DIAGNOSIS.--The symptoms mentioned are those common to nearly all cases of tracheal stenosis, and will be referred to again under that head. Tracheoscopy alone makes the diagnosis certain; unless when the seat of the disease is ascertainable without, its nature is shown by the expectoration of portions of the tumor. The first case of tracheal tumor ever diagnosed during the patient's life was observed by means of the mirror by Tuerck in 1861; but it is very difficult in the mirror to estimate distances as to depth, and unless the number of tracheal rings above a tumor can distinctly be counted, a growth in the lower cavity of the larynx may readily be mistaken for one in the trachea, and vice versâ. Catheterism of the trachea shows the distance at which the tumor is situated, sometimes very accurately, but it is dangerous unless performed under the guidance of the mirror, and even then requires great care. The introduction without the mirror of a probe or sound for the same purpose is still more dangerous and unjustifiable, while with the mirror it is perfectly safe in proper hands. Localized protrusion of the mucous membrane into the interior is the condition which most simulates tracheal tumor. (Compare Fig. 32.) [Illustration: FIG. 31. Papilloma of Trachea.] The pathological nature of a tracheal tumor can sometimes be determined in situ with more or less probability. Without microscopical examination it is not always possible to say whether a growth is benign or malignant unless the mass has advanced to ulceration, and then specific disease must be excluded by the history and concomitant symptoms. Papillomata have a peculiarly uneven surface; fibromata are usually more smooth. With equally good illumination, tumors of the trachea resemble tumors of the larynx, and may be similarly differentiated. The former are almost always non-pedunculated, or at least none of those hitherto observed have had a long pedicle. Their seat is generally the posterior wall, or the cicatrix of the anterior wall after tracheotomy. In Fig. 31 is seen the tracheoscopic appearance of one of my cases of tracheal papilloma. PROGNOSIS.--The prognosis is always unfavorable in malignant cases, and also in non-malignant when the tumor grows rapidly or has already attained a large size. The introduction of the laryngoscope has bettered the prognosis, inasmuch as in many cases early recognition enables us, by performing tracheotomy, to prevent sudden death from suffocation, and also because by the aid of the mirror removal has been accomplished through the natural passages.