442 MUCOrS 3IEMBRANES. 



recovery caii only take place by expulsion of the necrosed pai'ts 

 and consequent ulceration. An increased degree of congestion 

 at tlie edges of the slough, is followed by suppuration, and detach- 

 ment of the dead part ; the latter continues, however, to hang on 

 for a long time to the base or edges of the ulcer, and acquires a 

 yellow, green, or brown tint, by contact with and imbibition of 

 bile-pigment. It finally comes away in shreds, leaving an ulcer 

 w-hose size is determined by that of the slough, and whose floor 

 is usually composed of the deepest layer of the submucous con- 

 nective tissue. In severe cases the ulcer penetrates still more 

 deeply, and the expulsion of the sequestrum coincides with per- 

 foration into the peritoneal cavity. In such cases we may infer 

 that the infiltration extended from the first, not only through the 

 entire thickness of the submucous tissue, but also through the 

 interstitial connective tissue of the muscular coat, to the sub- 

 serous and serous layers. 



The healing of these typhoid ulcers follows at once upon the 

 sequestrating inflammation. Xo sooner is the slough thrown ofi:', 

 than a small quantity of embryonic tissue springs up on the floor 

 of the ulcer : the precipitous abruptness of its edges is under- 

 mined by a colhquative softening ; the collapsed border over- 

 hangs a portion of the denuded floor, to which it speedily 

 becomes attached by cicatricial tissue ; the central part, which is 

 still naked, comes at a later period to form a smooth, lustrous 

 surface, with pigmented edges, on which neither villi, glands, 

 nor any of the other component elements of a mucous membrane, 

 are ever regenerated. By transmitted light, these patches appear 

 thin and transparent ; this is due to the absence of a mucous 

 layer. 



As regards the intestinal haemorrhages which occasionally 

 complicate abdominal typhus, it may be remarked that the 

 frequent, trifling, and harmless ones, occm' by diapedesis from 

 the over-congested edges of the ulcers ; the more severe bleed- 

 ings, from those larger vessels, wliich served at one time to con- 

 vey blood to the necrosed tissues, and which are now hable to be 

 torn, perhaps in consequence of premature detachment of the 

 sequestra by passing f^cal masses. 



§ 381. So much for the morbid changes in the mucous 

 membrane. In constant association with them, we find an affec- 

 tion of those mesenteric glands which draw their lymph from the 



