PLEURISY, or PLEURITIS (Gr. srXeiipc =ribs)  , inflammation of the pleura, caused by invasion by certain specific micro-organisms . (See RESPIRATORY SYSTEM: Pathology.) Secondary pleurisies may occur from extension of inflammation from neighbouring organs . The morbid changes which the pleura undergoes when inflamed consist of three chief conditions or stages of progress . (I) Inflammatory congestion and infiltration of the pleura, which may spread to the tissues of the lung on the one hand, and to those of the chest wall on the other . (2) Exudation of lymph on the pleural surfaces . This lymph is of variable consistence, some-times composed of thin and easily separated pellicles, or of extensive thick masses or strata, or again showing itself in the form of a tough membrane . It is of greyish-yellow colour, and microscopically consists mainly of coagulated fibrin along with epithelial cells and red and white blood corpuscles . Its presence causes roughening of the two pleural surfaces, which, slightly separated in health, may now be brought into contact by bands of lymph extending between them . These bands may break up or may become organized by the development of new blood vessels, and adhering permanently may obliterate throughout a greater or less space the pleural sac, and interfere to some extent with the free play of the lungs . (3) Effusion of fluid into the pleural cavity . This fluid may vary in its characters . The chief varieties of pleurisy are classified according to the variety of the effusion, should effusion take place .

(1) Some pleurisies do not reach the

stage of effusion, the inflammation terminating in the exudation of lymph . This is termed dry pleurisy . (2) Fibrinous or plastic pleurisy . In this variety the pleura is covered by a thick layer of granular, fibrinous material . Fibrinous pleurisy is usually secondary to acute diseases of the lung such as pneumonia, cancer, abscess or tuberculosis . (3) Sero-fibrinous pleurisy . This is the most common variety, and produces the condition commonly known as pleurisy with effusion . The amount may vary from analmost inappreciable quantity to a gallon or more . When large in quantity it may fill to distension the pleural sac, bulge out the thoracic wall- externally, and compress the Iung, which may in such cases have all its air displaced and be reduced to a mere fraction of its natural bulk . Other organs, such as the heart and liver, may in consequence of the presence of the fluid be shifted away from their normal positicn . In favourable cases the fluid is absorbed more or Iess completely and the pleural surfaces again may unite by adhesions; or, all traces of inflammatory products having disappeared, the pleura may be restored to its normal condition . When the fluid is not speedily absorbed it may remain long in the cavity and compress the lung to such a degree as to render it incapable of re-expansion as the effusion passes slowly away .

The consequence is that the chest wall falls in, the ribs become approximated, the

shoulder is lowered, the spine becomes curved and internal organs permanently displaced, while the affected side scarcely moves in respiration . Sometimes the unabsorbed fluid becomes purulent, and an empyema is the result . The symptoms of pleurisy vary; the onset is sometimes obscure but usually well marked . It may be ushered in by rigors, fever and a sharp pain in the side, especially on breathing . Pain is felt in the side or breast, of a severe cutting character, referred usually to the neighbourhood of the nipple, but it may be also at some distance from the affected part, such as through the middle of the body or in the abdominal or iliac regions . On auscultation the physician recognizes sooner or later " friction," a superficial rough rubbing sound, occurring only with the respiratory acts and ceasing when the breath is held . It is due to the coming together during respiration of the two pleural surfaces which are roughened by the exuded lymph . The pain is greatest at the outset, and tends to abate as the effusion takes place . A dry cough is almost always present, which is particularly distressing owing to the increased pain the effort excites . At the outset there may be dyspnoea, due to fever and pain; later it may result from compression of the lung . On physical examination of the chest the following are among the chief points observed: (I) On inspection there is more or less bulging of the side affected, should effusion be present, obliteration of the intercostal spaces, and sometimes elevation of the shoulder . (2) On palpation with the hand applied to the side there is diminished expansion of one-half of the thorax, and the normal vocal fremitus is abolished .

Should the effusion be on the right side and copious, the liver may be felt to have been pushed downwards, and the heart somewhat displaced to the

left; while if the effusion be on the left side the heart is displaced to the right . (3) On percussion there is absolute dullness over the seat of the effusion . If the fluid does not fill the pleural sac the floating lung may yield a hyper-resonant note . (4) On auscultation the natural breath sound is inaudible over the effusion . Should the latter be only partial the breathing is clear and somewhat harsh, with or without friction, and the voice sound is aegophonic . Posteriorly there may be heard tubular breathing with aegophony . These various physical signs render it impossible to mistake the disease for other maladies the symptoms of which may bear a resemblance to it, such as pleurodynia . The absorption or removal of the fluid is marked by the disappearance or diminution of the above-mentioned physical signs, except that of percussion dullness, which may last a long time, and is probably due in part to the thickened pleura . Friction may again be heard as the fluid passes away and the two pleural surfaces come together . The displaced organs are restored to their position, and the compressed lung re-expanded . Frequently this expansion is only partial . In most instances the termination is favourable, the acute symptoms subsiding and the fluid (if not drawn off) becoming absorbed, sometimes after reaccumulation .

On the other hand it may remain long without undergoing much

change, and thus a condition of chronic pleurisy becomes established . Pleurisy may exist in a latent form, the patient going.about for weeks with a large accumulation of fluid in his thorax, the ordinary acute symptoms never having been present in any Zealand and Tasmania received it in 1864, but it was eradicated in both countries by the sanitary measures adopted . It was carried to Asia Minor, and made its presence felt at Damascus . It prevails in various parts of China, India, Africa and Australia, and until quite recently it existed in every country in Europe, except Scandinavia, Holland, Spain and Portugal . In Great Britain cases occurred in 1897 . Symptoms:—The malady lasts from two to three weeks to as many months, the chief symptoms being fever, diminished appetite, a short cough of a peculiar and pathognomonic character, with qnickened breathing and pulse, and physical indications of lung and chest disease . Towards the end there is great debility and emaciation, death generally ensuing after hectic fever has set in . Complete recovery is rare . The pathological changes are generally limited to the chest and its contents, and consist in a peculiar marbled-like appearance of the lungs on section, and fibrinous deposits on the pleural membrane, with oftentimes great effusion into the cavity of the thorax . Willems of Hasselt (Belgium) in 1852 introduced and practised inoculation as a protective measure for this scourge, employing for this purpose the lymph obtained from a diseased lung . Since that time inoculation has been extensively resorted to, not only in Europe, but also in Australia and South Africa, and its protective value has been generally recognized . When properly performed, and when certain precautions are adopted, it would appear to confer temporary immunity from the disease .

The usual seat of inoculation is the extremity of the tail, the

virus being introduced beneath the skin by means of a syringe or a worsted thread impregnated with the lymph . Protection against infection can also be secured by subcutaneous or intravenous injection of a culture of Arloing's pneumo-bacillus on Martin's bouillon, and by intravenous injection of the lymph from a diseased lung, or from a subcutaneous lesion produced in a calf by previous inoculation .