaction and congestion.
When snowy or icy streets have been salted this may extend to severe
inflammation, with vesicles, pustules, or even sloughs of circumscribed
portions of the skin of the pastern (chilblain, frost-bite). Heat and
burning have a similar effect, and this often comes from exposure to the
direct rays of the sun. The skin that does not perspire is the most
subject, and hence the white face or white limb of a horse becoming
dried by the intensity of the sun's rays often suffers to the exclusion
of the rest of the body (white face and foot disease). The febrile state
of the general system is also a potent cause; hence the white-skinned
horse is rendered the more liable if kept on a heating ration of
buckwheat, or even of wheat or maize. Contact of the skin with oil of
turpentine or other essential oils, with irritant liquids, vegetable or
mineral, with rancid fats, with the acrid secretions of certain animals,
like the irritating toad, with pus, sweat, tears, urine, or liquid
feces, will produce congestion or even inflammation. Chafing is a common
cause, and is especially liable to affect the fat horse between the
thighs, by the side of the sheath or scrotum, on the inner side of the
elbow, or where the harness chafes on the poll, shoulder, back,
breastbone, and under the tail. The accumulation of sweat and dust
between the folds of the skin and on the surface of the harness, and the
specially acrid character of the sweat in certain horses, contribute to
chafing or "intertrigo." The heels often become congested owing to the
irritation caused by the short, bristly hairs in clipped heels. Again,
congestion may occur from friction by halter, harness, or other foreign
body under the pastern, or inside the thigh or arm, or by reason of
blows from another foot (cutting, interfering, overreach). Finally,
erythema is especially liable to occur in spring, when the coat is being
shed, and the hair follicles and general surface are exposed and
irritable in connection with the dropping of the hairs.
If due only to a local irritant, congestion will usually disappear when
the cause has been removed, but when the feeding or system is at fault
these conditions must be first corrected. While the coat is being shed
the susceptibility will continue, and the aim should be to prevent the
disease from developing and advancing so as to weaken the skin, render
the susceptibility permanent, and lay the foundation of persistent or
frequently recurring skin disease. Therefore at such times the diet
should be nonstimulating, any excess of grain, and above all of
buckwheat, Indian corn, or wheat, being avoided. A large grain ration
should not be given at once on return from hard work, when the general
system and stomach are unable to cope with it; the animal should not be
given more than a swallow or two of cold water when perspiring and
fatigued, nor should he be allowed a full supply of water just after his
grain ration; he should not be overheated or exhausted by work, nor
should dried sweat and dust be allowed to accumulate on the skin or on
the harness pressing on it. The exposure of the affected heels to damp,
mud, and snow, and, above all, to melting snow, should be guarded
against; light, smooth, well-fitting harness must be obtained, and where
the saddle or collar irritates an incision should be made in them above
and below the part that chafes, and, the padding between having been
removed, the lining should be beaten so as to make a hollow. A zinc
shield in the upper angle of the collar will often prevent chafing in
front of the withers.
_Treatment._--Wash the chafed skin and apply salt water (one-half ounce
to the quart), extract of witch-hazel, a weak solution of oak bark, or
camphorated spirit. If the surface is raw use bland powders, such as
oxid of zinc, lycopodium, starch, or smear the surface with vaseline, or
with 1 ounce of vaseline intimately mixed with one-half dram each of
opium and sugar of lead. In cases of chafing rest must be strictly
enjoined. If there is constitutional disorder or acrid sweat, 1 ounce
cream of tartar or a teaspoon of bicarbonate of soda may be given twice
daily.
CONGESTION, WITH SMALL PIMPLES, OR PAPULES.
In this affection there is the general blush, heat, etc., of erythema,
together with a crop of elevations from the size of a poppy seed to a
coffee bean, visible when the hair is reversed or to be felt with the
finger where the hair is scanty. In white skins they vary from the
palest to the darkest red. All do not retain the papular type, but some
go on to form blisters (eczema, bullae) or pustules, or dry up into
scales, or break out into open sores, or extend into larger swellings
(tubercles). The majority, however, remaining as pimples, characterize
the disease. When very itchy the rubbing breaks them open, and the
resulting sores and scales hide the true nature of the eruption.
