1004 DIGESTION 



through the esophagus, and the second, by its gurgUng through the 

 cardiac orifice. 



Nervous Control of Deglutition. — The act of swallowing involves 

 the voluntary mechanisms of the mouth and pharynx, and the invol- 

 untary mechanism of the esophagus. Consequently, deglutition may 

 be treated as a reflex act which is evoked by the projection of the bolus 

 against the mucosa of the fauces and pharynx, regions which are in- 

 nervated, on the one hand, by the trigeminus and, on the other, by the 

 glossopharyngeus. Besides these normal ''pace-makers," this passage 

 also includes several other areas which upon mechanical stimulation 

 give rise to deglutition. ^ The afferent channels involved in this reflex 

 lie in the second division of the trigeminus, the glossopharyngeus 

 and the pharyngeal branches of the superior laryngeus, whereas the 

 center occupies a place in the upper part of the medulla oblongata. 

 The motor fibers are contained in the hypoglossal, facial, trigeminus, 

 and vagus nerves. 



This enumeration shows very clearly that the parts involved in 

 deglutition, are arranged segmentally, but the sensory and motor 

 nerves controlling them, are coordinated in so precise a manner that 

 no interruption can possibly result in the orderly progression of the 

 wave of contraction. Thus, Meltzer^ has shown that the peristaltic 

 wave does not require an integrity of the muscular tube so long as the 

 nervous mechanisms have not been interfered with, while Mosso^ 

 has proved that a ligature applied to the esophagus, does not block 

 this wave, provided the reflex circuits have not been broken. An 

 even more striking proof of the successive involvement of the different 

 segments of this membranous tube has been furnished by Mikulicz. 

 It concerns a man whose esophagus had been resected in part for the 

 removal of a carcinomatous growth. The lower segment of this tube 

 was made to open through a wound in the neck, the purpose of this 

 arrangement being to allow the food to reach the stomach in the normal 

 way. It was found, however, that its introduction through this open- 

 ing did not incite peristalsis, whereas it was moved onward immedi- 

 ately if the act of swallowing was instigated in the normal way by 

 the corresponding movements of the mouth parts. 



An interval of at least 1.0 second must intervene between the suc- 

 cessive acts of swallowing, otherwise certain inhibitor influences will 

 arise which effectively block the succeeding peristalsis. This 

 inhibition is said to be under the control of the glossopharyngeus, 

 because it is a well-known fact that the normal pace-maker of deglu- 

 tition is represented by the nucleus of this nerve. Evidently, this 

 refraction allows each act of deglutition to be completed before the 

 beginning of the next, although it may happen at times that new food 

 reaches the cardiac sphincter before the material swallowed previ- 



1 Kahn, Archiv fiir Physiol., 1903, Suppl., 386. 



2 Brit. Med. Jour., 1906. 



2 Moleschott's Untersuchungen, 1876. 



