'i2'2 MUCOUS MEMBRANES. 



impression conveyed is that of a substance exuded upon tlie 

 mucous surface, and coagulated at once by contact vritli the 

 air. For the material in question furnishes a characteristic 

 membranous investment for the mucous membrane (" false 

 membrane ") which adheres to the surface as closely as gypsum 

 to a mould. The under surface of the false membrane presents 

 an accurate impression of every irregularity of the mucous 

 surface ; should the entire circumference of the mucous tube 

 have been involved, the false membrane forms a tubular cast ; 

 should the canal have been of small calibre, the cast is solid and 

 cylindrical ; should the disease have been circumscribed, it forms 

 a rounded plaque. In thickness, the false membrane varies 

 from a mere bloom -like efflorescence to a rind a line in depth ; 

 it sometimes presents a I'eddish mottling, due to minute extrava- 

 sations occurring simultaneously with the exudation. 



§ 363. All the remaining properties of the false membrane, 

 particularly the histological quality of the seeming fibrin, and 

 the firmness with which the membrane adheres to the mucous 

 surface, vary with its place of origin, and find their explanation 

 in the normal structure of the affected part. Of all the mucous 

 membranes of the body, none is more liable to croupous inflam- 

 mation than that of the larynx ; next in order of frequency 

 come the tracheal and pharyngeal mucous membranes, whose 

 liability is nearly on a par, so that ^Ye find laryngeal croup com- 

 ])licated, now with croup of the air-passages, now with that of 

 the pharynx ; enabling us to distinguish between a laryngo- 

 tracheal and a pharyngo-laryngeal variety. At the bed-side the 

 former is termed ^^ croup" (Braune) par excellence; the latter, 

 most erroneously, "diphtheria" (diphtheritis, Rachenbraune, 

 pharyngeal croup). The physician has every reason to keep the 

 two varieties apart. In their clinical characters, in the dangers 

 to which they expose the patient's life, and above all as regards 

 their treatment, they differ so essentially, that in spite of their 

 anatomical identity, on which it is my business to insist, I should 

 feel bound to oppose any attempt towards a clinical fusion of 

 the two diseases. 



§ 364. We w^ill begin by discussing pharyngeal ceoup, 

 commonly called diphtheria. The morbid process is always 

 insular. At various points of the isthmus faucium, soft palate, 

 and uvula, of the tonsillar surface, palatine arches, and glosso- 



