Circumscribed Or Partial Gangrene Of The Lungs appears in the form of gangrenous eschar, and is incomparably more frequent than the former variety. We find the parenchyma, at some spot of varying size, converted into a blackish or brownish-green, hardish, but moist and tough eschar, which adheres to the surrounding tissue, evolves, in a very marked degree, the peculiar odor of sphacelus, and, as Laennec observes, is extremely similar to the eschar produced on the skin by nitrate of silver. It is sharply defined, and, as we shall presently show, the surrounding parenchyma may be in various conditions.

The eschar becomes gradually loosened from the surrounding tissue, and rests in an excavation corresponding to it in size and form; it may be described as a blackish-green plug, which superficially is soft, shaggy, moist, and bathed in an ichorous fluid, but, towards its centre, is of a denser structure. More frequently, however, the whole or the greater portion of the eschar softens and becomes dissolved into a greenish-brown, very fetid, ichorous pulp, mixed with rotten, shaggy fragments of tissue, and enclosed in a cavity whose walls are lined by a shaggy tissue infiltrated with ichor.

The size of the gangrenous portion, at its commencement, varies from that of a bean to that of a hen's egg, or may be even larger; it is most commonly not smaller than a hazel-nut or larger than a walnut. The form is on the whole irregular, with a tendency to roundness. It is much more commonly seen in the superficial than in the deep layers of the lung, and more frequently in the lower than the upper lobes.

These eschars may either occur singly, or several may be simultaneously present.

The number and size of the bronchial tubes attacked by the gangrenous destruction, are usually proportional to the size of the original gangrenous centre; these bronchial tubes constitute the passage through which the gangrenous exhalation and the eschar itself, in the respective form of an intolerably fetid atmosphere around the patient, and of gangrenous, ichorous sputa, make their escape. The gangrene proceeds outwards, and attacks the pulmonary pleura the more quickly the nearer it was originally seated to the surface of the lung. If the gangrenous eschar becomes detached, it falls into the cavity of the thorax, unless there are firm adhesions at the spot; or else it becomes dissolved, and the ichorous semi-solid matter is effused into the pleural sac, and gives rise to pleurisy with ichorous exudation, and to pneumothorax, since the fetid gas evolved from the gangrenous mass either collects alone in the thorax, or atmospheric air finds its way through the bronchial tubes which open into the abscess, and thus mixes with the aforesaid gas in the thorax. These superficial gangrenous caverns may be recognized at a glance, for at these spots the pleura is either converted into a blackish-green eschar, whose inner surface is shrivelled and hard; or, if the eschar has already dissolved, the pleura is of a blackish-green color, rotten, and moist, and appears distended by the gas evolved from the abscess; or, finally, if the pulmonary pleura be ruptured at certain spots, or be perforated, or even perfectly destroyed, in consequence of spontaneous fusion, we shall observe the open, sunk cavern, either covered by the remains of the pleura, or thoroughly exposed, and more or less completely emptied.

A primary gangrenous abscess must be distinguished, when possible, from one that has undergone subsequent enlargement; very large abscesses are, as a general rule, not primary, but are formed by the corroding action of circumscribed gangrene, and do not, as we shall presently show-present the distinct line of demarcation which is observable in primary-abscesses.

The lung-substance surrounding the gangrenous abscess is sometimes normal, with the exception of a serous or sanguineo-serous infiltration; but when the gangrenous eschar dissolves, diffuse gangrene may be developed in it to a greater or less extent. More frequently, however, we see it in a state of reactive inflammation, varying in extent and character. Very often there is a simple stasis of an asthenic character; this gradually assumes an inflammatory type, which it retains for a long time, and then the stage of hepatization slowly and imperceptibly ensues. From a want of energy in this process of reaction, the primary gangrenous abscess may extend in various directions, so as often to attain the size of a man's fist, or even of a child's head, while the surrounding tissue becomes more or less rapidly discolored, without presenting any decided stratified appearance, and finally breaks down into a gangrenous, ichorous pulp. In this way the gangrene may extend outwards, until it reaches the pulmonary pleura, when it may give rise to the consequences which have been already enumerated; and indeed, if the lung be adherent, the costal pleura at the corresponding spot may be involved in the metamorphosis.

We often find a higher degree of inflammation set up in the surrounding tissue; it is in a state of decided hepatization, which sometimes extends over the whole of the lobe which is affected by gangrene. The disease not unfrequently proves fatal through this excessive reaction.

The most important process, however, occurs in the layer of tissue immediately surrounding the cavern, and is obviously an effort of nature to promote a cure. The reaction here appears as an inflammation of the interstitial tissue of the lungs, which, together with the cavernous walls, undergoes suppuration, and thus effects the removal of the sphacelated tissue which was adhering to the walls of the abscess.

In this process we find that at first only single or isolated patches of tissue become gangrenous, and the pus which is secreted from the walls of the abscess is still mixed with ichor, and gangrenous fragments of tissue. As the process advances, however, suppuration predominates, and after the gangrenous tissue has been ejected through the bronchi the cavern is converted into an ordinary suppurating, abscess, whose inner wall is infiltrated with pus; externally, for a distance varying from three to six lines, the tissue is of a grayish-red color and firm; and if croupous exudation in the air-cells be associated with the inflammation of the interstitial tissue, we observe a scarcely perceptible, very delicate granulation. If the suppuration in the inner stratum of the capsule now diminishes, the result of the whole process is a cavity, with whitish, cellulo-fibrous, callous walls, which sooner or later coalesce, leaving merely a cicatrix, like ordinary abscesses or tuberculous vomicae. In some rare cases circumscribed pulmonary gangrene undergoes a cure in this manner.

If the eschar breaks down, and dissolves very rapidly, and little or no reaction be developed in the surrounding parts, or if the primary cavern enlarge very quickly at the expense of the surrounding parts, the gangrenous destruction not unfrequently involves large, unobliterated bloodvessels, and gives rise to exhausting haemorrhages into the cavern, the bronchial tubes, or even into the thoracic cavity, when the abscess has opened into the pleural sac.

Partial gangrene often arises in the perfectly healthy lungs of weak, decrepit, cachectic persons from general depressing influences, and is developed from a circumscribed passive stasis. Under similar circumstances, we find it associated with pneumonia in its various stages, with pulmonary abscess, with pulmonary tuberculosis and tuberculous vomicae, with bronchitis, especially when it is developed in the course of exanthe-matous diseases, both in adults and children, etc. Finally, it appears among the sequelae of typhus, as a manifestation that the typhous process is spontaneously degenerating into a state of putrescence; or it may be produced by the absorption of gangrenous ichor from gangrene of different parts into the blood, in which case we have diffluent gangrenous deposits, or septic capillary phlebitis.