STEICTUEE OF INTESTINE. 375 



occurrence. Once in the lumen of the bowel the point of 

 impaction is largely determined by the size of the stone, for 

 there is a gradual diminution in the calibre of the intestine from 

 the duodenum to the ileo-caecal valve. The ileo-csecal valve 

 itself may offer considerable resistance to the passage of a stone. 

 A stone in the colon may become impacted in the pelvic segment 

 or near the anus, the calibre of the pelvic colon and rectum 

 being much less than that of the upper portions of the large 

 bowel. Comparatively small stones may induce obstruction by 

 setting up spasm of the muscular coat of the bowel. A gall 

 stone by its weight may drag down the coil of small intestine 

 which contains it, and even be felt in the pouch of Douglas. 



Impaction is not the only way in which gall stones produce 

 obstruction. A volvulus may result from their presence in the 

 bowel. Adhesions of the gall bladder may obstruct the bowel 

 or the obstruction may be due to acute peritonitis. 



Cicatricial strictures of the intestine arise in various ways 

 Tuberculous ulcers tend to encircle the gut, and strictures 

 may result in the lower part of the ileum, where lymphoid 

 tissue is very abundant and tuberculous ulcers, consequently, 

 are commonest. Dysenteric ulcers frequently cause stricture. 

 Strictures are met with in the rectum, pelvic colon, and some- 

 times at the hepatic and splenic flexures, all of which are 

 positions in which the bowel wall presents sharp bends. Cicatrices 

 may also occur in those parts of the bowel which have been 

 strangled in hernial orifices. 



Compression by adhesions usually affects those segments of 

 the intestine which are the least movable, such as the ascending 

 and descending colon and the hepatic and splenic flexures. 



CONGENITAL OBSTRUCTIONS OF THE FOOD PASSAGES. 



Congenital occlusion of the oesophagus, gives rise to vomiting, 

 choking, inanition, and hunger in the new born. The obstruction 

 cannot be due to a failure of the oral depression to meet the 

 anterior end of the primitive gut, for it lies below the pharynx, 



