Until the constancy of the microbian factor is demonstrated we must recognize the time honored doctrine, that pleurisy may be due to cold, exposure, over exertions, to traumatic injuries, blows, concussions, fractures, penetrating wounds, and to extension by contiguity from adjacent diseases.
Most commonly pleurisy is unilateral on the right side but is often on the left or on both sides.
Symptoms. There is the early symptom of shivering followed by a hot stage in which the limbs participate and partial sweats bedew the surface. There are first uneasy movements of the fore limbs with some lifting of the flanks and this discomfort increases until the patient is panting with pain and occasionally glancing round at his heaving flanks and even pawing as in colic. If the pleurisy is confined to one side the corresponding fore limb is often advanced before the other. The temperature is 102° and upward. The pulse is quick, hard and incompressible being usually compared to a jarred wire and beats from 48 to over 60 per minute. The breathing is highly characteristic. It is hurried, is carried on chiefly by the abdominal muscles to avoid the rubbing of the inflamed pleuræ on each other, and has the inspiration short and suddenly checked by an audible closure of the glottis while the expiration is slow and prolonged. This character of the breathing is well observed when the ear is placed against the false nostril. The laboring abdominal muscles stand out as a ridge from the outer angle of the ilium along the lower ends of the last ribs (pleuritic ridge). A tremor on this line is often noticeable in the early stages. It may also be felt by the hand laid on the costal region. The horse does not stand obstinately still as in pneumonia, but frequently moves as if seeking an easier posture. The short, hacking cough contrasts with the deep, rare cough of pneumonia. The expired air is not so hot, nor the mucous membrane of the nose so red as in the last named disease and there is no nasal discharge. A twitching of the muscles of the chest is sometimes seen and if the intercostal muscles are pressed upon, the animal winces and frequently grunts. This last symptom is likewise seen in rheumatic disease of the intercostal muscles (pleurodynia) but the absence of the fever, the cough, and other chest symptoms sufficiently distinguish this. Auscultation detects in the early stages in addition to a healthy respiratory murmur, a friction sound audible in inspiration only in short jerks near the close of the act and comparable to the rubbing of the palm of one hand over the other laid over the ear, but this is no longer heard when effusion of liquid has taken place into the pleuræ. Percussion in the early stages detects no change from the healthy chest resonance.
If not relieved in from twenty-four to thirty-six hours, a remarkable modification of the symptoms takes place indicating the occurrence of effusion. The violent symptoms are suddenly relieved. The quick catching breathing which is in many cases accompanied by a grunt, becomes easy and though fuller than natural is comparatively regular. In particular the inspiration is free and full and comparatively painless, the sudden check and the grunt by which it was arrested having alike disappeared. The tension of the abdominal muscles and the tucked up appearance of the flanks give way; the pulse acquires a softer character, the haggard pinched countenance is relaxed, and a general appearance of comfort and even liveliness prevades the animal. This temporary improvement is often so great that the horse will take to feeding as if he had all at once recovered.
The apparent recovery is, however, only transient. Soon the pulse becomes more frequent and loses its fulness, the breathing is more laborious and attended with a characteristic lifting of the flanks and loins, the nostrils are widely dilated, the limbs outstretched and the elbows outturned, the eyes stare and project and the countenance has a haggard appearance indicating threatened suffocation. Partial sweats may break out on the surface, due to the state of nervous excitement and general relaxation and supplementing in some degree the impaired exhalation from the lungs. Auscultation over the lower region of the chest shows a complete absence of the respiratory murmur, rising to the same level precisely at all points. Percussion elicits no resonance on the same region. If the effusion has taken place slowly or existed for some time, the dulness and absence of sound will usually indicate that the liquid rises to the same level on both sides. So thin and permeable is the posterior mediastinum in its lower part that unless thickly coated by new solid exudations, the effusion readily passes through it and rises to the same height on both sides. If gas as well as liquid is produced in the pleural sac a gurgling or splashing sound may be heard on auscultation, and occasionally, after rising or other change of position, a metallic tinkling, due to droppings from the shreds of false membranes above into the fluid below.
As the disease proceeds dropsical effusions are observed beneath the skin of the breast and abdomen, a mucous rattle is heard in the trachea, the nose, ears and limbs become cold, the pulse increases in rapidity and weakness, shows the distinct anæmic tremor or thrill, and becomes rapidly imperceptible; the horse moves unsteadily and often falls suddenly dead.
This early fatality is, however, only seen in the worst cases. In those about to terminate favorably improvement is shown usually about the fourth day. The lifting of the flanks and loins becomes moderated, the ribs move more freely, the grunt ceases, the pulse is fuller, softer and less frequent, and auscultation and percussion show a steady decrease in the effusion. Appetite meanwhile returns, the horse moves more freely, lies down for a length of time in succession, and convalescence lasts from two to three weeks.
In the less fortunate cases structural changes more or less permanent, keep up symptoms of illness for a variable length of time. Sometimes after the liquid effusion has been absorbed the lung remains attached to the side of the chest by newly formed tissue (false membrane) and while this is undergoing a drying and organizing process, it gives rise to a leathery, creaking sound heard on auscultation and easily mistaken for crepitation. Sometimes an abscess forms on the surface of the pleura or in the newly organized false membrane, and either bursts into the pleural sac (empyema) where it serves to increase and sustain the irritation, or it makes its way through the intercostal spaces and is discharged externally. In this last case its advance toward the surface is heralded by an extensive inflammatory infiltration and pasty swelling much more tender to the touch than the dropsical swelling already referred to. Another condition is that in which false membranes of considerable thickness invest a lung and, following the law of all fibrous structures in process of organization, they contract and cause a compression and partial collapse of the contained lung tissue. A flattening of the corresponding side of the chest and a muffled and almost inaudible respiratory murmur is the result of this condition. In some measure these symptoms are present during convalescence in all cases of pleurisy since the lung never expands to its full size till some time after apparent recovery, but it is only when the organ is invested with false membrane that the symptoms are very apparent.
In all such cases of prolonged pleurisy from protracted structural change there is continued illness without the violent symptoms by which the acute form of the disease is manifested. The acute suffering, the restlessness, the grunt, and even the catching breathing may be absent; the temperature may be almost reduced to the healthy standard, the pulse small and tolerably soft, the appetite considerably improved and the different secretions tolerably normal; yet the pinching of the intercostal spaces causes sharp pain, and measurement, auscultation and percussion testify to the persistence of disease. The animal is hidebound, unthrifty and unequal to any exertion. The cough is weak and painful and sometimes accompanied by a grunt.
Besides the changes connected with exudation and effusion, and organization or suppuration in the exuded products, gangrene sometimes results. A case of this kind is related by Percivall.