lOt PROCEEDINGS OF SOCIETIES. 



mass, of from half a line to five or six lines in thickness. It ia 

 ususilly firmly adherent to the subjacent membrane, upon which it 

 is moulded ; is moi-e or less friable, so tliat when traction is made 

 upon it with a pair of forceps, it comes away piecemeal, or in a 

 layer somewhat resembling felt or chamois leather. If forcibly 

 detached, a breach of surface is made, and bleeding generally 

 follows its separation, as the mucous membrane is much 

 congested. 



The croupous cast, on the other hand, is semitransparent, 

 delicate, and tender to handle, often gelatinous or white-of-egg- 

 like, and of a pale yellow colour ; easily separable from the sub- 

 jacent surface, as an imperfect cast of the part on which it is 

 formed, and never so closely connected with it, as to cause bleed- 

 ing when removed. It is, in short, a simple epithelial layer closely 

 resembling the skin shed by some of the lower animals — an out- 

 growth of epithelial cells undergoing degeneration of protoplasm 

 and entangling granular molecules. 



As to the histological characters, in diphtheria the normal 

 tissues are seen to be replaced by an aggregation of compressed 

 cells, molecules of fat, connective or fibrous tissue, a few crystals 

 muco-purulent or granular corpuscles, foreign bodies as starch 

 granules, or other portions of food, and spores of Oidium 

 albicans. It is surmised, therefore, that the felt-like membrane 

 is made up of superficial and deep tissues ; mucous membranes, 

 voluntary and involuntary muscles, and glands, and produces 

 great tension and decomposition, or ulcerative destruction. Not 

 a trace of columnar epithelium was seen in any specimen. 



The croupous cast is seen under the microscope to consist of 

 pavement and cylindrical or columnar epithelium, and is a trans- 

 parent albuminous substance entangling the scattered contents of 

 epithelial cells, molecular matters, fat and mucous corpuscles, 

 and a few foreign bodies, as starch, granules involved in a homo- 

 geneous matrix. The columnar epithelium retains its cilia, each 

 cell being filled with clear protoplasmic and nucleated contents. 

 Fungus spores are rarely found in these films, which appear to 

 partake of the nature of an extensive cell proliferation rather 

 than of a transudation or true exudation. 



The objects were partly examined in the fresh state, partly 

 stained and dried ; fine sections being then made and mounted 

 in dammar or Canada balsam. 



