This name, as well as that of Plastic bronchitis or Bronchial croup, is given to a condition of very rare occurrence and of rather obscure pathology, but yet of great interest. We have seen that in laryngeal and tracheal diphtheria the fibrinous exudation sometimes extends down into the bronchial tubes, and that casts of these are formed occasionally. Taking the other end of the bronchial tree we find that in acute pneumonia the fibrinous exudation which forms in the lung alveoli commonly extends some distance into the finer bronchi, and so we find casts in them. But there are cases in which fibrinous casts form in the bronchial tubes independently, without any disease of the trachea on the one hand or of the lung proper on the other. These cases are somewhat chronic in character, and the expectoration of casts occurs at intervals during months or even years. The casts are of a whitish grey colour and represent the bronchi of, it may be, a single lobe, with their ramifications. These can be seen very beautifully by floating them out in water. Sometimes the fine ends of the casts are swollen out as if they had come from the alveoli. The casts sometimes present on section a stratified arrangement as if the fibrine had been deposited in layers. They show under the microscope fibrine with leucocytes.
The exact pathology and the source of this exudation are somewhat obscure. In some cases where death has occurred shortly after the expectoration of the casts, or where they have been found in situ, there has been little perceptible alteration of the mucous membrane. This has led some to suppose that the fibrine corned from the lung alveoli, and in'many cases the lung tissue is considerably altered; there may be phthisis, or pneumonia, or collapse. But it is not apparent to what extent these may be secondary to the bronchitis. A possible indication of the pathology may be afforded by the fact that in a considerable proportion of the cases there has been haemorrhage from the lungs.