376 



FOOD AND DIGESTION 



FIG. 263. Horizontal Section of a 

 Small Fragment of the Mucous Mem- 

 brane, including one entire crypt of 

 Lieberkuhn and parts of several others. 



Vomiting. The expulsion of the contents of the stomach in vomiting 

 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 surface 

 against which the stomach can be pressed. In this way as well as by 



its own contraction 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 actively dilated. The pylorus 

 is closed and, the stomach itself also con- 

 tracting, the action of the abdominal 

 muscles produces strong compression 

 which expels 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 pressure 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 the contraction 

 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 

 uvula, the intestine, etc. Vomiting may occur from stimulation of sensory 

 nerves from many organs, e.g., kidney, testicle, etc., or by impulses arising 

 in the organs of special sense, the eye, olfactory membrane, etc. The sensory 

 impulses are co-ordinated by a nerve center located in the medulla. The 

 center may also be stimulated by impressions from the cerebrum and cere- 

 bellum or by changes arising in the center itself, the so-called central vomiting 

 occurring in disease of those parts. The efferent impulses are carried by the 

 phrenics and other spinal nerves and by the vagus. 



DIGESTION IN THE INTESTINES. 



The food that enters the small intestine has already been subjected to two 

 digestive enzymes. The ptyalin of the saliva and the pepsin of the gastric 

 juice together with the mechanical processes involved have reduced the food 



