374 DEGLUTITION. [BOOK n. 



ment of the back part of the tongue inay be sufficient not merely 

 to introduce the food into the grasp of the constrictors of the 

 pharynx, but even to propel it rapidly, to 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. Deglu- 

 tition in this fashion still remains possible after these constrictors 

 have become paralysed by section of their motor nerves. 



When a second act of deglutition succeeds a first with sufficient 

 rapidity, the nervous changes which start the pharyngeal move- 

 ments of the second act appear to inhibit the cesophageal move- 

 ments 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 differ- 

 ent 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 peris- 

 taltic 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 respira- 

 tory orifice, and in consequence its passage again becomes compar- 

 atively 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 cesophageal 

 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, 

 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 exer- 



