The product of superficial inflammations may lie on the surface, as in the case of inflamed mucous membranes, or immediately below the surface, as in numerous cutaneous inflammations, of which erysipelas may serve as the type. The term catarrhal, applied to superficial inflammations, carries with it the idea of displacement, flowing, of the exudation. The product of a catarrhal inflammation must be largely liquid, that such a displacement may readily take place, and the catarrhal exudation is chiefly composed of an excess of those elements which are present in the normal, physiological secretion from the membrane concerned. Mucus therefore represents a frequent constituent of the catarrhal exudation, and mucous as well as muco-purulent catarrhs of the gastro-intestinal, bronchial, genito-urinary, and other mucous membranes are recognized. The catarrhal inflammation of the respective membranes usually represents the mildest form, as it demands an intact epithelium, and a ready removal of the inflammatory product. As the cause of a catarrhal inflammation may occasion a destruction of the epithelium or a necrosis of the mucous membrane, the frequent association of catarrhal with fibrinous or diphtheritic inflammations is obvious. In such cases the clinical importance of the latter varieties gives them the precedence in the designation of the inflammation. The retention of the catarrhal products is the frequent cause of permanent disturbances of a more or less serious nature. These result in part from the mechanical obstruction offered to the function of parts beyond the seat of obstruction, as pulmonary atelectasis; and in part from the changes taking place in the retained product. Purulent otitis media with its dangerous or fatal results, and gangrene of the lung terminating in septic pleurisy, are not infrequent instances of severe disturbances from putrefaction of the retained products of a primarily catarrhal inflammation. A cheesy degeneration of the catarrhal cells leads to a surrounding fibrous, or destructive, inflammation, with a corresponding diminution in the function of the organ affected. Of the deep-seated varieties of inflammation, that requiring special mention is the phlegmonous form. This runs its course within the less dense fibrous tissue known as the areolar or cellular tissue. The term cellulitis is usually employed by English writers to indicate the seat and nature of the process, and although the use of the term cellular tissue is rapidly becoming obsolete, the convenience of cellulitis favors the retention of the latter name.