430 MUCOUS MEMBRANES. 



as the membrane does not merely become fluid at its edges, but 

 exhibits thinning and perforation at various points in its con- 

 tinuity as well, the perforations ultimately becoming confluent, 

 I have only seen one case of this kind ; I recollect that the fluid 

 l^roducts of softening yielded a precipitate of mucin on the 

 addition of acetic acid ; and this led me to speak of a ^^ mucoid "^ 

 softening of the false membrane. 



§ 369. Having discussed the croupous process as it presents 

 itself in the pharynx and trachea, we may conclude with a few 

 words about laryngeal croup. A croupous inflammation, con- 

 fined, throughout its entire course, to the larynx, is of rare 

 occurrence ; iievertheless, the laryngeal is the most common 

 variety of croup, inasmuch as it nearly always complicates croup 

 of the air-passages, and may also complicate that of the pharynx. 

 Tlie characteristic features in the morbid anatomy of laryngeal 

 croup are due to the fact that the mucous lining of the larynx 

 agrees in its structure, partly with that of the pharj^nx, partly 

 with that of the trachea. Both surfaces of the epiglottis, and the 

 true vocal chords, are coated with a laminated pavement-epithe- 

 lium, which is not marked ofl" from the connective tissue by any 

 homogeneous basement-membrane. Hence the false membranes 

 adhere more firmly to these, than to any other points in the 

 interior of the larynx. How often do we find, in making a post- 

 mortem examination, that the tracheal false membrane, continu- 

 ous with that of the laryngeal funnel, is quite loose as far up as 

 the rima glottidis, where it is firmly attached ; and we feel sure 

 that its spontaneous detachment at this point would have required 

 a very long time for its accomplishment. Yet it is just the true 

 chords Avhich are especially liable to become inflamed, while the 

 ventricle of Morgagni, for instance, is hardly ever affected. From 

 an etiological point of view it seems to me very important to lay 

 stress upon the preference which the disease exhibits for the 

 prominent parts of the mucous membrane, while its recesses are, 

 for the most part, intact. It is as though the pharynx had been 

 lightly brushed over with some corrosive agent, or as thougli 

 some irritant gas had been retained for a short while in the 

 upper part of the respiratory passages. 



