Gangrene Of The Pleura occurs in consequence of its being denuded by accumulations of pus or ichor in the costal or pulmonary wall. The pleura then assumes the appearance of a yellowish-white, or more frequently of a blackish or greenish-brown, lax or deliquescent slough, with superficial gangrene of the lung. There is no difficulty in distinguishing it from the acute black softenings to which the pleura diaphragmatica is subject from the stomach, or the left layer of the mediastinum from the oesophagus.

C. Adventitious Products

Passing over the areolar and areolo-serous adventitious products, we must notice anomalous fibrous and cartilaginous tissues, and anomalous osseous substance. These are especially frequent in the pleura, and in relation to their origin and their seat they present two distinct varieties. In one case they are products of inflammation, which, as has been already stated, become converted into fibroid and cartilaginous tissues, and then into concretions of bone-earth in the form of strings and plates; these are seated on the inside of the pleura, with which they intimately coalesce. In the other case, the fibroid and cartilaginous tissues are developed independently of inflammation, and merely in consequence of a hyperaemic condition in the subserous areolar and fibrous tissues, and in the tissue of the serous membrane itself. We first observe a whitish, more or less circumscribed opacity and condensation of the serous tissue; there is here a development of tissue resulting in the formation of a smooth or nodular elastic plate, or of a group of granulations of fibrous or fibro-cartilaginous tissue, or even of irregularly shaped masses, which vary from the size of a pea to that of a nut, and finally ossify. These are always situated under or on the outer side of the serous membrane, and are invested by it.

These two varieties may be easily distinguished from one another: fibrous exudations invest the costal as well as the pulmonary pleura; they ossify, however, only on the costal pleura. Subserous adventitious products occur almost exclusively on the costal and diaphragmatic pleura, and their most common seat is in the intercostal spaces. They sometimes become liberated, and are found free in the cavity of the thorax, in the form of round, nodular masses of cartilage.