4. What is "moonblindness"? Give the symptoms.

5. Describe the symptoms of infectious ophthalmia of ruminants and the treatment.

CHAPTER XIII

GENERAL DISEASES OF THE LOCOMOTORY APPARATUS

GENERAL DISCUSSION.--The movements of the different parts of the animal body depend on the union of the bones that form the skeleton (Fig. 28), and mode of insertion of the muscles. The bones meet and form _joints_ or _articulations_. These are divided into three cla.s.ses: _movable_, _mixed_ and _immovable_. Nearly all of the articulations in the extremities belong to the movable cla.s.s. The articulations between the bodies of the vertebrae belong to the mixed, and those between the flat bones of the head to the immovable cla.s.s.

[Ill.u.s.tration: FIG. 28.--Skeleton of horse.]

The bony surfaces that meet and form the different types of articulations are held together by ligaments (Fig. 29). Sometimes the ligament is placed between the bony surfaces, but usually it is attached to the margins of the articular surfaces that it unites. The _immovable cla.s.s_ possesses fibrous-like ligaments that are placed between the margins of the flat bones that form the articulation. The _mixed articulations_ are united by a fibro-cartilaginous pad that is firmly attached to the articular faces of the bones, and by peripheral ligaments that may be flat or formed by scattered fibres. All _movable articulations_ are formed by bony surfaces encrusted with a thin cartilaginous layer that makes them perfectly smooth, ligaments and complimentary cartilages. Sometimes the bony surfaces do not fit each other, and we find between them _fibro-cartilages_ that complete the articulation by adapting the articular surfaces to each other. _Round_ or _flat ligaments_ may extend from one articular surface to the other, and attached to the margins of the articulation are _membranous, flat_ or _round ligaments_. Muscles and tendons that cross the articulations should be included among the structures binding them together.

[Ill.u.s.tration: FIG. 29.--Photograph of model of stifle joint, showing: ligaments; complementary cartilages; femur; and tibia.]

Movable joints possess a _synovial membrane_. This membrane lines the structures that enclose the articulation and secretes a fluid, _the synovia_, that lubricates the surfaces.

_The muscles_ are the contractile organs that move the body. The movement of the different parts of the body is rendered possible through the manner in which the skeletal muscles are inserted into the long bones, by which the lever motion is possible. A muscle originating on one bone and terminating on another either moves both bones toward each other or, if one attachment is fixed, the movable is drawn toward the fixed part.

We may cla.s.s muscles as _striated_ or _voluntary_ and _unstriated_ or _involuntary._ A third cla.s.s, _mixed,_ is represented by the heart muscle.

The striated is represented by the skeletal muscles, and the unstriated by the thin muscular layers that form part of the wall of the stomach, intestines, bladder and other hollow organs.

RHEUMATISM.--This is an inflammation of the tissues that form the locomotory apparatus. The effect of cold on the muscles and tendons is an important factor in its production. It differs from other inflammations by shifting from one part to another. It is termed _muscular rheumatism_ when it affects the muscles, tendons and fascia, and _articular rheumatism_ when it involves the articulations. A second cla.s.sification, _acute_ and _chronic,_ depends on the character of the inflammation. The muscular form is common in horses, dogs and hogs, while the articular form more commonly affects cattle.

_The following causes_ may be considered. Animals that are exposed to cold, wet, changeable weather, or kept in cold, damp, draughty quarters frequently suffer from rheumatism. Under such conditions it is very probable that imperfect metabolism of body tissue occurs, and certain toxic products that are capable of irritating the muscles and articulations form.

Clinical symptoms, and the presence of bacteria in the inflamed tissue indicate that bacteria and their toxins play an important part in the development of articular rheumatism. Heredity is said to be an important predisposing factor. One attack always predisposes the animal to a second.

_The symptoms vary_ according to the severity of the attack. Local rheumatism is not accompanied by serious symptoms. The regions most commonly involved in local, muscular rheumatism are the shoulder, neck and back. The joints affected in the articular form are the knee, fetlock, hip, elbow and shoulder. The attack is usually sudden and accompanied by fever, more or less loss of appet.i.te and soreness. Loss of control over the movement of the hind parts or walking on the knees may occur in the smaller animals. The larger animals show a slight or severe lameness. The affected muscle or articulation may be swollen, hot and tender. Pressing on the part with the hand or forcing the animal to move about may cause severe pain.

Weakness and emaciation may occur in generalized and articular rheumatism, especially if suppuration takes place in the affected joint.

_The prognosis_ is more favorable in muscular rheumatism than in the articular form. Both forms may become chronic. It is frequently advisable to destroy animals suffering from the articular form because of their emaciated, weakened condition and the deformed condition of the joints.