The general and local causes may be the same as for erythema, and in the
same subject one portion of the skin may have simple congestion and
another adjacent papules. As the inflammatory action is more pronounced,
so the irritation and itching are usually greater, the animal rubbing
and biting himself severely. This itching is especially severe in the
forms which attack the roots of the mane and tail, and there the disease
is often so persistent and troublesome that the horse is rendered
virtually useless.
The bites of insects often produce a papular eruption, but in many such
cases the swelling extends wider into a buttonlike elevation, one-half
to an inch in diameter. The same remarks apply to the effects of the
poison ivy and poison sumac.
_Treatment._--In papular eruption first remove the cause, then apply the
same general remedies as for simple congestion. In the more inveterate
cases use a lotion of one-half ounce sulphid of potassium in 2 quarts of
water, to which a little Castile soap has been added, or use a wash with
one-half ounce oil of tar, 2 ounces Castile soap, and 20 ounces water.
INFLAMMATION WITH BLISTERS, OR ECZEMA.
In this the skin is congested, thickened, warm (white skins are
reddened), and shows a thick crop of little blisters formed by effusions
of a straw-colored fluid between the true skin and the cuticle. The
blisters may be of any size from a millet seed to a pea, and often crack
open and allow the escape of the fluid, which concretes as a slightly
yellowish scab or crust around the roots of the hairs. This exudation
and the incrustation are especially common where the hairs are long,
thick, and numerous, as in the region of the pastern of heavy draft
horses. The term eczema is now applied very generally to eruptions of
all kinds that depend on internal disorders or constitutional conditions
and that tend to recurrences and inveteracy. Eczema may appear on any
part of the body, but in horses it is especially common on the heels and
the lower parts of the limbs, and less frequently on the neck, shoulder,
and abdomen. The limbs appear to be especially liable because of their
dependent position, all blood having to return from them against the
action of gravity and congestions and swellings being common, because of
the abundance of blood vessels in this part of the skin and because of
the frequent contact with the irritant dung and urine and their
ammoniacal emanations. The legs further suffer from contact with wet and
mud when at work, from snow and ice, from drafts of cold air on the wet
limbs, from washing with caustic soaps, or from the relaxing effects of
a too deep and abundant litter. Among other causes may be named
indigestion and the presence of irritant matters in the blood and sweat,
the result of patent medicated feeds and condition powders (aromatics,
stimulants), green food, new hay, new oats, buckwheat, wheat, maize,
diseased potatoes, smut, or ergot in grains, decomposing green feed,
brewers' grains, or kitchen garbage. The excitement in the skin, caused
by shedding the coat, lack of grooming, hot weather, hot, boiled, or
steamed feed conduces to the eruption. Lastly, any sudden change of feed
may induce it.
The blisters may in part go on to suppuration so that vesicles and
pustules often appear on the same patch, and, when raw from rubbing,
the true nature of the eruption may be completely masked. In well-fed
horses, kept in close stables with little work, eczema of the limbs may
last for months and years. It is a very troublesome affection in draft
stallions.
_Treatment._--This disease is so often the result of indigestion that a
laxative of 1 pound Glauber's salt in 3 or 4 quarts water or 1-1/2 pints
olive oil is often demanded to clear away irritants from the alimentary
canal. Following this, in recent and acute cases, give 2 drams of
acetate or bicarbonate of potash twice a day in the drinking water. If
the bowels still become costive, give daily 1 ounce sulphate of soda and
20 grains of powdered nux vomica. In debilitated horses combine the nux
vomica with one-half ounce powdered gentian root. As a wash for the skin
use 1 dram bicarbonate of soda and 1 dram carbolic acid in a quart of
water, after having cleansed the surface with tepid water. Employ the
same precautions as regards feeding, stabling, and care of harness as in
simple congestion of the skin.
In the more inveterate forms of eczema more active treatment is
required. Soak the scabs in fresh sweet oil, and in a few hours remove
these with tepid water and Castile soap; then apply an ointment of
sulphur or iodid of sulphur day by day. If this seems to be losing its
effect after a week, change for mercurial ointment or a solution of
sulphid of potassium, or of hyposulphite of soda, 3 drams to the quart
of water. In these cases the animal may take a course of sulphur (1
ounce daily), bisulphite of soda (one-half ounce daily), or of arsenic
(5 grains daily) mixed with 1 dram bicarbonate of soda.
