Each long is invested, upon its external surface, by an exceedingly delicate membrane, the pleura, which incloses the organ as far as its root, and is then returned upon the inner surface of the chest. The inner surface of the pleura is smooth, polished, and moistened by a fluid which favors the easy play of the surfaces, as the lungs alternately expand and collapse in movements of respiration.

In inflammation of this membrane or pleurisy, this lubricating fluid disappears, and the surfaces become roughened, hot, swollen, and painful as they come in contact and rub together with every inspiration. This condition rarely exists longer than twenty-four hours, and oftener a much shorter time; then follows an effusion into the affected side, the space being in some instances only partially filled, and in others the amount of fluid is of sufficient quantity to fill the cavity of the pleura, compressing the lung into a small, solid mass. In certain cases of acute pleurisy which pursue a favorable course, absorption of the liquid commences a few days after the accumulation has reached the maximum. Should the quantity remain stationary, or the diminution take place very slowly, after the elapse of two or three weeks, the disease becomes chronic.

Pleurisy is an unilateral disease, that is, it affects the pleura of one side only. While it may be associated with pneumonia (pleuro pneumonia), it does not tend to the development of that disease.

Causation

Acute pleurisy may be produced by contusions, especially if accompanied with fracture of the ribs, and penetrating wounds. It is remarkable, however, that severe injuries of the chest often occur without giving rise to this disease. Cold resulting from exposure, is the more fre. quent source of pleurisy. It may, however, be spontaneous, that is proceed from an unknown internal cause.

Symptoms

The attack is usually sudden. In a certain proportion of cases, however, some pain or soreness exists one, two, or three days before the development of acute inflammation. It is sometimes ushered in with a chill, as shown by shivering. Pain in the affected side attends the onset in a majority of cases, and is usually intense. It is sharp and cutting in character and is felt especially in the act of Inhaling. It increases during inspiration, often becoming so severe that the act is shortened and arrested before completed. This is due to the pain, caused by the rubbing together of the inflamed sides of the pleura as the lung expands. The respiration is consequently quickened, and the animal instinctively multiplies the acts to compensate for the want of a full inspiration.

Cough is usually present. The pain in coughing leads instinctively to efforts to repress it, and its character is termed suppressed.

Fever is coincident with the development of the Inflammation, varying in intensity in different cases.

The usual indications associated with fever are present; restlessness, thirst, pulse rapid, full, and bounding, nose hot and dry, tongue slightly coated, eyes watery, and wearing a pleading anxious look, the whites reddened and the lining of the lids deeper in color.

After a considerable amount of effusion has taken place, the symptoms are materially modified. The pain is notably lessened, the acts of coughing are less distressing, and the efforts at suppression not so apparent. The fever diminishes, and the other evidences of constitutional disturbance, in a manner disappear. The respirations continue, more or less hurried, their frequency now depending on the compression of the lung by fluid.

If a considerable amount of liquid is rapidly effused, the respirations are quickened; the animal suffers from a painful sense of the want of breath, and may be obliged to maintain a sitting posture, with fore legs spread widely apart. If the quantity is not large and the effusion has not taken place rapidly, less suffering will be noted while quiet, but exertion will cause panting and a sense of suffocation.

With a small quantity of effusion, the animal prefers, when lying down, to lie on the affected side, as in that position he is able to expand more fully the opposite lung. With a large quantity of fluid present, the breath-ing becomes more labored and abdominal as shown by the heaving action of the muscles of the flank. The limbs become dropsical, suffocation is threatened, and death may result from that cause.

Diagnosis

In the earlier stages some difficulty will be experienced in discriminating between the disease under consideration, and pneumonia. An examination of the chest by inspection, will show restrained movements, caused by the pain. Examination by the ear will determine the respiratory sound more or less weakened on the affected side, due to the fact that pain leads instinctively to a diminished use of the lung involved, while the action of the other lung is increased. No great importance can be attached to this sign alone, as in some attacks of pneumonia, severe pain may exist, and the same appearance be present. A pleural friction sound is a sound of grazing, rubbing, or grating, due to the movements, in opposite directions of the pleural surfaces with inspiration and expiration. The sound is more or less intense, dry, and appears to be near the ear, conveying'the idea of friction of roughened surfaces. If tills is distinctly present, its diagnostic significance is important, showing pleurisy exists.

The signs belonging to the second stage manifest themselves without much delay. Liquid effusion having taken place in sufficient quantity to be apparent, the diagnosis is easier.

The signs of an effusion are obtained by percussion, auscultation, and inspection. To determine by percussion, press the palm and fingers of the left hand firmly against the side of the chest, then tap lightly one finger with the second finger of the right hand, giving a sharp quick blow. If the sound given forth is dead and flat, it denotes an absence of air within the part of the chest percussed. On auscultation the respiratory sound is either suppressed or but feebly heard, unless the quantity of liquid is sufficient to compress the lung into a solid mass, then the sound is intensified, rude, and harsh, like that heard on placing the ear to the neck of the animal. If the quantity of liquid be large enough to distend the pleural sac, the depression between the ribs of affected side may be diminished and even swell out. This complete distension by liquid effusions is, however, exceptionally rare.

Prognosis

The prognosis in acute, uncomplicated cases of pleurisy, with but little effusion, is favorable, provided the constitution of the animal is not enfeebled. The presence of a large liquid effusion is a very unfavorable sign, and death may result from suffocation or exhaustion.

When recovery takes place from pleurisy, the roughened surfaces of the pleura come together and are united by adhesion of newly found tissue.

Treatment

The objects of treatment in acute pleurisy, differ in its different stages. The purposes in the first, are to arrest, if possible, the progress of the disease, to diminish its intensity, if it be not arrested, and to relieve suffering. The indications are essentially the same as in the earlier period of most acute inflammations.

The remedy of the first importance is opium in some form. It is invaluable not only for its palliative, but its curative action. By relieving pain, it diminishes the determination of blood to the inflamed parts. It also lessens the constitutional disturbance, and enables the system to tolerate better the local affection. Conjoined with the use of opium, remedies addressed to the circulation, may be employed. Aconite is preferred, because its sedative effect upon circulation is produced without depression. Blisters should not be applied in this stage. Cloths wrung out of hot water and bound around the chest will act as a palliative, and afford marked relief.

Opium and aconite are conveniently combined in the following mixture -

℞ . Morphiae Sulphatis gr. ij.

Tr. Aconiti Bad. gtt. xxv.

Aquas ℥ iij.

Ft. Mist. Sig. Dose one teaspoonful.

This should be given every three or five hours until the pain subsides and the animal is inclined to sleep.

While the pain continues, and the fever remains unabated, the sedative mixture should be persisted in. A mild purgative, in the form of syrup of buckthorn in tablespoonful doses may be added to the treatment, to aid in lessening the fever, and restraining the liquid effusion.

In the second stage after the pain and fever have subsided, the object of treatment is to promote absorption of the liquid. The kidneys may be stimulated to increased activity by the following -

℞ . Potass. Acet. ℥ iv.

Infos. Digitalis ℥ iv.

Aquaae ℥ ij.

Ft. Mist. Sig. Dose two teaspoonfuls every five or six hours.