_The preventive treatment_ consists in avoiding conditions favorable to the production of rheumatism. In ventilating the stable we should avoid draughts. Practical experience indicates that allowing a horse to stand in a draught after it has been warmed up by exercise is a very common source of muscular rheumatism and is especially to be avoided. Young hogs and sows that are thin are very p.r.o.ne to rheumatism when given wet, draughty sleeping quarters. Houses having dirt or loose board floors are very often draughty. Concrete floors when wet and not properly bedded with straw are objectionable. Although we do not fully understand the causative factors, we can take advantage of the knowledge we have gained from practical experience, and avoid keeping animals under conditions that are favorable for the production of the disease. It is almost useless to treat rheumatism unless the conditions under which it occurred are corrected.

_The treatment_ is both local and internal. The local treatment consists in applying a mild liniment to the part, together with ma.s.sage. If the part is tender and painful, hot applications may be used. Spirits of camphor ten parts and turpentine two parts, applied daily, are useful in relieving the soreness of rheumatic muscles. Salicylate of soda two ounces, fluid extract of gentian one ounce, and sufficient water to make an eight-ounce mixture may be given internally three times daily after feeding. Of the above mixture horses and cattle may be given one-half ounce and sheep and swine from one to two drachms. The treatment should be continued for a period of from eight to ten days or longer. It may be repeated in from one to two weeks.

[Ill.u.s.tration: FIG. 30.--Atrophy of the muscles of the thigh resulting from an attack of azoturia.]

Iodide of pota.s.sium is very useful in the treatment of chronic articular rheumatism. A very light diet should be fed and the animal given as complete rest as possible. An occasional physic should be given.

AZOTURIA, HAEMOGLOBINURIA.--This is a disease of solipeds affecting the muscles of the quarters. The affected muscles become swollen, hard and paralyzed. The disease follows a short rest, and rarely occurs when the animal is running in pasture or idle for a long period. Animals that are fat or rapidly putting on fat are predisposed to it. Animals that have had one attack are predisposed to a second.

_The cause_ of this disease is not positively known. The German veterinarians attribute it to irritation of the muscles by cold, and cla.s.sify azoturia as a rheumatic disorder. The conditions preceding the attack are not in favor of this theory, and cold can not be considered an important causative factor. The most acceptable is the auto-poisoning theory advanced by Dr. Law.

Azoturia is common in the country where feed is abundant and wrong methods of feeding horses are commonly practised. It is a very common practice to feed horses accustomed to hard work the same ration when idle for a few days as when working. The blood of horses cared for in this way may become abnormally rich in alb.u.minoids. The suddenness of the attack, occurring shortly after the animal is given exercise, indicates auto-poisoning. This may be due to the blood in the portal vessels and the liver capillaries, charged with nutritious and waste products from the overfed animal's intestines, being suddenly thrown into the general circulation by a more active circulation of the blood brought on by exercise.

_The symptoms_ of disease are manifested shortly after the animal is moved out of the stall and given exercise. When the animal is first exercised it is usually in high spirits. After travelling a short distance it is noticed to sweat more freely than ordinarily, breathe rapidly, lag and go lame, usually in the hind limbs. It trembles, shows evidence of suffering severe pain by turning its head and looking around toward the flanks, knuckles over in the hind pasterns, and may fall down and be unable to get up. The affected muscles appear to be swollen and feel unusually firm when pressed upon with the hand. If the horse does not go down recovery may occur within a few hours, and we are able to move the horse to the stable. Dark brown urine may be pa.s.sed. At other times, the animal lies in a natural position, possesses a good appet.i.te, but can not stand. In the severe form, it is restless and shows marked nervous symptoms.

_The prognosis_ is unfavorable in the severe form. When nervous symptoms are absent recovery usually occurs in from two to ten days. Complications are common. More or less atrophy of the muscles of the quarters may result (Fig. 30).

_The preventive treatment_ consists in avoiding conditions that may favor the production of the disease. More attention should be given the feeding and care of work animals. If it is not possible to permit horses that are worked to exercise in a lot or pasture when idle, the ration should be reduced and roots, chopped, or soft feed given.

Careful nursing is an important part of the _treatment_. As soon as the horse shows evidence of an attack, it should be stopped and allowed to stand until sufficiently recovered to be moved. If paralysis occurs, we should make it as comfortable as possible and arrange to move it to a comfortable, warm, well-bedded stall. It may be advisable to place the animal in slings. This is not advisable in the serious form of the disease because of the extent of the paralysis and the nervous symptoms. A very light diet, bran mashes, chopped hay or green feed, should be fed during the convalescent period and for several days after complete recovery has occurred.

