There can be drawn a fairly apt analogy between war and the invasion of the tissues of the upper respiratory tract by the organisms which give rise to the common cold. In accordance with this analogy, the invading forces in infections of the upper respiratory tract are the many pathogenic bacteria associated with respiratory disease. The defenses of the nose against such invasion are twofold—the front line, which consists of the mucous blanket and ciliated epithelium of the nasal mucosa, and the second line, represented in the natural immune responses of the tissues to such bacteria.
The importance of maintaining an adequate first line of defense has been stressed by Proetz,1 Hilding,2 Lierle3 and others. They have pointed out the factors which tend to break down these defense mechanisms. The fifth column activities of a dry hot atmosphere, of metabolic disturbances, of dietary insufficiencies and the like are well known