PATHOLOGY.--Pseudo-membranous laryngitis is characterized by the presence, on and in the mucous membrane, of a pseudo-membrane of a whitish-gray color, various consistency, and different degrees of attachment. It has been called croupous when it was lying on the mucous membrane without changing much or at all the subjacent epithelium and could be removed without any difficulty. It has been called diphtheritic when it was imbedded into the mucous membrane and was difficult to remove. This difference exists, but it does not justify a difference of names except for the purpose of clinical discrimination; for the histological elements of the two varieties are the same, and the difference in their removability is explained by the anatomical conditions of the territory in which they make their appearance. The membrane consists of a net of fibrin studded with and covering conglomerates of round cells, mixed with mucus-corpuscles, epithelial cells more or less changed, and a few blood-cells. The fibrinous deposit is either quite superficial or lies just over the basal membrane or on layers of round cells originating from the basal membrane. It is continued into the open ducts of the muciparous follicles, filling them entirely in the worst cases, or meeting the normal secretion of mucus in the interior of the duct. The principal seat of the pseudo-membrane is that mucous membrane which is covered with pavement epithelium; thus it is that the tonsils are the first, usually, to exhibit symptoms of diphtheria. But cylindrical epithelium is by no means excluded. However, while pavement epithelium is generally destroyed by the diphtheritic process, the cylindrical epithelium is frequently found unchanged, or but little changed, on top of the mucous membrane under the pseudo-membrane.