33<> DIGESTION 



mechanism. The pendulum movements are, if anything, increased 

 in intensity and made more regular. But the peristaltic waves, 

 although they can be locally excited by direct stimulation of the 

 muscular fibres, are no longer propagated, and a bolus introduced 

 into the intestine 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 in- 

 tensity, in isolated loops of intestine immersed in Ringer's (or 

 Locke's) solution (p. 66) 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 spon- 

 taneously (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- 

 Fi g . 152. Intestine Segment beating tion o f the intestine leading to 



in Ringer's Solution. At 6 the oxy- vomiting of its Contents. But this 

 gen stream was increased. To be does not necessarily indicate a re- 

 read from left to right. Time trace, , , ,, J , .. ,. . 



half-minutes. (Reduced to one -half.) versal of the normal direction of 



the peristalsis. Such a reversal, 



if it occurs at all, is not easy to realize by artificial stimulation, and 

 even when an antiperistaltic 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 considerable absorption of which 

 may take place in the upper part of the large intestine. Regurgita- 

 tion into the ileum in man is prevented partly by the oblique entry 



