GENERAL DISCUSSION.—The two layers that form the skin are the epidermis and the derma. The cells of the outer layer or epidermis are of two kinds. The superficial portion is formed by horny, flattened cells and the deeper by softer cells. This layer of the skin varies greatly in thickness in the different species. The derma is composed of some muscular fibres interwoven with the connective-tissue fibres. It contains the roots of the hair follicles, sweat and oil glands. The external face which is covered by the epidermis shows a multitude of little elevations. These are the vascular and nervous papillae. In addition, it shows openings through which the hairs and the skin glands pass. The inner surface is united more or less closely to the muscular or underlying tissue by a layer of fibro-fatty tissue.

The appendages of the skin are the hairs and horny productions. The horny productions comprise the horns, chestnuts, ergots, claws and hoofs.

The hair varies in length, thickness and coarseness in the different species, and the different regions of the body. In addition, breeding, care, heat and cold may cause marked variations in the thickness of the coat. Exposure to cold causes the coat to thicken. High temperatures cause the short hairs to drop out and the coat to become thin.

Diseases of the skin may be classified as parasitic and non-parasitic. Parasitic skin diseases are caused by animal and vegetable parasites. Non-parasitic skin diseases are caused by irritation to the skin and internal causes. Irritation to the skin may be either chemical, thermic or mechanical. The internal causes may be due to an individual predisposition together with digestive disturbances and the eating of feeds too rich in protein. In this chapter parasitic skin diseases produced by insects will not be discussed.

FALLING OUT OF THE HAIR AND FEATHERS.—Falling out of the hair and feathers frequently occurs independent of parasitic diseases. This condition does not occur as an independent disorder, but as a secondary affection. It is due to faulty nutrition, and irritation to the skin. Intestinal diseases, insufficient feed and feed of bad quality are common causes. Animals that are fed a heavy ration, or that lie on dirty, wet bedding frequently lose large patches of hair. Sheep that are dipped in late fall and early winter, or exposed to wet, cold weather may lose a part of their fleece. It is not uncommon for animals toward the latter period of pregnancy, or that sweat freely, to lose patches of hair.

Falling out of the hair heals of itself within a few weeks.

The preventive measures are of special importance in sheep and horses. This consists in avoiding conditions that may lead to alopecia and in correcting the diet. In horses the regions of the mane and tail should be washed with soap, or rubbed with alcohol and spirits of camphor, equal parts. Treatment should be persisted in for a long period if necessary.

URTICARIA, "NETTLERASH."—Urticaria is characterized by roundish elevations that appear quickly and become scattered over a part or the whole surface of the skin. They are caused by an inflammatory infiltration of the deeper layers of the skin. Horses and hogs are most frequently affected.

The causes of urticaria are irritating juices of certain plants, secretions of flies, ants and some caterpillars, irritating drugs, scratching, sweating and the action of cold on a warm skin. It has been observed in connection with the feeding of certain leguminous feeds and digestive disturbances. Horses that are fat, or putting on flesh rapidly, seem to be predisposed to this disorder. Urticaria may occur in certain infectious diseases.

The characteristic symptom is the formation on the skin of roundish elevations or "hives." There may be an elevation of body temperature and partial loss of appetite. Small animals may act restless and show evidence of itching or pain. This symptom is very common in hogs. The eruption may last only a few hours or a few days, or, because of the animal's scratching or rubbing the part, the skin may become scabby and small pustules form.

An important preventive measure is to avoid the use of agents capable of irritating the skin and producing urticaria when treating parasitic skin diseases. It is very advisable to give the animal a saline cathartic (Epsom or Glauber's salts). The skin may be washed with cold water, or a weak water solution of permanganate of potassium.

ACNE, "SUMMER RASH."—In this skin disease the oil glands and hair follicles are inflamed and sometimes infected with pus germs. This results in skin eruptions varying in size from the point of a pin to about a quarter of an inch in diameter. This inflammation is most prominent during the warm weather.

The causes are local irritation to the skin from lying on filthy floors, sweating and irritation from the harness. According to some writers, pus germs are the only cause, the mechanical agents merely aiding in the production of the infection.

The face, side of the neck, shoulders, back and sides of the trunk and quarters are the usual seats of disease. The pimples or nodules may disappear within a few weeks, or persist throughout the warm season. The eruption may disappear without leaving scars, or suppuration occurs and small bald spots result.

The treatment consists in removing the cause of the disease and cleaning the skin with antiseptic washes. The surroundings of the animal must be kept clean and a good bed provided. If possible, the horse should be laid off from work as soon as the condition is noted. Washing the part with a weak water solution of permanganate of potassium may be practised daily. Fowler's solution of arsenic may be given. This may be given with the feed.

