CONTRACTIONS AND CLOSURES OF THE INTESTINAL CANAL. 587 



are the most frequent. Cicatrization of tuberculous (scrofulous) ulcers 

 rarely, and of typhoid ulcers never, leads to stricture of the intestine. 

 Cicatricial strictures occur in the rectum also, after the healing of 

 syphilitic ulcers or of wounds. Simple stricture due to hypertrophy 

 of the walls of the intestine is more rare than that which occurs in the 

 oesophagus and pylorus from the same cause. Lastly, we must men- 

 tion those strictures induced by neoplasia, particularly carcinoma, of 

 which we shall hereafter speak. 



3. The intestine may be closed by rotation on its axis ; even half a 

 rotation closes its calibre. The closure may result either from a por- 

 tion of intestine rotating on its own axis, or from the mesentery, or 

 part of it with the intestine attached to it, being twisted on itself, or 

 from a portion of mesentery with its intestine being wound around 

 another loop of intestine. A long and relaxed mesentery predisposes 

 to the occurrence of rotation on the axis ; the mechanism of this is 

 obscure. 



4. Closure of the intestine may result from internal strangulation, 

 or incarceration. This occurs when a portion of intestine enters any 

 fissure in the abdomen, or gets behind a ligament stretched there, and 

 thus becomes constricted. A portion of intestine may be thus stran- 

 gulated in the foramen of Winslow, or in a congenital or developed 

 fissure in the omentum or mesentery. The bands which most fre- 

 quently cause strangulation are those resulting from peritonitis ; they 

 occur between the most different organs, but particularly between the 

 uterus and its surroundings. A portion of intestine may be thrown 

 around the omentum which is drawn downward strongly, or around 

 the vermiform process which has become adherent at its point, and 

 may thus be constricted. 



5. The intestine may be closed by one portion of intestine entering 

 another portion ; this almost always takes place from above downward. 

 This is called invagination, or intussusception, as it consists of an in- 

 version of the intestine into itself. When this occurs, there are three 

 layers of intestine, one over the other ; the outer one is called the 

 sheath, or intussuscipiens ; the middle and inner one are called the in- 

 tussusceptum. The mucous surface of the external and middle layers 

 and the serous coat of the middle and internal layers are brought in 

 apposition. The mesentery lies between the middle and internal lay- 

 ers. As this is attached at its root, it is rendered tense by this inver- 

 sion, and hence exercises traction where it is inserted into the intes- 

 tine. In consequence of this one-sided traction, the invaginated portion 

 of intestine is distorted ; its opening is drawn from the middle toward 

 the side of the sheath, and it is elongated to a narrow fissure. If there 

 be quantities of intestinal contents pressing downward, the invaginated 



