396 FOOD AND DIGESTION 



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, vigorous contractions when filled. 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 re- 

 spectively to the movements of the intestine and the secretions are probably 

 the same as in the case of the stomach already considered. 



The vagus carries the motor fibers for the intestine, while the sympathetics 

 are inhibitory. Various states of the central nervous system, such as fear, 

 anger, etc., inhibit the intestinal movements. The intestine, and stomach, 

 too, carries out peristalses when isolated from the central nervous sys- 

 tem and indeed from the body, so that the central connections do not originate 

 the rhythmic stimulus but are only regulative. The intestinal movements 

 are essentially automatic. It has long been known that isolated portions 

 of the intestine contract rhythmically and automatically. This has been 

 proven for both the longitudinal and circular muscles, and in the absence 

 of the mucous membrane. According to Magnus, rhythmic contractions 

 do not occur in the muscle if the plexus of Auerbach be removed. He con- 

 cludes that the automatic rhythm is inherent in the local nerve ganglia, 

 that it is not a reflex since it occurs in the absence of the mucosa, and that 

 the contractions of the smooth muscles are directly dependent upon the local 

 nerve distribution. Others contend that the contractions are independent, 

 depending on the rhythmic property of the muscle itself, but co-ordinated 

 by the complex local nervous mechanism. By either conception the nerve 

 connections with the central nervous system are regulative and co-ordinative. 



The innervation of the large intestine is also double in character and 

 the relations are doubtless the same as in the small intestine. 



Defecation. The emptying of the bowels is essentially an involuntary 

 act which has acquired a certain amount of voluntary regulation. The 

 act is accomplished wholly reflexly in dogs with isolated lumbar cord, in 

 fact has been observed when the lumbar spinal cord was removed. In 

 the latter case defecation occurs by automatic peristalsis of the rectum, and 

 colon, while in the former reflexes through the lumbar cord carry out the 

 act. When the material that has accumulated in the colon descends into 

 the rectum, which is normally empty, it initiates the reflex stimulus which 

 culminates in opening the bowel, or defecation. Hertz and others have 

 taken X-ray photographs of the human immediately before and after open- 

 ing the bowels, with a view to a better understanding of what structures 

 take part in the process. It is found that the entire colon as far back as the 

 ilio-cecal sphincter may be emptied during the act, see figure 2760. 



