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.
CHAPTER XII
DISEASES OF THE EYE
GENERAL DISCUSSION.--_The eye_ is situated in the orbital cavity, to which it is attached by muscles that rotate it in different directions. The _orbit_ is lined by fibro-fatty tissues that form a cushion for the eye.
Anteriorly it is protected by the _eyelids_, and in birds by a third eyelid that corresponds to the membrana nictitans of quadrupeds. The _lachrymal gland_ which secretes the tears keeps the above parts moist.
_The eye_ is the essential organ of vision. It is formed by a spherical shell which encloses fluid or semisolid parts. The shell is anteriorly made up of a transparent convex membrane, the cornea, while the remainder of its wall is formed by three opaque layers or tunics.
The external tunic is the _sclerotic_. It is a white, solid membrane, forming about four-fifths of the external shell. Its external face is related to the muscles and fatty cushion. It receives posteriorly, a little lower than its middle portion, the insertion of the _optic nerve_, which passes through the shell and spreads out to form a very thin membrane, the retina or internal coat.
_The retina_ lines about two-thirds of the posterior portion of the shell of the eye. It is made up of seven layers. The essential layer is named from its appearance, rods and cones.
The middle coat is the _choroid_. This is a dark, pigmented, vascular and muscular membrane. The posterior portion is in contact with the retina.
Anteriorly it forms the ciliary processes and the iris.
_The media_ of the eye are the crystalline lens, vitreous and aqueous humors. The _crystalline lens_ is a transparent, biconvex body sustained by the ciliary processes. The _vitreous humor_ is a transparent jelly-like substance that fills all the cavity of the eye posterior to the lens. The _aqueous humor_ is a liquid, contained in the anterior and posterior chambers of the eye in front of the lens. This fluid separates the iris from the front of the lens.
EXAMINATION OF THE EYE.--In examining and treating the eye we should avoid rough and hasty manipulation. The animal should be approached slowly. It is best for the attendant who is familiar with the animal to hold it for the examiner. It is advisable on approaching the animal to stroke its face, and in the horse to brush its foretop away. The hand should be carried slowly to the front of the eye, and the lids separated with the fingers and thumb if we wish to obtain a better view of the cornea. In cattle the best view of these parts can be obtained by taking hold of the nose and lifting the head. It is impossible to make a satisfactory examination of the eye outside of the stable where the light is coming from all directions. The most satisfactory conditions under which a general examination can be made is to stand the animal facing a transom, window or open door. We may then look directly into the eye and note the condition of the different refracting media.
The lens should appear transparent and free from scars. The aqueous humor free from any cloudiness or precipitate. Both pupillary openings should be the same size, and not too small or too large in the bright light. As we look through the pupillary openings, both the lens and the vitreous humor should refract the light properly and not appear white or greenish-white in color. The color of the iris should be noted. If it lacks lustre or appears dull, this may indicate an inflammation. In periodic ophthalmia in horses the iris loses its lustre and becomes a rusty-brown color. It is very important to note this change in the appearance of the iris. We should note, in addition, the expression of the animal's face, the position of the ears and eyelids and manner of the walk. Horses that have defective sight may show a deep wrinkle in the upper eyelid when startled or looking directly at an object. Animals that are blind hold the ears in a characteristic position, and may stumble and walk over, or run into objects unless stopped. The ophthalmoscope is a very useful instrument for determining the condition of the different structures of the eyes, when in the hands of persons who are trained in its use.
CONJUNCTIVITIS.--This is an inflammation of the mucous membrane lining the eyelids and covering the eyeball. The two forms of conjunctivitis common in domestic animals are the _catarrhal_ and _purulent_.
_The symptoms differ_ in the two forms of conjunctivitis. They may be distinguished from each other by the difference in the character of the inflammatory discharge. In the catarrhal form, there is a discharge of tears and the lids are held more or less closed. The mucous membrane is usually brick red in color and swollen. A little later the discharge becomes heavier and adheres more to the margins of the lids. The lids continue tender and the inflammation painful. The surface of the cornea may appear white and the blood-vessels prominent, but it is only in the severe cases that inflammation of this portion of the eye occurs. In such cases an elevation in body temperature may occur. This is especially true of purulent conjunctivitis when primarily caused by an infectious agent. In the purulent form the discharge is heavy and pus-like.
