THE DIPHTHERITIC MEHRRANE.—The membrane is most frequently seen upon the tonsils, soft palate, uvula, pharynx, nares, larynx, trachea, or bronchi. In severe cases it may appear upon the lips, especially at the angles of the mouth, the buccal mucous membrane, and the tongue. Very rarely it appears in the oesophagus, stomach, or intestines. In fact, the freedom of the oesophagus, when the diphtheritic membrane may be seen completely covering the pharynx and tonsils and extending throughout the whole respiratory tract even to the ter minal bronchi, is most remarkable. Even in the severest cases the membrane usu ally stops abruptly at the beginning of the cesophagus.
It is also possible to observe a true diphtheritic membrane upon abraded cutaneous surfaces; upon wounds, as in tracheotomy; or upon the conjunctiva or the genital mucous membrane. The color of the membrane may be white, gray, greenish white, yellow, or more or less black, when there has been luemor rhage from the affected surfaces. It may be thick and elastic, so as to be stripped off in sheets, or thin and diffluent. The thicker membrane is observed upon the surfaces covered with columnar epithe ilium, with a definite basement-mem brane, such as the nose, larynx, trachea, and bronchi. Here, too, it is but loosely attached; so that it is often thrown off in casts during life, or after death may easily be stripped off from the under lying surfaces. Upon the tonsils, pharynx, uvula, and fauces, where the epithelium is of the squarnous variety and without a basement-membrane, the diphtheritic membrane is much more closely attached. Often in these situa tions we see, after death, no distinct membrane, but a difiluent exudate, which may be easily washed off, leaving a dis tinctly-ulcerated surface beneath.
Microscopically the membrane or exu date is found to consist chiefly of fibrin, mingled with epithelial cells from the mucous membrane, pus-cells, red blood cells, granular material, and bacteria. The superficial parts of the membrane I are granular in character, while beneath we find a more or less distinct net-work of fibrin, inclosing within its meshes the cells, granular material, and bacteria. The bacteria are the diphtheria bacilli together with streptococci or staphylo cocci, and rarely pneumococci. The in flammatory process may be superficial or may extend irregularly into the mucous membrane, in some cases involving the submucous tissue and even the muscular coat. The bacteria may likewise pene trate deeply into the tissues, but are usually most abundant in the superficial parts of the membrane. The epithelial cells of the mucous membrane undergo degeneration, their protoplasm becoming granular, their nuclei fragmented, and the cells ultimately breaking up into granular material. The pathological
process is, therefore, a coagulation-ne crosis involving the mucous membrane more or less deeply.
The pseudomembrane is cast off in masses or is gradually disintegrated, with more or less destruction of the mucous membrane. The process of separation is usually attended by a more abundant ' cellular exudation beneath the pseudo- ' membrane. Except in the gangrenous cases apart from the tonsil, in which • there may be extensive destruction of the tissues, the integrity of the mucous membrane is completely restored, leav ing no traces of the preceding disease. Gangrene is not properly a part of the diphtheritic process, but is brought about either by especially-unfavorable condi tions affecting the vitality of the patient and by the invasion of unusually-virulent bacteria other than the diphtheria ba cilli, probably the streptococci.
The seat and distribution of the mem brane vary greatly in different cases. The point of importance with reference both to symptoms and prognosis is the involve ment of the larynx. Of 1000 cases ana lyzed by Lennox l3rowne, the larynx was involved in 159, in only 4 of which num ber was the affection limited to the larynx. In a similar analysis of 109 cases by Holt, the larynx suffered in 46, in 10 of which the disease involved either the larynx, or the larynx with the trachea or bronchi. Holt gives no purely nasal eases in his series; 2 are given by Browne. In the great majority of cases the mem brane is found upon the tonsils or the adjacent parts, the pharynx, uvula, and pillars of the fauces. Six hundred and seventy-two of l3rowne's 1000 cases showed such distribution.
Since extension of the membrane usually increases the severity of the case and the probability of death, the clinical records of Browne show the comparative frequency of the various forms better titan tables which are largely formed from autopsy records. Laryngeal cases are also much more frequently met with in children's hospitals or asylums than in dispensary or private practice.
In cases involving the nasal cavities the process is often catarrhal, and there may be no macroscopical lesion after death. In many such cases, however, there may be membrane in the rhino pharynx, the adenoid tissue of the vault of the pharynx being a favorite seat of the disease. When membrane is devel oped in the nose, it is usually thick and hut loosely attached; so that it may readily be thrown off as casts of the