820 PHYSIOLOGY 



a direct irritating effect on the wall of the gut (Fig. 343). In this case 

 the contraction above and the inhibition below cause an onward 

 movement of the bolus, which travels slowly down the whole length 

 of the gut until it passes through the ileocsecal opening into the 

 large intestine. The peristaltic contraction involves the co-operation 

 of a nervous system. Whereas in the oesophagus it is the central 

 nervous system which is involved, the peristaltic contractions in 

 the small intestine occur after severance of all connection with the 

 brain and spinal cord. On the other hand, they are absolutely abolished 

 by painting the intestine with nicotine or with cocaine. They must 

 therefore 'be ascribed to the local nervous system contained in 

 Auerbach's plexus, which we can regard as a lowly organised nervous 



FIG. 343. Passage of bolus. Contractions of longitudinal coat (enterograph). 

 The bolus (of soap and cotton-wool) was inserted into the intestine four 

 inches above the recorded spot at A. The figures below the tracing indicate 

 the distance of the middle of the bolus from the recording levers As the bolus 

 arrived two inches above the levers there is cessation of the rhythmic contrac- 

 tions and inhibition of the tone of the muscle. This is followed, as the bolus is 

 forced past, by a strong contraction in the rear of the bolus. 



system with practically one reaction, namely, that formulated above 

 as the c law of the intestines.' An anti-peristalsis is never observed 

 in the small intestine. Mall has shown that, if a short length of gut 

 be cut out and reinserted in the opposite direction, a species of 

 partial obstruction results, in consequence of the fact that the peri- 

 staltic waves, started above the point of operation, cannot travel 

 downwards over the reversed length of gut. The intestine above 

 this point therefore becomes dilated. If, however, the reactions 

 of the local nervous system be paralysed or inhibited, a reflux of 

 intestinal contents is quite possible, since the contractions excited 

 at any spot by local stimulation of the muscle have the effect of 

 driving the food either upwards or downwards ; the direction of 

 movement of the food will be that of least resistance. 



The movements of the small intestine are also subject to the 

 central nervous system. Stimulation of the vagus has the effect of 

 producing an initial inhibition of the whole small intestine, followed 



