350 FOOD AND DIGESTION 



from above downward. Such constrictions carry the intestinal contents 

 forward. The longitudinal muscles by their contraction produce pendular 

 motion of the intestine. 



A most instructive contribution to the knowledge of intestinal movements 

 has been made by Cannon. He fed cats food mixed with 10 to 33 per cent of 

 subnitrate of bismuth, and observed the shadows of the food when subjected 

 to the Roentgen rays. A length of food in the intestine was seen to be con- 

 stricted into a series of oval masses, figure 277. Each of these oval masses is 

 quickly constricted in the middle, and neighboring halves of adjacent masses 

 flow together. After this process is repeated a number of times a peristaltic 

 wave of the type previously described sweeps the whole content of the loop 

 down the intestinal tract. 



Peristaltic contractions of the same general type as in the small intestine 

 also occur in the large intestine. Cannon has noted a variation here, also. The 

 ascending and the transverse loops of the colon exhibit rhythmic antiperistalses 

 which keep the content moving against the ileocecal valve for several minutes 

 at a time. From time to time strong general contractions, in the cecum and 

 ascending colon, force some of the food onward. When material has accumu- 

 lated in the transverse colon, deep successive tonic constrictions appear and 

 force its contents into the descending colon. When sufficient material has ac- 

 cumulated here, it is evacuated by strong peristalses combined with compres- 

 sion by the contracting abdominal muscles. 



Reverse or antiperistalsis does not commonly occur in the small intestine, 

 but large nutrient enemata introduced into the rectum and colon may be forced 

 by antiperistaltic waves in the large intestine to and through the ileocecal 

 valve into the small intestine. Here they are treated in the same way as food 

 which has been introduced in the normal way. 



Influence of the Nervous System on Intestinal Peristalsis. As in 

 the case of the esophagus and stomach, the peristaltic movements of the in- 

 testines may be directly set up in the muscular fibers by the presence of food 

 acting as the stimulus. Few or no movements occur when the intestines are 

 empty. The intestines are connected with the central nervous system both 

 by the vagi and by the splanchnic nerves, as well as by other branches of the 

 sympathetic which come to them from the celiac and other abdominal plexuses. 

 The relations of these nerves respectively to the movements of the intestine 

 and the secretions are probably the same as in the case of the stomach already 

 considered. 



The vagus fibers are described as the motor fibers for the intestine, while 

 the sympathetic are said to be at least in part inhibitory. Various states of the 

 central nervous system, such as fear, anger, etc., inhibit the intestinal move- 

 ments. The intestine carries out peristalses when isolated from the body so 

 that the central connections do not originate, but are only regulative. The 

 intestinal movements are essentially automatic, depending on the rhyth- 