INFLAMMATION WITH PUSTULES.
In this affection the individual elevations on the inflamed skin show in
the center a small sac of white, creamy pus, in place of the clear
liquid of a blister. They vary in size from a millet seed to a hazelnut.
The pustules of glanders (farcy buds) are to be distinguished by the
watery contents and the cordlike swelling, extending from the pustules
along the line of the veins, and those of boils by the inflammation and
sloughing out of a core of the true skin. The hair on the pustule stands
erect, and is often shed with the scab which results. When itching is
severe the parts become excoriated by rubbing, and, as in the other
forms of skin disease, the character of the eruption may become
indistinct. Old horses suffer mainly at the root of the mane and tail
and about the heels, and suckling foals around the mouth, on the face,
inside the thighs, and under the tail.
Pustules, like eczema, are especially liable to result from unwholesome
feed and indigestion, from a sudden change of feed--above all, from dry
to green. In foals it may result from overheating of the mare and
allowing the first milk after she returns, or by milk rendered
unwholesome by faulty feeding of the dam. If a foal is brought up by
hand the souring and other decompositions in the milk derange the
digestion and cause such eruption. Vetches and other plants affected
with honeydew and buckwheat have been the cause of these eruptions on
white portions of the skin. Disorders of the kidneys or liver are common
causes of this affection.
_Treatment._--Apply soothing ointments, such as benzonated oxid of zinc,
or vaseline with 1 dram oxid of zinc in each ounce. Or a wash of 1 dram
sugar of lead or 2 drams hyposulphite of soda in a quart of water may be
freely applied. If the skin is already abraded and scabby, smear thickly
with vaseline for some hours, then wash with soapsuds and apply the
above dressings. When the excoriations are indolent they may be painted
with a solution of lunar caustic 2 grains to 1 ounce of distilled water.
Internally counteract costiveness and remove intestinal irritants by the
same means as in eczema, and follow this with one-half ounce doses daily
of hyposulphite of soda, and one-half ounce doses of gentian. Inveterate
cases may often be benefited by a course of sulphur, bisulphite of soda,
or arsenic. In all, the greatest care must be taken with regard to feed,
feeding, watering, cleanliness, and work. In wet and cold seasons
predisposed animals should, so far as possible, be protected from wet,
mud, snow, and melted snow--above all, from that which has been melted
by salt.
BOILS, OR FURUNCLES.
These may appear on any part of the skin, but are especially common on
the lower parts of the limbs, and on the shoulders and back where the
skin is irritated by accumulated secretion and chafing with the harness.
In other cases the cause is constitutional, or attended with unwholesome
diet and overwork with loss of general health and condition. They also
follow on weakening diseases, notably strangles, in which irritants are
retained in the system from overproduction of poisons and effete matter
during fever, and imperfect elimination. There is also the presence of a
pyogenic bacterium, by which the disease may be maintained and
propagated.
While boils are pus producing, they differ from simple pustule in
affecting the deepest layers of the true skin, and even the superficial
layers of the connective tissues beneath, and in the death and sloughing
out of the central part of the inflamed mass (core). The depth of the
hard, indurated, painful swelling, and the formation of this central
mass or core, which is bathed in pus and slowly separated from
surrounding parts, serve to distinguish the boil alike from the pustule,
from the farcy bud, and from a superficial abscess.
_Treatment._--To treat very painful boils a free incision with a lancet
in two directions, followed by a dressing with one-half an ounce
carbolic acid in a pint of water, bound on with cotton wool or lint, may
cut them short. The more common course is to apply a warm poultice of
linseed meal or wheat bran, and renew daily until the center of the boil
softens, when it should be lanced and the core pressed out.
If the boil is smeared with a blistering ointment of Spanish flies and a
poultice put over it, the formation of matter and separation of the core
is often hastened. A mixture of sugar and soap laid on the boil is
equally good. Cleanliness of the skin and the avoidance of all causes of
irritation are important items, and a teaspoonful of bicarbonate of soda
once or twice a day will sometimes assist in warding off a new crop.
NETTLERASH (SURFEIT, OR URTICARIA).