3i8 DIGESTION 



of the pharynx over the bolus by the action of the palato- and stylo- 

 pharyngei. 



The second or oesophageal portion of the involuntary stage is 

 a more leisurely performance. The bolus is carried along by a 

 peculiar ' peristaltic ' contraction of the muscular wall of the 

 oesophagus, which travels down as a wave, constricting the tube 

 and pushing the food before it. In front of the constricting wave 

 moves a wave of inhibition, so that the part of the oesophagus into 

 which the bolus is about to pass is always relaxed, while the part 

 behind it is contracted. This exact co-ordination of inhibition 

 and contraction is the essential thing in peristalsis. When the food 

 reaches the lower end of the gullet the tonic contraction of that part 

 of the tube is for a moment relaxed by reflex inhibition, and the 

 morsel passes into the stomach. Beaumont saw, in the case of 

 St. Martin, that the oesophageal orifice of the stomach contracted 

 firmly after each morsel was swallowed, and so did the gastric walls 

 in the neighbourhood of the fistula when food was introduced by 

 this opening. In the dog the whole process of swallowing from 

 mouth to stomach has been shown to occupy four to five seconds, 

 but the time is by no means constant. In man the peristaltic wave 

 requires about five to six seconds to travel from the level of the 

 glottis to the cardiac orifice. The rate of movement is greater in the 

 upper than in the lower portion of the oesophagus. 



Such is the mechanism of deglutition when the bolus is of such 

 consistence and size that it actually distends the oesophagus. But 

 it has been shown that liquid food is swallowed in a different way. 

 The food lying on the dorsum of the tongue, suddenly put under 

 pressure by the sharp contraction of the mylo-hyoid muscles, is 

 shot rapidly down to the lower part of the lax oesophagus, or, occa- 

 sionally, some of it even into the stomach. So far the process has 

 only occupied one-tenth of a second. After several seconds, the 

 food, or the portion which still remains in the oesophagus, is forced 

 through the cardiac sphincter into the stomach by the arrival of 

 the tardy peristaltic contraction of the oesophageal wall (Kronecker 

 and Meltzer). Two sounds may be heard in man on listening in 

 the region of the stomach or oesophagus during deglutition of liquids, 

 especially when, as generally happens, they are mixed with air. 

 The first sound occurs at once, and is due to the sudden squirt of 

 the liquid along the gullet ; the second, which is heard after a distinct 

 interval (about six seconds), is caused by the forcing of the fluid 

 through the cardiac orifice of the stomach by the contraction of the 

 oesophagus. 



There are certain peculiarities which distinguish this peristaltic 

 movement of the oesophagus from that of other parts of the alimen- 

 tary canal. It is far more closely related to the central nervous 

 system, and, unlike the peristaltic contraction of the intestine, can 



