286 DIGESTION 



C. VOMITING 



Vomiting is an abnormal process by which the stomach contents are emp- 

 tied through the cardia instead of through the pylorus. Several muscles are 

 concerned in vomiting, but chiefly those of the diaphragm and abdomen. 

 These contract all at once, producing a high intraabdominal pressure which 

 naturally takes effect on the stomach wall. When the cardia is closed vomiting 

 does not result. We know that this must be true because when simultaneous 

 contractions of the diaphragm and abdominal muscles take place under other 

 circumstances, for example in defecation, the stomach is not emptied through 

 the cardia. The stomach wall itself plays little part in the process, for the 

 entire stomach may be replaced by a swine's bladder and vomiting therefrom 

 may be produced (Magendie). And yet it must be observed that the pyloric 

 portion of the stomach contracts powerfully' in vomiting and expels its con- 

 tents into the fundus. 



In vomiting the larynx and nasal passages are protected in the same way 

 as in swallowing, and the mass of stomach contents ejected from the stomach 

 under high pressure must therefore take its way through the mouth. The tongue 

 is not raised as in swallowing, but is pressed down and held out in the form 

 of a groove. 



Vomiting is induced either by certain drugs or by reflexes set up from the 

 base of the tongue, the throat, the stomach or the uterus. It may be caused also 

 even by the imagination or sight of something nauseating, or by excessive dis- 

 turbances of the brain. 



As appears from the foregoing, a large number of muscles cooperate in the 

 act of vomiting in a perfectly definite manner, and our current views of the 

 action of the central nervous system make it very probable that this coordina- 

 tion is obtained by a special center (the vomiting center). In fact it is stated 

 that in the dog the destruction of an area lying in the midline of the medulla 

 in the region of the calamus scriptorius prevents vomiting i. e., that this place 

 is the vomiting' center. This center is bilateral and lies in the deep layers of 

 the medulla (Tumas). Whatever the facts as to the actual presence of such a 

 center, this much appears certain, that the vomiting center and respiratory cen- 

 ter are not identical, as has often been assumed. For while certain respiratory 

 muscles take part in vomiting, many other movements supervene which have 

 nothing to do with respiration. Besides, simultaneous inspiratory contraction of 

 the diaphragm and expiratory contraction of the abdominal muscles never takes 

 place in respiration. 



5. MOVEMENTS OF THE INTESTINE 



The purpose of the intestinal movements is to mix thoroughly the contents 

 of this division of the alimentary canal with the digestive fluids poured into 

 its cavity, and to move the contents gradually along in the direction of the 

 anus. 



According to Griitzner, antiperistaltic contractions occur normally in the 

 intestine, by which the intestinal contents may be driven upward for some 

 distance. 



In the fasting state the intestine appears as a rule to be quiet. But about 

 one-quarter hour after eating it begins to move. These movements are induced 



