Chronic nasal catarrh embraces those more or less persistent affections of the nasal chambers whose symptoms resemble those of acute coryza. The term catarrh is inexact. It is used to include several diseases associated by a single characteristic--namely, the existence of an increased amount of mucous secretion upon the affected membranes. In order to understand the varieties of nasal catarrh, it is necessary to have clear conceptions of the uses of the nasal chambers. The normal performance of the function of respiration demands that when the mouth is closed the currents of air should pass through the nose. These currents, however, do not sweep over the entire nasal surfaces, but are confined to those portions which answer to the inferior meatus and the space bounded within by the septum, without by the median surface of the inferior turbinated bone, and above by the under surface of the middle turbinated bone. In the lower mammals this space is separated posteriorly by a transverse bony lamina which {43} effectively excludes the upper portion of the nasal chambers from the tract just named. Anteriorly, at the termination of the inferior meatus and the middle turbinated bone, the tract is in freer communication with the upper spaces. The passage thus briefly defined may be called the respiratory tract, and when it remains patulous no serious interference with nasal respiration can occur. The transverse diameters of the tract are subject to frequent changes, owing to the erectile character of the mucous membrane in its walls. But as long as the surfaces do not touch one another obstruction cannot exist. The passage, even when narrowed to a chink or line intervening between the median and lateral walls of the tract or between the floor and the roof of the inferior meatus, is sufficient evidence that there is room for the transit of the currents of air. The membranes themselves are subject to changes in form which are dependent upon the degree of development of their erectile tissue.