34 



less frequently seen in the more advanced and very chronic stages. 

 The fact that it is most common in those bowels showing the pre- 

 ulcerative lesions speaks for its being intermediate between the 

 very early petechial lesions and the undermined ulcer. This is the 

 type most common in the ileum. 



(&) Classic or undermined ulcers. — These are seen in an early 

 stage, as minute yellowish or grayish spots in the mucosa of the 

 bowel, frequently at the centers of the petechise spoken of as the 

 preulcerative stage of the disease, and are usually surrounded by 

 a zone of congestion more or less well marked, as the case may be. 

 These spots represent the mouths, filled with necrotic material, of 

 passages leading to larger or smaller cavities in the submucosa, 

 which are also filled with the same material. As the process ex- 

 tends, the pocket in the submucosa is enlarged parallel with the 

 surface in all directions, and although the necrobiosis eventually 

 involves all the coats of the bowel, the muscular layers and the 

 mucous membranes suffer less rapidly, so that there results an ulcer 

 with its base on the circular muscle and with overhanging edges of 

 mucous membrane. Such ulcers may be of sizes varying from that 

 of a pinhead up to that of the palm of the hand, and may occur in 

 any part of the large intestine and even in the lower part of the 

 ileum, though in the latter they are smaller. 



During the process of ulceration, the submucosa becomes generally 

 thickened and oedematous, as may also the muscular layers and the 

 peritoneal coats. 



During extension, such ulcers may coalesce beneath or upon the 

 surface, and it is no rare thing to find even small submucous pouches 

 communicating with each other by tunnels, Avhile the mucous 

 membrane may show no more than a catarrhal condition. 



In many of the larger lessions, the circular muscle fibers are 

 exposed, forming the base of an ulcer, and shreds of this may be 

 seen nearly separated from the rest and may be removed by gently 

 scraping. In still more extensive ulceration the muscular laj'er may 

 become necrosed or even perforated and the ulcer may then be 

 bounded externally by the peritoneum or omentum. 



There are, perhaps, few diseases in wdiich the omentum plays so 

 imported a protective part as in the one under discussion. Very 

 early in the ulcerative stages this membrane may be found plastered 

 upon the peritoneal surface of the gut in preparation for the acci- 

 dents which may follow. 



