308 A MANUAL OF PHYSIOLOGY 



be locally excited by direct stimulation of the muscular fibres, 

 are no longer propagated, and a bolus introduced into the intes- 

 tine remains at rest where it is placed. Some have interpreted 

 these facts as indicating that the pendulum movements are 

 myogenic in origin. But evidence has lately been obtained that, 

 although they are not reflex movements elicited by afferent 

 impulses from the mucous membrane, since they continue in 

 unaltered intensity, in isolated loops of intestine immersed in 

 Locke's solution (p. 139) after removal of both mucosa and sub- 

 mucosa, they are nevertheless dependent upon Auerbach's 

 plexus. For when the circular muscular coat is separated from 

 this plexus, the automatic movements of this coat are abolished, 

 although the excitability of the musculature to direct stimulation 

 is not affected. The longitudinal coat, which is still in connection 

 with Auerbach's plexus, goes on contracting spontaneously 

 (Magnus). Under certain conditions a movement of food or 

 secretions in the reverse of the normal direction can be set up 

 in the small intestine in the intact body, e.g., in the case of obstruc- 

 tion of the intestine leading to vomiting of its contents. But 

 this does not necessarily indicate a reversal of the normal direc- 

 tion of the peristalsis. Such a reversal, if it occurs at all, is not 

 easy to realize by artificial stimulation, and even when an anti- 

 peristaltic wave is apparently started it travels up the intestine 

 only for a short distance and then dies out. A third variety of 

 intestinal movement has sometimes been described, the so- 

 called ' peristaltic rush ' (Meltzer, etc.). It consists of a rapidly 

 moving peristaltic contraction, preceded by relaxation of a long 

 portion of the tube. Such a contraction may even sweep down 

 without pause from the duodenum to the end of the ileum. 



The movements of the large intestine differ from those of 

 the small mainly in the great frequency of antiperistalsis. This, 

 indeed, seems to be the usual movement of the transverse and 

 ascending colon. The antiperistalsis recurs in periods about 

 every fifteen minutes, and each period generally lasts about five 

 minutes. The constrictions, running towards the caecum, 

 thoroughly churn and mix the remnants of the food, a con- 

 siderable absorption of which may take place in the upper part 

 of the large intestine. Regurgitation into the ileum in man is 

 prevented partly by the oblique entry of the ileum through the 

 wall of the colon (so-called ileo-caecal valve), but essentially by 

 the tonic contraction of the ileo-colic sphincter. The sphincter 

 usually permits the passage of material only in the direction 

 from small to large intestine. But as an occasional phenomenon, 

 a reverse movement may occur. Thus food may actually pass 

 back through the ileo-colic sphincter into the small intestine 

 under the action of a long-continued and vigorous antiperistalsis, 

 and a this way a considerable portion of a bulky enema may be 



