MOVEMENTS OF THE INTESTINES 395 



has been made by Cannon. He fed cats food mixed with 10 to 33 per cent, of 

 subnitrate of bismuth, and observed the shadows of the food when subjected 

 to the X-rays. A length of food in the intestine was seen to be constricted 

 into a series of oval masses, figure 277. Each of these oval masses is quickly 

 constricted in the middle, and neighboring halves of adjacent masses flow 

 together. After this process is repeated a number of times a peristaltic wave 

 of the type previously described sweeps the whole content of the loop down 

 the intestinal tract. The segmentations of the intestine are facilitated by 

 pressure from within, perhaps stimulated by the direct pressure of the food. 

 In general, hollow organs receive their most effective motor stimulus in this 

 manner, i.e., by distention. This rule applies in the lengths of the small 

 intestine. 



FIG. 277. Diagram Illustrating the Segmentation of the Food in the Small Intestine. 



(Cannon.) 



Peristaltic contractions of the same general type as in the small intestine 

 also occur in the large intestine. Cannon has noted a variation here also. 

 The ascending and the transverse loops of the colon sometimes exhibit 

 rhythmic antiperistalses which keep the content moving against the ilio- 

 cecal sphincter for several minutes at a time. In the meantime digesting 

 material is being received into the ascending colon through the ilio-cecal 

 sphincter, being slowly forced on by the peristalses of the lower loops of the 

 small intestine. From time to time strong general peristalses in the colon 

 slowly force the food onward. Under ordinary circumstances remnants 

 of unabsorbed material in the colon do not pass beyond the pelvic colon, be- 

 ing held at this point until the greater portion of the entire colon is moderately 

 filled. When sufficient material has accumulated here, it is evacuated by 

 strong peristalses combined with compression by the contracting abdominal 

 muscles. 



Reverse peristalsis, antiperistalsis, does not commonly occur in the small 

 intestine, but large nutrient enemata introduced into the rectum and colon 

 may be forced by antiperistaltic waves in the large intestine against the 

 ilio-cecal sphincter at a time when it is atonic and relaxed thus allowing 

 materials to pass through the ilio-cecal valve into the small intestine. In 

 normal healthy individuals this sphincter reacts, according to Hertz, like 

 the sphincter of the pylorus effectively closing the tube. 



