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A TEXTBOOK OF PHYSIOLOGY 



The ileo-colic sphincter is normally closed, but relaxes before an 

 advancing peristaltic wave, and admits the food into the large intes- 

 tine. Stimulation of the splanchnic nerve produces a strong contrac- 

 tion of this sphincter. Vagal stimulation has no effect on it. 



The Movements of the Large Intestine. The ileo-colic sphincter 

 opens before the wave of peristalsis when this reaches the terminal 

 part of the ileum, and the ileal contents are then passed on into the 

 large intestine. The first effect of their advent, observed by the 

 skiagraph method, is to bring about antiperistaltic movements of 

 the ascending colon. These start from the junction of the ascending 

 and transverse colon, and force the food down into the caecum, the 

 ileo-colic sphincter being now closed. The waves of antiperistalsis 

 occur at about the same rate as those of the stomach (five to six a 



R. 



FIG. 215. DIAGRAM TO SHOW THE HOURS WHICH ELAPSE AFTER A BISMUTH MEAL 

 BEFORE THE DIFFERENT PARTS OF THE COLON ARE REACHED. (Hurst.) 



minute), and the period of antiperistalsis lasts on an average about 

 four to five minutes, and recurs after varying lengths of time, generally 

 from ten to fifteen minutes. Antiperistalsis is the predominating 

 movement of the first part of the colon. As a result, the contents 

 are retained there for a considerable time, generally about two hours, 

 and the absorption of water is greatly facilitated. It is probable that 

 the arrival of new material in the large intestine pushes on the contents 

 beyond the antiperistaltic area, but it is possible that from time to 

 time a wave of true peristalsis helps to push on the contents into the 

 transverse colon. 



Thus far, true waves of antiperistalsis have not been observed 

 in man, but there is reason to think that such take place in him no 

 less than in animals. It is known that nutrient enemata are quickly 

 passed back into the ascending colon, and, when large, may pass 

 thence into the small intestine. 