The following lines of _medicinal treatment_ may be recommended. We should endeavor to stimulate the elimination of the waste products from the body by way of the kidneys, intestines and skin. This may be accomplished by administering saline cathartics, covering the body with blankets, encouraging the animal to drink plenty of water and feeding soft feeds.

Glauber's salts may be given as a drench, or eserine may be given hypodermically. Sedatives such as chloral hydrate may be used to quiet the animal.

QUESTIONS

1. Give a general description of the locomotory apparatus.

2. Give the causes of rheumatism; describe the treatment.

3. What is azoturia? Give the cause of this disease.

CHAPTER XIV

STRUCTURE OF THE LIMBS OF THE HORSE

GENERAL DISCUSSION.--Each limb is formed by a column of bones that rest upon one another, forming more or less open angles. The bones of the column meet and form articulations that are held together by ligaments, and attached to their faces, borders and extremities are muscles and tendons.

In the superior portion of the limb the muscles are heavy, tapering inferiorly, and terminating in the region of the foot in long tendons. Each limb is divided into four regions. The regions of the _fore-limb_ are the shoulder, arm, forearm and forefoot. In the _hind limb_ are the regions of the pelvis, haunch, thigh, leg and hind-foot. The feet in turn are divided into three sub-regions each. The _forefoot_ is formed by the knee, cannon and toe, and the _hindfoot_ by the hock, cannon and toe.

THE SHOULDER BONE OR SCAPULA is flat and triangular in shape. It is attached to the trunk by heavy muscles, one of which, together with its fellow on the opposite side, may be compared to a great, muscular sling that supports about two-thirds of the body weight. Attached to the internal and external faces of the scapula are heavy muscles that pa.s.s over the shoulder-joint, and become attached to the arm bone through the insertion of their muscular fibres or by a short tendon.

THE ARMBONE OR HUMERUS belongs to the cla.s.s of long bones. Its superior extremity forms a flattened head that fits rather imperfectly into a shallow cavity in the humeral angle of the scapula. The inferior extremity resembles a portion of a cylinder in shape, and fits into shallow depressions in the superior extremity of the princ.i.p.al bone of the forearm.

The muscles here are divided into two regions, anterior and posterior brachial. The most of these muscles originate on the posterior border and inferior extremity of the shoulder bone, and terminate inferiorly on the superior extremities of the princ.i.p.al and second or rudimentary bone of the forearm. The posterior brachial muscles are heavy and powerful. They are sometimes termed elbow muscles, because they are attached to the point of the elbow.

THE REGION OF THE FOREARM is formed by two bones, the _radius_ and _ulna_.

The radius is the princ.i.p.al bone and is cla.s.sed among the long bones. The ulna is an elongated flat bone. It is attached to the external portion of the posterior face of the radius and extends above the superior extremity of this bone to form the point of the elbow. The radius articulates with the upper row of knee bones. The muscles of this region, the antibrachial, are divided into two sub-regions, anterior and posterior. They originate superiorly from the lower extremity of the arm bone and the superior extremities of the bones of the forearm, and terminate toward the lower extremity of the region in tendons that become attached to the bones of the knee, cannon and digit.

THE KNEE OR CARPAL region is formed by seven short bones that are arranged in two rows. They form a series of articulations. These are the articulations between the two rows, between the bones of each row, and between the upper and lower rows and the neighboring regions. Nearly all the motion takes place in the articulation between the upper row and the princ.i.p.al bone of the forearm.

THE CANNON OR METACARPAL region is formed by three bones. These are the princ.i.p.al metacarpal or cannon bone, and the rudimentary metacarpal or splint bones. The latter are attached to the margins of the posterior face of the cannon bone. The superior extremities of these bones articulate with the lower row of carpal bones. The convex extremity of the cannon bone meets shallow depressions in the superior extremity of the first digital bone. This is termed the fetlock joint. The anterior and posterior faces of this region are travelled by the long tendons belonging to the extensor and flexor muscles of the digit.

THE DIGIT OR TOE is formed by six bones, three of which are termed accessory or sesamoids. The digital bones may be given numerical names.

THE APPROXIMAL OR THIRD DIGITAL BONE is the shortest long bone in the body.

The two shallow articular cavities belonging to the superior extremity are completed posteriorly by the two sesamoid bones. The inferior extremity is smaller than the superior and resembles the inferior extremity of the cannon bone in shape, excepting that it shows a middle groove. The anterior and posterior faces are travelled by the tendons of the digital muscles.