DEFINITION.--Tumors, benign or malignant, growing from the wall and projecting into the interior of the windpipe. Inversion of the mucous membrane forming a protrusion into the interior will be spoken of under the head of Stenosis; and tumors of other organs extending into the trachea, such as cancer of the oesophagus, lymphatic glands, thyroid body, etc., are excluded from consideration under the present head. FREQUENCY OF OCCURRENCE.--Aside from post-tracheotomic granulation-tumors, which with careless tracheotomy or after-treatment occur often, the disproportion in the frequency of laryngeal and tracheal morbid growths is even greater than that of other laryngeal and tracheal affections. I have met with only eight instances of tracheal morbid growths, strictly so called, in a special practice during more than twenty-five years. This is exclusive of post-tracheotomic vegetations and tumors from contiguity. ETIOLOGY.--Local irritations and chronic inflammatory conditions seem often, if not always, to be the forerunners of tracheal tumors, but the real cause of the latter is unknown. Recently it has been suggested (see the article on LARYNGEAL TUMORS) that the ever-present bacilli play a rôle in the production of morbid growths as well as in that of other diseases. As it is known that some parasitical organisms on plants use up their nidus very slowly, with the formation of peculiar excrescences, while others very rapidly destroy the tissue of their host, it would be easy to suppose that some such difference in the micro-organism causing the tumor determines its benign or malignant character. Post-tracheotomic vegetations may arise from the irritating pressure of a {140} tracheotomy-tube, especially from the use of a fenestrated tube or a tube ill fitted to the patient. Some observers are of opinion that such tumors existed before the performance of the operation, and, indeed, led to it, even though the supposed reason may have been laryngeal or some other tracheal disease. While it cannot be denied that such may have been the case sometimes, there is no doubt that in other instances--and not only in those in which the vegetations "always grow from the cicatrix" (Petel)--they are truly caused by the operation, or by the wearing of the tube, especially if it be in any way unsuitable as to size, form, etc.