MOVEMENTS OF THE INTESTINES 823 



account of the movements as they probably occur in man. They 

 agree very closely with those observed by Cannon under normal 

 circumstances in the cat by means of the Rontgen rays. The food 

 as it passes from the ileum first fills up the proximal colon. The 

 effect of this distension is to cause a contraction of the muscular 

 wall at the junction between the ascending and transverse colon. 

 This contraction travels slowly over the tube in a backward direction 

 towards the caecum, and is quickly succeeded by another, so that 

 the colon may present at the same time several of these advancing 

 waves. These waves are spoken of as anti-peristaltic ; but as they 

 do not involve also an advancing wave of inhibition, they must not 

 be regarded as representing the exact antithesis of a peristaltic wave, 

 as we have defined it. The effect of these waves is to force the food 

 up into the caecum, regurgitation into the ileum being prevented 

 partly by the obliquity of the opening, partly by the tonic contraction 

 of the ileocolic sphincter. As the whole of the contents cannot 

 escape into the caecum, a certain portion will slip back in the axis 

 of the tube, so that these movements have the same effect as the 

 similar contractions in the pyloric end of the stomach, causing a 

 thorough churning up of the contents and its close contact with 

 the intestinal wall. The movements are rendered still more effective 

 by the sacculation of the walls of this part of the large intestine. 

 The distension of the caecum caused by this anti-peristalsis excites 

 occasionally a true co-ordinated peristaltic wave, which, starting 

 in the caecum, drives the food down the intestine into the transverse 

 part. These waves die away before they reach the end of the colon, 

 and the food is driven back again by waves of anti-peristalsis. 

 Occasionally more food escapes through the ileocolic sphincter from 

 the ileum, so that the whole ascending and transverse colon may be 

 filled with the mass undergoing a constant kneading and mixing 

 process. The result of this process is the absorption of the greater 

 part of the water of the intestinal contents, as well as of any nutrient 

 material, and the drier part of the intestinal mass collects towards 

 the splenic flexure, where it may be separated by transverse waves 

 of constriction from the more fluid parts which are being driven to 

 and fro in the proximal and intermediate portions. By means of 

 occasional peristaltic waves these hard masses are driven into the 

 distal part of the colon. The distal colon must be regarded as a 

 place for the storage of the faeces and as the organ of defaecation. 

 In the transverse colon, in the descending and ileo-colon, the anti- 

 peristaltic movements and consequent churning of the contents 

 are probably slight. These therefore represent the intermediate 

 colon, with propulsive peristalsis as its chief activity. The descend- 

 ing colon is never distended, and Elliott therefore regarded it as a 



