FOOD AND DIGESTION 53 



duodenum, where the reaction is alkaline and where in- 

 testinal digestion begins. Finally undigested arid indi- 

 gestible articles are allowed to pass. 



Intestinal Movements. The muscular coats of the in- 

 testine are arranged in two layers, an outer longitudinal 

 and an inner circular. Obviously if each band of circu- 

 lar fibers contracted in succession a wave of constriction 

 would finally pass over the entire length of the tube 

 from stomach to large intestine; and, if each band re- 

 laxed directly after contraction, there would be an in- 

 active or dilated area always both above and below the 

 wave of contraction the dilated area above constantly 

 increasing and the one below decreasing in length. This 

 is the normal or peristaltic movement of the intestine. 

 At the same time the longitudinal fibers seem to con- 

 tract and draw the entire tube over the advancing food. 

 If, from disease or other cause, a wave can be excited 

 below and made to pass upwards, the contents of the in- 

 testine w r ould be forced into the stomach, as in obstruc- 

 tion of the bowel when fecal vomiting is seen. This ac- 

 tion is termed antiperistalsis. There seem to be local 

 constrictions at various points, in addition to normal peri- 

 stalsis, which serve to break the column of food into 

 many segments and both promote mixing with the in- 

 testinal and pancreatic ferments and exposure to ab- 

 sorptive channels. 



Nervous Control. Both the stomach and intestines re- 

 ceive nerve fibers through the vagi (pneumogastric or 

 tenth cranial nerve) and the sympathetic system of 

 nerves. 



Movements of Large Intestines. The opening of the 

 small intestine into the large is guarded by the ileocecal 

 valve and by a sphincter muscle, normally in a state of 

 contraction. Food passing into the large intestine is 



