THE MECHANICAL FACTORS OF DIGESTION 417 



ment, passing over the entire length of intestine in about a minute, 

 and tending to void it of its contents (so-called " rushing peristalsis "). 

 " True peristalsis " involves a contraction of the gut above the 

 contents, and a relaxation below them (Fig. 213). To study this, a small 

 balloon may be introduced into the gut, and connected with a recording 

 tambour. The animal is immersed in a bath of warm Ringer's solution 

 before exposure of the gut. A stimulus applied locally above a bolus 

 introduced into the gut will cause relaxation of the wall in the region 

 of the bolus, whereas pinching below the bolus induces a strong con- 

 traction of the gut upon the bolus itself. Peristalsis is dependent 

 upon the local nervous mechanism of the small intestine, and is 

 abolished by painting the wall with cocaine or nicotine. It con- 

 tinues, however, Avhen all connections with the central nervous 

 system are destroyed (Fig. 214). 



PIG. 213. DIAGRAM SHOWING PERI- 

 STALTIC CONTRACTION OF INTESTINE. 



~Fia. 214. PHOTOGRAPH OF A PERI- 

 STALTIC WAVE OF SMALL INTESTINE 

 PUSHING MATERIAL INTO THE COLON. 

 (Cannon.) 



* Peristaltic rush " is probably of the nature of true peristalsis, 

 and occurs particularly when it is necessary to rid the gut of irritating 

 substances. It is usually stated that antiperistalsis does not occur 

 in the small intestine, and, so far, has not been observed, but clinical 

 evidence points to the fact that it occurs. For instance, nutrient 

 enemata containing egg administered per rectum have been observed 

 shortly afterwards flowing from a duodenal fistula. In cases of 

 intestinal obstruction, also, the vomit may become of a faecal nature 

 so-called " faecal vomiting." 



The movements of the small intestine are affeoted by the vagus 

 and sympathetic nerves. Peripheral stimulation of the vagus causes 

 an initial inhibition of the whole small gut, followed by increased 

 contractions. Stimulation of the splanchnic nerves causes inhibition 

 of the movements, with relaxation of both muscular coats. The 

 splanchnics probably exert a tonic inhibitory influence, which may 

 become excessive in abdominal and nervous disorders. The time 

 usually occupied by the food in traversing the 22 feet of small 

 intestine is about six ho^rs. 



27 



