Contraction, even when arising from general pleurisy, may affect only one portion of the chest; the upper portion may be thus modified, while the lower remains either absolutely dilated, or, at all events relatively so, as contrasted with the sunken portion. Thus, after partial resorption of the effused fluid, an adhesion of the lamellae of the fibrous exudation may take place, while inferiorly they are separated from one another by the effusion stagnating between them. Partial contractions of the thorax are most commonly the result of partial and circumscribed pleurisies, as we see from the depression of the thorax in the neighborhood of the clavicles, in consequence of pleurisy being associated with pulmonary tuberculosis around the apices of the lungs; and from the contraction of the lower part of the thorax, in consequence of pleurisies about their base.

The fibrous exudation, and especially its parietal lamella, sometimes undergoes ossification; this change occasionally occurs before, but more generally after, the complete absorption of the serous effusion. The deposition of osseous matter, for the most part, occurs in the thickest portions of the exudation in the form of compact nodulated strings and plates. There are rare cases in which thin osseous plates are formed over the whole pseudo-membranous pleural cone, excepting the thin layer investing the lung, and if this change should occur before the complete absorption of the effusion, this will remain permanently enclosed in an osseous sac.

As some of the above-named causes of thoracic contraction are equally present in pleurisies accompanied by other forms of exudation, so we find these contractions in and after their cure, although, generally speaking, they are not so distinctly marked. Thus we observe a slight contraction when the visceral lamina of the exudation has become organized into extensible and yielding areolar tissue, and when, notwithstanding that the lung has regained its original size, the costal lamina has been converted into a thick fibrous sheath; in this case the contraction is consequent on the condensation and shrinking of this lamella. Moreover, after pleurisies with an inconsiderable amount of plastic coagula, and with purulent exudation, we observe thoracic contraction; this is then produced, on the one hand, by paralysis and atrophy of the lung, caused by the long-continued pressure of a large quantity of exudation, and on the other, by the paralysis and consequent histological alteration of the intercostal muscles, which keep equal pace with the intensity and duration of the inflammatory process, and with the quantity and coagulation of the exudation.