Tuberculous Infiltration, when associated with the above-described metamorphosis of interstitial tubercle, usually softens with very great rapidity, and by hastening the progress of the disease, constitutes what is termed florid, or, by English writers, galloping consumption. It causes the most frightful destruction of the pulmonary tissue, and gives rise to caverns of irregular form, which are surrounded by rotten, and as it were corroded parenchyma, infiltrated with tubercle and breaking down into pus. Tuberculous infiltration is most commonly deposited in the superficial portions of the lungs, and hence it is the caverns arising from this variety which most frequently open into the cavity of the pleura. There are several ways in which this may take place.

(a.) The pulmonary pleura may be puffed up by the air rushing into the cavern, and may be violently peeled off the tuberculously-infiltrated parenchyma for some distance beyond the extent of the cavern, so as to form a flattish, round bulla, which finally bursts.

(b.) It may be converted, as we have already shown, into a yellowish-white eschar, which either tears or becomes detached unbroken.

(c.) Both the pleura and the infiltrated parenchyma surrounding the cavern may be attacked with gangrene, and become changed into a dirty-brownish, or greenish, pulpy, shreddy, fetid mass.

This last-named termination is especially worthy of notice, as it may occur not only near the surface, but also in the deep-seated portions of the tuberculous infiltration, especially around a pre-existing cavern. Moreover, in consequence of the frequency with which intense tuberculosis of the bronchial glands is combined with tuberculous infiltration, it may occasionally happen that a communication may thus be established between a deep-seated pulmonary cavern and a cavern in a bronchial gland.

The contents of tuberculous caverns present many differences. Sometimes, and especially when the infiltrated tubercles begin to soften, these caverns contain a yellow and somewhat thickish pus; more frequently, however, they contain a thin, whey-like fluid (tuberculous ichor), in which may be observed numerous grayish and yellowish, friable, cheesy, purulent flocculi and particles, whose quantity, however, is not in itself sufficient to explain the profuse expectoration which so often occurs in phthisis. This fluid is often of a grayish-red, or reddish-brown, or chocolate color, from the admixture of blood; or of an ash or blackish-gray color, from the pigment which it takes up during the softening of the tissue. Moreover, the caverns sometimes contain smaller or larger fragments of lung, resembling the parenchyma contained in their walls, and chalky concretions are occasionally found in them. In other cases they contain coagulated or fluid blood in various stages of discoloration.

This metamorphosis of pulmonary tubercle, in its twofold form, constitutes, as has been already observed, tuberculous pulmonary phthisis. If we now direct our inquiry to the state of the lung-substance around the tubercles and their abscesses, and from thence to the other organs and systems, in a distinct and uncomplicated case of this nature, we shall arrive at the following conclusions, in addition to what has been already stated, as the result of an anatomical examination when considered in reference to the living organism.

In the upper lobes, and especially in their upper third, there is usually a large cavern, surrounded inferiorly by several smaller ones, some of which communicate with it; between these are yellow tubercles in the act of softening, and gray tubercles just becoming opaque and discolored, whilst in the lower portions, as well as in the inferior lobes, there is a comparatively small sprinkling of gray, crude, tuberculous granulations.

The lung-substance between the tubercles is found in various states, according to the progress made by the disease. It may be normal, but generally there is a vicarious emphysema developed in its superficial portions, while the deep-seated parts are not unfrequently hyperaemic, or in a state of oedema. It is, however, sometimes atrophied, and this is a more important change, owing in part to interstitial inflammation, in part to the obliteration of the bronchial tubes and air-cells, in consequence of the pressure exerted on them by the accumulated tubercles, and in part to the occlusion of the bronchi by the blennorrhoeal mucous secretion when bronchial catarrh is simultaneously present. Inflammation (croupous pneumonia), which sometimes attacks the greatest portion of the non-tuberculous parenchyma, is also an important change; it appears partly as a brownish-red, and partly as a grayish-red hepatization, which is everywhere converted into yellow tuberculous infiltration, which becomes dissolved, and collects in vomicae; or the pneumonia may cause the deposition of a gelatino-glutinous product. (See p. 73.) In well-marked cases of this nature, the lung appears very bulky, and is coated with a grayish-yellow and generally thin pleuritic exudation, through which and the pulmonary pleura may be seen the peripheral tuberculous infiltrations, and the emphysematous patches amongst them.

In the larynx we find tuberculous ulcers, which vary in number and extent; and, associated with them, we find aphthous erosions, especially on the tracheal, and sometimes also on the pharyngeal mucous membrane.

The bronchial tubes proceeding to and from the caverns, exhibit streaks of mucous membrane in a condition of tuberculous infiltration, and are themselves filled with tuberculous matter; moreover, they are always in a state of catarrh, with reddening and softening of their mucous membrane, and with a muco-purulent secretion, which constitutes the greatest part of the sputa which are expectorated in the course of phthisis. The bronchial glands are enlarged, and more or less tuberculous.

Externally we find pleurisies which present great variety in their extent, and in the character, mode of organization, and consequences of the exudation. They are the causes of the very acute pains in the chest to which phthisical patients are subject. Unless when they arise from superficial pneumonia, they are generally developed during the softening of the tubercles and the formation of the caverns, and are associated with the inflammatory reaction that is established in the adjacent interstitial pulmonary tissue. The most constant seat of these pleurisies is the conical apex of the pleura and the surface of the upper lobes generally; they thus correspond to the starting-point of tubercle and of its metamorphosis. They deposit an exudation which becomes organized into fibro-cellular cords, or into a thick, compact, fibrous investment, which covers the upper lobes from the apices downwards, in the form of a hood, and diminishes in thickness from above downwards, causing the lungs to adhere firmly to the costal walls, and thus affording a protection against the perforation that might otherwise be caused by large caverns.

With rare exceptions, we find tuberculous intestinal phthisis associated with pulmonary phthisis, and although the former is usually only a secondary affection, dependent upon the pulmonary phthisis, it sometimes exceeds it in the rapidity of its progress, and rapidly occasions very great and exhausting ravages. As a general rule, the lower portion of the ileum is the part originally attacked, and from thence the ulcers extend upwards along this division of the intestine, and downwards over the colon; in their progress upwards the ulcers sometimes reach as far as the stomach. Frequently, however, and especially at certain times, the tuberculosis not only predominates in the colon, but is almost exclusively confined to it, the ileum entirely escaping; and sometimes we may readily perceive that the ulcers which are simultaneously present in the ileum are of a more recent date than those in the colon. In addition to the tuberculous ulcers on the intestinal mucous membrane, we also find that the corresponding mesenteric glands are more or less tuberculous.