330 



FOOD AND DIGESTION 



bring about relaxation or dilatation. It is also demonstrated that afferent 

 vagus impulses influence the contractions in the stomach. 



It seems probable that automatic peristaltic contraction is inherent in the 

 muscular coat of the stomach, and that the central nervous system is only 

 employed to regulate it by impulses passing down by the vagi or splanchnic 

 nerves. 



Vomiting. The expulsion of the contents of the stomach in vomit- 

 ing is preceded by a deep inspiration with closure of the glottis, followed im- 

 mediately afterward by strong contractions of the muscles of the abdomen, 

 diaphragm, and stomach. The diaphragm forms an unyielding surf ace against 

 which the stomach can be pressed. In this way as well as by its own contrac- 

 tion the diaphragm is fixed, to use a technical phrase. At the same time the 

 cardiac sphincter muscle is relaxed, and the orifice which it naturally guards is 



FIG. 263. Horizontal Section of a Small Fragment of the Mucous Membrane, including one 

 entire crypt of Lieberkiihn and parts of several others. 



actively dilated. The pylorus is closed, and, the stomach itself also contracting, 

 ;he action of the abdominal muscles produces strong compression which ex- 

 pels the contents of the organ through the esophagus, pharynx, and mouth. 

 Reversed peristaltic action of the esophagus probably increases the effect. 



It has been frequently stated that the stomach itself is quite passive during 

 vomiting, and that the expulsion of its contents is effected solely by the pres- 

 sure exerted upon it when the capacity of the abdomen is diminished by the 

 contraction of the diaphragm. It is true that facts are wanting to demonstrate 

 with certainty this action of the stomach in vomiting; but cases of fistulous 

 opening into the organ appear to support the belief that it does take place; and 

 the analogy of the case of the stomach with that of the other hollow viscera, 

 as the rectum and bladder, may also be cited in confirmation. 



Vomiting is a reflex act. It can be excited by irritation of the lining of 

 the stomach which is perhaps the normal stimulus. It is excited by stimula- 

 tion or irritation of other parts of the alimentary tube, i.e., the pharynx, the 



