The nature and consistency of the pseudo-membrane in the larynx is best studied by the light of the study of its anatomy. There is a great deal of elastic tissue in both epiglottis and larynx; the mucous membrane of the latter is thin, and sometimes folded on the vocal cords. The epithelium of the epiglottis is pavement; only at its insertion it is cylindrical. In the larynx it is also pavement on the true vocal cords and in the ary-epiglottic folds, and fimbriated toward the fossæ Morgagni and trachea. Lymph-vessels are but scanty on the epiglottis, still more so in the larynx. Of acinous muciparous glands there are none on the epiglottis, none on the true vocal cords; they are more frequent in and round the fossæ Morgagni, with cylindrical epithelium in the glandular ducts. The trachea and bronchi contain a good many elastic fibres, less connective tissue, fimbriated epithelium, some lymph-vessels, but no lymph-glands, and acinous muciparous glands in large numbers. Wherever the pavement epithelium membrane is abundant the membrane is firmly adherent and imbedded into the mucous membrane. Where it is cylindrical and plenty of acinous glands secrete their mucus, they are loosely spread over the mucous membrane, from which {101} they can be easily removed; while the histological condition of both the imbedded and the loose membrane is exactly the same. Before the membranous deposit takes place the surface is in a condition of catarrh. Round the membrane the mucous membrane is red and slightly swollen. Not always, however, is that so. Particularly, the epiglottis may be covered on its inferior surface with a solid membrane or be studded with tufts of membrane, without much or any hyperæmia. The same can be said of the larynx, which is supplied with but a scanty distribution of blood-vessels and a sufficient network of elastic fibres to counteract the dilatation of blood-vessels peculiar to the catarrhal and inflammatory processes. In uncomplicated cases of membranous laryngitis the membrane is confined to the larynx. Dozens of years ago--viz. before 1858, when diphtheria began to settle amongst us, never, it appears, to give up its conquest again--that took place in most cases. But since that period we meet with few such simple cases. As a rule, the membrane makes its appearance in the pharynx first, from there to descend into the larynx, and not infrequently into the trachea and bronchi. In other--fortunately, but few--cases the membrane is formed in the bronchi and trachea first, and invades the larynx from below. Other organs suffer but consecutively and from the results of impeded circulation only. Thus, in post-mortem examination hyperæmia of the brain, liver, and kidneys, and bronchitis, broncho-pneumonia, or pulmonary oedema, are met with. Only those cases of membranous laryngitis which are complicated with general diphtheria yield the additional changes of the latter.