_The treatment_ is both preventive and curative. The first object must be to remove the cause. Irritating gases resulting from stable filth should be remedied by correcting the unsanitary conditions in the stable. Conditions favoring injury to the eye from foreign bodies, such as chaff and a careless attendant, should be corrected. Animals suffering from the infectious or purulent form of inflammation should be separated from the other animals. Foreign bodies should be removed promptly before they have had an opportunity to set up a serious inflammation. It is necessary to confine the animal in some way before attempting to do this. Horses should be twitched, cattle held by the nose, and the head of a small animal held firmly with the hands. It may be necessary to cocainize the eye before the operator can remove the foreign object with absorbent cotton or with forceps.
In case of injuries and irritation to the lids by foreign bodies, the eye may be flooded with a three per cent water solution of boric acid twice daily, or as often as necessary. Such washes or lotions may be applied with a small piece of absorbent cotton, using a fresh piece each time the eye is dressed. A medicine dropper may also be used. A lotion containing silver nitrate two to four grains and distilled water one ounce, is useful in combating the inflammation. This may be applied twice daily. Irritating lotions should be avoided, if possible, in the treatment of eye diseases of horses, because of the danger of making the animal disagreeable to handle.
Boric acid may be dusted over the ball of the eye of cattle with a powder blower.
PERIODIC OPHTHALMIA, "MOONBLINDNESS."--This is a periodic inflammation of one or both eyes of the horse. The internal structures of the eye are involved by the inflammation, but it may appear as a conjunctivitis.
_The cause_ of this disease is not well understood. Certain local conditions seem to favor its development. Undrained land, a humid climate, the feeding of a one-sided ration or one that does not maintain the vitality of the animal, and severe work seem to produce it. Heredity must be accepted as a prominent accessory cause. A number of different bacteria have been mentioned as causative factors for this disease.
_The symptoms_ at the very beginning indicate a general inflammation of the eye. The eyelids are swollen, there is an abundant secretion of tears, the eyeball is retracted and the lids are held more or less closed. As the inflammation progresses, the cornea becomes milky in appearance and the aqueous humor may show a precipitate toward the bottom of the anterior chamber. The pupil is usually contracted and dilates slowly when the animal is moved into the light. The acute inflammation gradually subsides, and about the tenth to the fourteenth day the lids and cornea may appear normal.
The periods between these acute attacks of ophthalmia may vary from a few weeks to several months. Severe work, debility and the character of the ration influence their frequency. It is not uncommon for animals that have been given a rest to suffer from a second attack on being put to work. The attendant may observe a hazy or whitish condition of the margin of the cornea. The upper lid may show an abrupt bend of its margin and a deep wrinkle. The color of the iris appears to have lost its lustre, and the aqueous humor and lens may be cloudy. After a variable number of attacks glaucoma or cataract develops.
_The history_ of the case will enable the attendant to recognize this form of ophthalmia.
_Treatment_ is unsatisfactory. Preventive measures consist in avoiding conditions favorable to the production of the disease. This should be practised so far as possible. At the time the attack occurs, the animal should be given a cathartic. One pound of Glauber's salts in a drench is to be preferred. Rest in a darkened stall is indicated. An eye lotion containing three grains of silver nitrate in one ounce of distilled water should be applied to the eye three times daily. A water solution of atropine or eserine should be used for the purpose of relieving the symptoms of iritis or glaucoma. A very light diet should be fed.
INFECTIOUS OPHTHALMIA OF RUMINANTS.--This occurs as an acute inflammation of the eyelids and cornea. The disease is highly infectious, affecting all of the susceptible animals in the herd. It commonly occurs during the late summer and fall.
_The symptoms appear_ suddenly. The animal is feverish, the eyes closed and the cheeks are wet with tears. The cornea becomes clouded, white and opaque. In severe cases, the blood-vessels around the margin of the cornea become prominent, and ulcers form on its surface. The animal's appetite is impaired or lost. There is loss of flesh and temporary blindness. The blindness in one or both eyes may persist for a period of from two weeks to several months. Permanent blindness is comparatively rare.
_The preventive treatment_ consists in practising the necessary precautions against the introduction of the disease into the herd, and in carefully quarantining the first cases of the disease that appear. The affected animal should be given a darkened stall, and fed a very light ration until the acute inflammation has subsided. From one to one and one-half pounds of Glauber's salts should be given. The _local treatment_ consists in the application of antiseptic lotions or powders to the eye. Equal parts of boric acid and calomel, dusted into the eye twice daily with a powder blower, is a very effective treatment.
QUESTIONS
1. Name the different structures that form the shell of the eye; name and describe the different media of the eye.
2. Give the general method of examining the eyes of horses.
3. What is conjunctivitis? Give causes and treatment.