MECHANICAL PHENOMENA. 41 



10. The Nervous Control of the Alimentary Tract. We 



are still far from a correct understanding of the relation of 

 the nervous system to the movements of the various parts 

 of the alimentary tract. The experimental results obtained 

 by the score of investigators who have busied themselves 

 with this problem do anything but harmonize, a fact not 

 strange when the difficulties standing in the way of the 

 solution of the problem are considered. Narcotics, operative 

 procedures, etc., all so markedly influence the movements 

 of the alimentary tract that when these constitute the neces- 

 sary means which must be utilized in a study of the problem 

 uniform results can scarcely be expected. The following 

 paragraphs follow in the main STARLING'S 1 recent review of 

 the subject. 



The act of deglutition is only in part voluntary, and may 

 as a whole be considered as an essentially reflex act. The* 

 reflex is initiated whenever the palatine branches of the tri- 

 facial, the gloeso-pharyngeal, and superior laryngeal nerves 

 are stimulated either through the presence of food or saliva 

 in the mouth or by artificial means as when an electrical 

 stimulus is applied to the central end of the divided superior 

 laryngeal nerve. The afferent nerves pass into the medulla, 

 in the upper portion of which is situated a "centre?' whose 

 destruction is associated with impairment or total loss of the 

 power to swallow. The impulses which go to bring about a 

 movement of the muscles concerned in the act of swallowing 

 leave the medulla chiefly by way of the trifacial, facial, 

 and glosso-pharyngeaL The oesophagus is supplied almost 

 solely by the vagus. 



The oesophagus has the power of spontaneous peristaltic 

 contractions, within the body, however, the waves which 

 pass over the oesophagus in the ordinary act of swallowing 

 seem to be intimately connected with an uninjured nervous 

 system. Division of the nerves supplying the oesophagus 



f 

 1 STARLING: Ergebnfsse der Physiologie, 1902, 1, 2te Abth., p. 446. 



