THE MECHANICAL FACTORS OF DIGESTION 411 



paralysis. The paralysis, however, passes off after a time in the non- 

 striated part of the oesophagus, which is endowed with the property 

 of performing peristaltic movements by virtue of its intrinsic nervous 

 mechanism: a secondary " lower " reflex mechanism, dependent upon 

 the nerve plexuses in the wall of the oesophagus. By this 

 mechanism, the presence of the bolus in the oesophagus itself causes 

 contractions, which push it onward towards the stomach. Nor- 

 mally this mechanism probably plays little or no part, the peri- 

 staltic movements being controlled reflexly through the vagus nerve. 

 After the oesophagus has been divided in an animal under moderate or 

 light anaesthesia, a swallowing movement initiated in the upper seg- 

 ment is followed by a movement in the lower segment. The peri- 

 staltic wave of the latter must in this case be excited and co-ordinated 

 reflexly through the central nervous system. In deep anaesthesia, how- 

 ever, this reflex propagation of the peristaltic wave may be abolished, 

 und a wave of peristalsis initiated in the upper segment of a divided 



FIG. 203. TRACINGS OF THE SHADOWS OF THE CONTENTS OF THE STOMACH AND 

 INTESTINES (CAT'S) MADE Two HOURS AFTER FEEDING (.4) WITH BOILED LEAN 

 BEEF, (B) WITH BOILED RICE. (Cannon.) 



or ligated oesophagus is not passed beyond the point of interruption. 

 We conclude, then, that normally the contraction of the oesophagus 

 is a part of the series of reflex nervous discharges initiated in the 

 " swallowing centre " by the stimulation of the afferent fibres. 



The Movements of the Stomach. The movements of the stomach 

 are adapted to the functions of its different parts. By the X-ray 

 method it is seen that the fundus, or reservoir, is practically devoid 

 of movement. It exerts a tonic grasp on its contents, which tend 

 to press them onwards whenever opportunity arises. Peristaltic 

 waves arise from the middle of the stomach (1 to 6, Fig. 199), and 

 pass in succession towards the pylorus. As food becomes discharged 

 into the intestine, the circular muscle becomes tonically contracted 

 so as to give a tubular form to the middle region, along which 

 the peristaltic waves continue to pass. The contents of the fundus 

 are thus gradually passed into the pylorus, and eventually the shadow 

 of the fundus disappears (5, 6, 7, Fig. 200). The regular, wave-like 

 contractions which pass over the pyloric end deepen as they go, and 



