504 



DIGESTION 



colon, where they collect chiefly in the sigmoid flexure. The descending 

 colon itself is never distended with contents and merely serves as a tube 

 for transferring the masses from the transverse colon to the sigmoid 

 flexure. The time taken for a capsule of bismuth to reach the various 

 parts of the large intestine is shown in Fig. 165. 



After a certain mass has collected in the sigmoid flexure and rectum, 

 the increasing distention causes a reflex evacuation of this portion of the 

 gut through centers located in the spinal cord. The impulses from these 

 centers, besides contracting the rectum, etc., also coordinate the contrac- 

 tion of the abdominal muscles and the relaxation of the sphincter ani 

 so as to bring about the act of defecation. By the skiagraphic method it 



Fig. 165. Diagram of time it takes for a capsule containing bismuth to reach the various parts 



of the large intestine. 



has been found that the pelvic colon gradually becomes filled with feces 

 from below upward, and-that the rectum remains empty until just before 

 defecation. 



EFFECT OF CLINICAL CONDITIONS ON THE MOVEMENTS 



Observations of practical value have been made on the behavior of the 

 peristaltic wave after various intestinal operations. After an end-to-end 

 anastomosis of the gut, no evidence can be obtained by the x-ray method 

 that any hesitation occurs in the movement of the shadows at the anas- 

 tomosis. On the other hand, when a lateral anastomosis is established, 

 stagnation of the food in the region of the junction may occur, this 

 having been found, on opening the gut, to be caused by the accumu- 



