There is doubtless a disposition on the part of the erectile tissue to grow in the direction of the least resistance, and thus to occupy, by a process of compensative hypertrophy, the spaces left as the result of variations or defects in development in the bones composing the framework of the nasal chambers. The greater development of the erectile tissue may in this way be found on the side answering to the larger respiratory tract, which may therefore be more apt to suffer from changes in the conditions of nasal breathing than the chamber having the smaller tract. The erectile tissue acts as a monitor to the throat and lungs by presenting warm surfaces over which the air passes, thereby having the temperature raised before it enters the throat and lungs. It also acts by occluding the chamber, and thus aids in shutting out irritant vapors and dust. The lower animals possess a higher degree of development of the tissue at the point where the adducted ala presses against the septum. This point answers to the position of the organ of Jacobson. With man, the locality of the adduction corresponds to the junction of the premaxillary with the maxillary portion of the nasal chambers, and is often the seat of a delicate band of mucus extending across from the inferior turbinated bone to the septum. That portion of the nasal chamber above the respiratory tract may be called the olfactory tract. It does not appear to be involved in the diseases under consideration, or, if it is, no clinical signs or symptoms are presented with which the author is acquainted. It will therefore receive no attention in this article. For convenience the varieties of chronic catarrh may be classified as follows: FIRST VARIETY--that dependent on defective nasal respiration. This variety is caused by-- _(a)_ Osseous obstruction in the nasal chamber. _(b)_ Membranous obstruction in the nasal chambers from compensatory hypertrophy of the erectile tissue, alone or with hyperplasia. _(c)_ Obstruction arising from hypertrophy of the adenoid tissue in the pharyngeal vault. _(d)_ Contracture of the levator palati muscles. SECOND VARIETY--that dependent on structural changes in the component parts of the nasal chamber. This variety is associated with-- _(a)_ Chronic inflammation of the nasal mucous membrane without hypertrophy of the erectile tissue. _(b)_ Atrophy of the turbinals and their associated mucous membrane. _(c)_ Necrosis of the bones which enter into the framework of the nasal chambers. FIRST VARIETY.--Defects in nasal respiration induce hyperæmia, distension of the erectile tissue, hyperplasia of the mucous membrane, and {44} inevitable distress in the nose. A sense of fulness across the bridge of the nose and at its sides is complained of. Frontal headache may be present.