These constrictions passing backward over the colon do not force the normal contents back through the valve into the small intestine again. I have seen hundreds of such constrictions, and only twice have there been exceptions to this rule,--once under normal conditions, when a small mass slipped back into the ileum, and at another time when a large amount of water had been introduced into the colon. The importance of the competence of the ileocæcal valve is now apparent; indeed, antiperistalsis in the colon gives new meaning and value to the location of a valve at the opening of the ileum. For, inasmuch as the valve is normally competent, the constrictions repeatedly coursing towards it force the food before them into a blind sac. The effect on the food must be the same as the effect seen in the stomach when the pylorus remains closed before the advancing waves. The food is pressed forward by the approach of each constriction; but since it cannot go onward in the blind sac, and is, moreover, subjected to increasing pressure as the constriction comes nearer, it is forced into the only way of escape, _i. e._, away from the cæcum through the advancing constricted ring. About twenty-five waves affect every particle of food in the colon in this manner during each normal period of antiperistalsis. The result must be again a thorough mixing of the contents and a bringing of these contents into close contact with the absorbing wall--a process which has already been variously repeated many times in the stomach and in the small intestine.