454 DEGLUTITION. [BOOK lu 



shoot it in fact, along the lax oesophagus before the muscles of that 

 organ have time to contract. In such a mode of swallowing the 

 middle and lower constrictors take little or no part in driving the 

 food onward, though they and the oesophagus appear to contract 

 from above downwards after the food has passed by them, as if to- 

 complete the .act and to ensure that nothing has been left behind. 

 Deglutition in this fashion still remains possible after these con- 

 strictors have become paralysed by section of their motor nerves. 



When a second act of deglutition succeeds a first with suffi- 

 cient rapidity, the nervous changes which start the pharyngeal 

 movements of the second act appear to inhibit the oesophageal 

 movements of the first act; and when swallowing is repeated 

 rapidly several times in succession, the oesophagus remains quiet 

 and lax during the whole time, until immediately after the last 

 swallow, when a peristaltic movement closes the series. 



When the stethoscope is applied over the oesophagus, at 

 different regions, a sound is heard during deglutition ; sometimes- 

 two sounds are heard. The first and most constant is coincident 

 with the passage of the bolus, and is due to this and to the 

 muscular sound of the contracting muscles. The later and less 

 constant sound appears to be caused by a quantity of air-bubbles 

 with which the bolus was entangled, lodged at the cardiac end of 

 the oesophagus, being forced into the stomach by the sequent 

 peristaltic contraction of the oesophagus. 



It will be seen, from what has been said, that deglutition, 

 though a continuous act, may be regarded as divided into three 

 stages. The first stage is the thrusting of the food through the 

 isthmus faucium ; this may be either of long or short duration. 

 The second stage is the passage through the upper part of the 

 pharynx. Here the food traverses a region common both to the 

 food and to respiration, and in consequence the movement is as 

 rapid as possible. The third stage is the descent through the 

 grasp of the constrictors. Here the food has passed the respi- 

 ratory orifice, and in consequence its passage again becomes com- 

 paratively slow, except in case of fluids and small morsels, 

 when, as we have seen, it may continue to be rapid. The passage 

 along the oesophagus may perhaps be regarded as constituting a 

 fourth stage ; but it will be more convenient to consider the 

 oesophageal movements by themselves. 



The first stage in this complicated process is undoubtedly a 

 voluntary act. The raising of the soft palate and the approxi- 

 mation of the posterior pillars may also be, at times, voluntary r 

 since they have been seen, in a case where the pharynx was laid 

 bare by an operation, to take place before the food had touched 

 these parts ; but the movement may take place without any 

 exercise of the will and in the absence of consciousness. Indeed the 

 second stage taken as a whole, though some of the earlier com- 

 ponent movements are, as it were, on the borderland between the 



