n. An infectious disease, characterized by the formation over the affected and inflamed parts of a firm whitish or grayish pellicle, or false membrane (which is removed with difficulty and leaves a raw surface), and by general prostration.n. Diphtheria is caused by a specific bacillus, called Bacillus diphtheriæ, or the Klebs-Loeffier bacillus, which usually can readily be detected in the exudate by microscopical methods. The search for this organism has become a routine measure in doubtful cases of inflammation of the upper air-passages, and often a positive diagnosis of such conditions can be made only in this way. The disease begins with swelling and redness of the throat, fever, and loss of strength. The false membrane appears early and may be confined to the tonsils or may spread to the mucous membrane of the nose, pharynx, or larynx. When the larynx is involved, the breathing becomes difficult, and suffocation may ensue. Formerly the only means of saving life in this complication was tracheotomy, but this has been almost entirely superseded by intubation. The disease may be followed by paralysis, by weakness of the heart, or by disease of the kidneys. Treatment, both curative and preventive, consists in the subcutaneous injection of diphtheria antitoxin — one of the earliest instances, and still the most effective instance, of serum therapy. See cut under Klebs-Loeffler *bacillus.