MECHANICAL PHENOMENA. 39 



When the pylorus relaxes the food is squirted for a con- 

 siderable distance along the duodenum (Fig. 13), where it lies 

 quietly until added to by further contributions from the 

 stomach. In this way a long thin string of food is formed. 

 During all this time the pancreatic and bile ducts pour the 

 secretions from their respective organs into the food. All at 

 once the string of food breaks up into several segments, and 

 the process of rhythmic segmenta* 

 tion already described 'above is 



started. After this has continued for o 

 some minutes the segments unite 

 into a single large mass, or into FIG. 13. 

 groups, and slowly pass along the (Copied from CANNON: 

 gut. Near the pylorus the peristalsis Am encan Journal of 

 . , * , . Al Physiology, 1902, VI, 



is more rapid than lower down in the ^2 ) 



small intestine. "The masses once 



started go flying along, turning curves, whisking hither and 

 thither in the loops, moving swiftly and continuously for- 

 ward." 1 After passing forward in this way for some dis- 

 tance the food is collected again into thick and long strings 

 and the process of segmentation repeated, The strings 

 of food may remain lying quietly in a loop of intestine 

 for an hour or more. During the first stages of digestion the 

 food lies chiefly on the right side of the abdomen, during^ the 

 later stages chiefly on the left. By these combined move- 

 ments of segmentation and peristaltic advance, both of which 

 are repeated from time to time, the food is finally brought to 

 the ileocsecal valve. 



The time elapsing before the food enters the duodenum 

 from the stomach varies, as already pointed out, with 

 the nature of the food. In general it may be said that no 

 food enters the small intestine until one or one and a half 

 hours after eating. Five to six hours elapse after eating 

 before food begins to appear in the large intestine, so that it 



1 CANNON: American Journal of Physiology, 1902, VI, p. 263. 



