In very favorable cases the effusion may disappear by the twentieth day of the disease. In many cases, however, it lasts with the false membranes for several weeks, and not infrequently for many months. Cases are recorded by Powell and others where the effusion remained of a sero-fibrinous character for eighteen months and two years. Flint mentions two cases where the effusion was permanent, having lasted for years. Wilson Fox67 thinks that there is but slight danger of the fluid becoming purulent from mere lapse of time unless the patient should have another fresh inflammatory attack. It must be noted, however, that such is not the case in children. Voyet68 says that simple pleurisy in infants is transformed into purulent pleurisy with facility and extreme rapidity—so much so that when with these a serous effusion is slowly absorbed there is great danger of suppuration taking place. M. Vertiac69 states that chronic serous pleurisy may not exist among children. In 13,000 sick children in eleven years Barthez did not have a single case. Pathological anatomy has demonstrated to us that this fluid in separating these neo-membranes on the parietal and pulmonary pleuræ increases their development. The plastic rugosities collect the fibrils of fibrin on their surface, in the same manner as they are found on the twigs in whipping the blood, and as the atheromatous deposits on the interior of blood-vessels favor the formation of emboli. These false membranes may cause a number of complications by surrounding the lung with a thick, inelastic shell. The collapse of one part of the lung diminishes necessarily the field of hæmatosis, and consequently causes a compensatory congestion of that lung, and even of the lung of the other side. This occurring in an individual predisposed to tuberculosis or in a condition to develop and cultivate the bacillus tuberculosis may start the disease. Formad70 maintains that pleurisy is a very frequent cause of pulmonary tuberculosis. These imperfectly organized embryonic membranes cause deformities of the thorax; they are good ground for the growth of pathological products, such as cancer or tubercle; their fragile capillary vessels are the principal cause of a most troublesome form of hemorrhagic pleurisy. (See [HEMORRHAGIC PLEURISY].) If the lung be compressed but a short time, it does not undergo irreparable injury, but if for a considerable time, the thickened organized membrane, with the effusion, causes a more or less considerable atelectasis, binding down the lung and preventing its expansion. The author holds that the effusion, after the fever has subsided, is, in itself, a foreign and troublesome element; for even with a medium effusion we are not exempt from unpleasant results.

67 Brit. Med. Journ., Dec., 1877.

68 Thèse de Paris, 1870.

69 Ibid., 1865.

70 Paper read before the Baltimore Clinical Society, February, 1883.

Although, in moderate effusions, there is no compression of the lung, yet there is necessarily collapse of it pari passu with the amount of fluid. This interferes with its retractive power—the aspiration force, as it has been called—by which the venous blood is drawn into the right side of the heart. T. B. Curtis of Boston calls attention to this very important fact, and shows that the result must be disturbance of circulation, with imperfect blood-supply to the heart, interrupted cardiac action, feeble arterial tension, together with venous repletion and stagnation. In consequence of this condition there is a diminution of the quantity of urine, and, as generally occurs where there is venous congestion, a small quantity of albumen, cyanosis, etc. Fraentzel, Traube, and Lichtheim attribute the venous stagnation, etc. to obstruction in the pulmonary circulation resulting from pressure exercised by the effusion. Curtis and Garland hold that these bad symptoms are not caused by pressure, but by the diminished pulmonic retractility which exercises the negative pressure of emptying the large venous trunks.

Such being the ill-effects of the retracted lungs, is it well to allow even a moderate amount of fluid to remain in the pleural sac after Nature has failed to remove it? Besides, the presence of liquid alone displaces the organs, especially the heart and lungs; adhesions form and keep them in an abnormal condition. The retracted lung, bound down by bands, becomes enfeebled, loses its suppleness, and is rendered rigid, seriously impairing respiration. There exist three factors—false membranes, adhesions,71 and interstitial pneumonia—which tend to seriously disable the lung and even to produce complete atelectasis pulmonum. We must bear in mind that there is some danger of the fluid becoming purulent, especially if a fresh inflammatory attack should occur. The less time a pleurisitic effusion lasts, the sooner the patient will be placed beyond the probability of these serious injuries to the process of hæmatosis. It is but right to give Nature an opportunity, assisted by iron, salines, diuretics, iodine, and even blisters, in cases of moderate effusion. The rapidity of Nature's work in many cases in removing large quantities of fluid here and elsewhere is wonderful. But if she does not act, we ought not to let our patient become feeble and depressed in his nutrition, or perhaps maimed for life, by not withdrawing the fluid. Sometimes the absorbents only half do their work of removing the fluid, and leave a quantity in the chest. Under these circumstances tonics, good diet, and change of air will complete the absorption.

71 According to Wilson Fox, the density of the adhesions and false membranes is determined within the first fortnight of the effusion.

The question arises, How long shall we wait for absorption? Test first, by exploratory puncture, the nature of the fluid: if it is fibro-serous day after day, try by the cyrtometer the size of chest and by percussion the exact amount of flatness. If there is no evidence of any decline of the effusion in two weeks, slowly withdraw some of the fluid. This will start the absorbents into activity, for the natural absorbing power of the pleura is diminished when it has been unduly stretched for some time. The layer of lymphatics subjacent to the pleura and communicating by stomata with the pulmonary lymphatics, together with the other absorbent vessels, appear to be unable to remove the fluid. We maintain that the pressure on the orifices of the lymphatics is often too great for absorption to take place, and that by removing the pressure we can start the absorbents into activity. Aspiration under these circumstances shortens the duration by several weeks and hastens convalescence. J. W. Hunt72 advises that we should wait two or three weeks before operating. Loomis73 says if the fluid remains stationary for one week, or is increasing when the cavity is half filled, we must operate. Barnes74 would only wait a few days if the chest is half full, to see if absorption will begin to remove it. When the chest is two-thirds full, he advises immediate surgical interference. Oxley75 advises a delay of three or four weeks before operating. Anstie's76 rule is to postpone operating for one month. T. Clifford Allbutt's77 general rule is, if an effusion rises above the angle of the scapula, and abides in that quantity or increases for two or three weeks in spite of adequate treatment, it must be drawn off, whether the patient be embarrassed by it or not. Bowditch78 says: "If the effusion does not subside under the medical treatment, and the symptoms have not lessened after two or at the utmost four weeks, I have, after long experience, been led to the following general rules for my own guidance: 1st. I never allow any time to elapse before performing thoracentesis after a decided and prominent dyspnoea appears, or if a sudden and very threatening orthopnoea occur, or if I find the chest has become full or more than half full of fluid in a perfectly latent manner during a month of illness. 2d. After there is dulness to the angle of the scapula, with the other rational and physical signs of pleuritic effusions, I tap within four weeks, even if the patient seems quite comfortable, if the line of dulness does not get lower and seem to subside under the treatment. I think fatal mistakes are made by delaying too long before tapping." The author prefers ordinarily to wait for the subsidence of the fever in acute cases, unless the effusion is in dangerous quantity. The practitioner must continually use the thermometer as well as observe physical phenomena and general symptoms. Cyrtometric tracings give very valuable indications as to the activity or non-activity of the absorbent vessels. After the fever subsides the fluid may be regarded as a foreign body doing harm to the two principal organic functions upon which the nutrition of the animal frame is dependent—respiration and circulation. It is from this standpoint that Dieulafoy79 advises, if absorption is slow or difficult after two or three days, that the fluid should be aspirated. The greatest success has been obtained in cases where the fluid has been present but a short time. The number of fatal cases is increased by delay of operation. Toussaint's cases show this:

4deaths in176casesoperateduponbetween1stand20thday.
6"80""""20thand60th"
1"7""""60thand120th"