THE RHYTHMIC AND PERISTALTIC MOVEMENTS 115 



of tone in the muscle in combination with a stretching of the 

 muscle due to the presence of food, just as is seen in other rhyth- 

 .mic organs such as the heart, where the stretching of a muscle 

 possessing tone causes rhythmic contractions. If the muscle of 

 the stomach is flabby and without tone, the rhythmic contrac- 

 tions cannot take place, even if its walls are stretched. Stimu- 

 lation of the vagus nerve causes a tonic condition of the 

 muscle, and then the rhythmic contractions take place upon 

 distension. These rhythmic contractions are not confined to 

 their place of origin but travel as waves of peristalsis, because 

 each contraction causes a distension of the adjacent muscle, which 

 although not in so extreme a condition of tone as at the band, is 

 still in a condition of tone sufficient to react when distended. 

 This travelling of a peristaltic wave is not dependent upon the 

 integrity of either the nervous or muscular coats in the intestine, 

 for Cannon has shown that, after one or more circular incisions 

 round the stomach down to the submucous layer, after the animal 

 has recovered from the operation, the peristaltic wave travels as 

 easily as before the operation. It is not due therefore to any 

 reflex nervous action through Auerbach's plexus but to the conse- 

 cutive stretching of the walls of the antrum, the muscles of which 

 are in a condition of tone. 



There is another normal peristaltic movement of a similar 

 character described by Elliott and Barclay-Smith in the large 

 intestine, where the contents undergo a churning and squeezing 

 action somewhat similar to what occurs in the antrum of the 

 stomach. Here also a tonic band of constriction is seen to be 

 formed always at the anal end of the proximal portion of the 

 colon at a varying distance from the anus, from which rhythmic 

 contractions arise and give origin to a series of peristaltic waves 

 which travel in the direction of the caecum. These anti-peris- 

 taltic waves depend upon a condition of tone, and are due to 

 the distension of the tonically contracted muscle just as in the 

 stomach. These two normally occurring peristaltic waves are de- 

 pendent upon the nervous system of Auerbach's plexus only in so 

 far as the nerve cells keep the muscle in a condition of tone. In 

 neither case are they abolished by nicotine, and in neither case 

 is the peristaltic or anti-peristaltic wave preceded by a wave of 

 inhibition. 



The ordinary peristaltic movements, in both small and large 



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