Tubercle is very commonly met with in the air passages, but it is found in some parts of them much more frequently than in others. The most common position is in the the larynx; it is very rare in the trachea and larger bronchi; while, again, it not uncommon in the ultimate ramifications of the tubes. On softening it gives rise to tuberculous ulceration, and to laryngeal, tracheal, or bronchial phthisis, according to the seat of the deposit.

Tuberculosis of the larynx, as a primary and independent affection, is so extremely rare that we feel inclined to doubt its existence. It is almost invariably developed as a consequence of pulmonary tuberculosis, and then, as a general rule, not until the affection has established itself as a pulmonary phthisis, and made considerable progress. The seat of tubercle is almost constantly and exclusively the mucous membrane and submucous areolar tissue lying over the transverse muscle and the adjacent arytenoid cartilages; it occurs, however, exceptionally at other spots, as for instance, the anterior surface of the epiglottis. It is either deposited in the form of gray granulations in the submucous areolar tissue, or as yellow, caseous, friable, tuberculous matter, is infiltrated into the mucous membrane; in either case, however, and especially in the latter, it rapidly softens, and ulceration is established. The softened, gray granulations form small roundish ulcers, varying from the size of a millet-seed to that of a lentil, with raised, hard edges. These unite with one another, and give rise to a secondary form of ulcer, irregular in shape, with pouch-like indented edges, and a cellular, callous, thickened base, both of which may become the seat of secondary tuberculous deposit. The tuberculous infiltration becomes disintegrated in the mucous membrane, and forms therewith an extremely irregular and, as it were, gnawed and fissured ulceration, presenting obvious signs of reaction, namely, "redness, injection, swelling, oedema of the tissues, and aphthous exudation over the adjacent parts.

The ulcer enlarges in consequence of secondary tuberculous deposition at its edges and the surrounding parts, as well as on its base, superficially as well as deeply; it thus gives rise to ulcerations which extend over the whole larynx and epiglottis, upwards to the soft palate and root of the tongue, downwards to the trachea, and inwards, causing suppuration and necrosis of the fibrous tissues and of the cartilages. They may even perforate the larynx from within outwards, and give rise to emphysema.

The secondary tuberculous ulcer is sometimes distinguishable by a condylomatous development of the mucous membrane at its edges, and of the islets of mucous membrane, which, as the ulcer enlarges, are frequently left on its base. It is not improbable that, in these cases, the tuberculosis is combined with syphilis.

There can be no doubt that in some rare cases, and under the requisite general conditions, tuberculous ulcers of the larynx are healed; but they always leave an unshapely cicatrix, puckered in proportion to the extent of the ulcer, and callous in proportion to its depth. We must, however, be careful not to regard all the cicatrices which we may find in the neighborhood of true tuberculous ulcers in the larynx and trachea, as the cicatrices of so many tuberculous ulcers.

Tuberculosis of the Trachea is extremely rare, it being only seldom that the corresponding laryngeal affection extends itself in a tuberculous ulcer to the upper part of the canal. In laryngeal phthisis we often, however, meet with small ulcers on the tracheal mucous membrane, and frequently in such numbers that they present a confluent appearance. These are the ulcers to whose cicatrices we referred, as liable to be mistaken for the cicatrices of tuberculous ulcers. They are small, shallow ulcers, most commonly of an oval but sometimes of a linear form, with a very slightly concave base; the depression being so trifling that it is sometimes only detectible when the light falls obliquely on it: this base presents a raw and excoriated appearance, is of a pale or dark red color, and is either exposed or coated with a creamy, diffluent exudation of a croupous nature; and it is surrounded by a fiery redness, or by a sharply defined red areola. They are most commonly situated on the posterior wall of the trachea, and frequently extend into the bronchial trunks, and we often find them much more numerous on one side (that, namely, in which the most diseased lung is situate) than on the other; moreover they are found with tolerable frequency in the pharynx and on the mucous membrane lining the mouth. They present nothing in common with tuberculous ulcers, and consist, as is at once seen, in an exudative aphthous process which is frequently associated with florid, laryngeal phthisis. If the tuberculosis be in a state of arrest, or actually retrograding, the above-described erosions become replaced by delicate, whitish, glistening, radiating, or star-like cicatrices.