ECZEMA.—This is an inflammation of the vascular capillary bodies and the superficial layer of the skin. There may be marked inflammatory exudate, causing the surface of the skin to become excessively moist and more or less itching. Redness, vesicles and pustules may characterize the inflammation. In the chronic form the skin may become thickened and greatly changed in structure.

Eczematous inflammation of the skin may occur in all domestic animals, but it is most common in the dog. In the horse local eczema (scratches) is common.

The most frequent cause is external irritation. Accumulations of filth on the skin and continual wetting of the part are common causes. Mechanical causes are rubbing, pressure, the action of the sun's rays and chemical irritants. Internal causes, such as catarrhal diseases of the stomach and weakness and emaciation from disease, may act as direct or predisposing causes. Tender-skinned animals seem to be predisposed to the disease.

The symptoms vary in the different species of animals. In the horse the thin skin posterior to the fetlock and knee, in front of the hock and on the under side of the body is most commonly inflamed. Moisture and dirt seem to be the most common causes. Eczema may involve the skin covered by the mane and tail in animals that are not properly groomed and inclined to rub or scratch. Cattle may suffer from eczematous inflammations in the region of the forehead, back of neck and base of tail. A very common form of the disease involves the space between the toes. Sheep frequently suffer from inflammation of the skin over the fetlock region. The skin of animals having long fleeces, or heavy coats of hair that become wet at a time when there is no opportunity to dry out quickly, may become inflamed. Dogs are commonly affected by the acute and chronic forms of eczema. Eczema of swine is limited mostly to young hogs. It is rather rare, excepting in hogs that are pasturing on certain kinds of clover and rape, or on muck lands.

The inflammation is accompanied by a marked tenderness and itching, and the animal licks and scratches the part. This increases the extent of the skin lesions. The skin appears moist, later dirty, scabby and thickened. Cracks and pustules may form. Gangrene and sloughing of the skin may occur.

The treatment is both preventive and curative. Cases of eczema caused by filth and wetness can be prevented by giving the necessary attention to keeping the skin clean and not allowing animals access to muddy, filthy places. Keeping the bed clean and regulating the diet are important preventive measures. Before the inflammation can be successfully treated the cause must be removed.

In acute eczema it is advisable to protect the part against water, filth and air. Powders and ointments may be used during the early stages of the inflammation. Two parts boric acid, four parts flour, and one part tannic acid may be dusted over the moist surface. One part zinc oxide and twelve parts vaseline is a useful ointment. Scratching the part should be controlled in every case by muzzles, collars and bandages. Dirt and scales may be removed from the skin by washing with cotton soaked in lime water or linseed oil. The animal should receive laxative doses of Glauber's salts or oil every few days. A simple, easily digested ration should be fed. The following mixture may be applied in obstinate cases: oil of tar and soft soap, two parts each, and alcohol one part.

COMMON FEED RASHES.—This title includes inflammation of the skin caused by pasturing on buckwheat, certain clovers and rape, together with moisture and sunlight.

Green, flowering buckwheat is more dangerous as a feed for stock than is the grain or straw. Clovers and rape are not as dangerous a feed. The actual cause of the skin becoming inflamed is not known.

The skin in the regions of the face, ears, neck, lower surface of the body and limbs becomes red and covered with vesicles. Later, scabs and pus may form.

The treatment consists in changing the ration and keeping the animals out of the sun, or long grass and weeds for a few days. This is all the treatment required in most cases. It may be advisable to administer a physic. If pus and scabs form, the part should be cleansed daily with a one per cent water solution of permanganate of potassium.

HERPES (FUNGOUS SKIN DISEASE).—This is a contagious disease of the skin caused by thread fungi, Tricophyton tonsurans and epilans, which develop in the skin in localized areas, causing vesicles, scabs or scales to appear, and the loss of the hair over the part. This skin disease occurs in all domestic animals, but it is most commonly met with in cattle. It usually affects young cattle. It most commonly occurs in the region of the face and neck. Thick, bran-like crusts form over the scattered areas of the skin and the hair drops out or breaks off. The animals frequently rub the infected area.

Prompt treatment may prevent the spread of this disease in the herd. It may be checked by quarantining the infected animals and scrubbing the stalls, stanchions and walls with a disinfecting solution. Grooming the infected animal should be discontinued. This skin disease responds most readily to ointments. Flowers of sulfur one part and lard ten parts is commonly used by stockmen. Sulfur-iodide ointment, or tincture of iodine may be applied.

QUESTIONS

1. Give a general description of the skin.

2. Give the causes and treatment of falling of the hair.

3. What is urticaria? Give the treatment.

4. What is summer rash? Give the treatment.

5. What is "scratches"? Give the treatment.

6. What feeds produce rashes of the skin?

7. What fungus produces an inflammation of the skin in cattle? Give the treatment.