54 PHYSIOLOGY FOR NURSES 



still in a semifluid state, but becomes solid about the 

 middle of the transverse colon. Waves of contraction 

 of the same general character as those seen in the small 

 intestine determine the onward movement in the large. 

 There seems to be a normal antiperistaltic Avave from 

 the middle of the transverse colon back to the ileocecal 

 valve to retard movement and allow longer time for ab- 

 sorption. Beyond the transverse colon we can properly 

 speak of feces instead of food. The material continues to 

 lose water until the sigmoid flexure is reacned. This is a 

 sort of reservoir for fecal matter where it remains until 

 just before defecation, the rectum apparently remain- 

 ing empty until that time. 



Defecation. This is partly a voluntary and partly an 

 involuntary act. The normal stimulus seems to be the 

 passing of fecal matter from the signioid into the rec- 

 tum. This excites the center for defecation in the lum- 

 bar part of the spinal cord, the sphincters of the rectum, 

 only partly under the control of the will, are relaxed, 

 the diaphragm contracts drawing a full supply ot air 

 into the lungs, and remains fixed while the abdominal 

 muscles contract forcibly and force out the contents of 

 the bowel. 



Vomiting 1 , Vomiting is the ejection of the contents 

 of the stomach through the esophagus and mouth. The 

 order of events is, a feeling of nausea, a flow of saliva, a 

 contraction of the stomach from the middle towards the 

 esophageal opening, descent of the diaphragm so as to 

 press on the stomach, a sudden and violent contraction 

 of the abdominal muscles, exerting still further pres- 

 sure on the stomach whose contents are forced along the 

 esophagus and out of the mouth. As the soft palate 

 can not be so well carried over the posterior nares from 



