RHYTHMIC SEGMENTATION 139 



vitiated by the drastic operative procedure involved. It 

 appears that secretin, as it influences the activity of the 

 liver and the pancreas, influences also that of the upper 

 part of the intestine. During the course of digestion there 

 may be produced other hormones which cause secretion 

 in the lower part of the gut. 



A local secretion, produced through the agency of 

 Meissner's plexus, occurs whenever a sohd object touches 

 the intestinal mucosa. 



Movements of the Small Intestine 



The digesting mass does not occupy the whole length of 



, (T) (X) CD CD O O (S 

 3.o<i)CD®CDCD(5i^ 



Fig. 28. — Segmentation movements (Cannon). 



the intestine uniformly, but is grouped in segments of 

 varying length, the intervening sections of the gut being 

 practically empty. The food, after it has passed the pylorus, 

 lies quiescent in the duodenum, where, of course, it receives 

 the conjoint secretion of hver and pancreas. When by 

 later additions from the stomach a certain longth of gut is 

 thus occupied, this part of the intestine undergoes rhythmic 

 segmentation, the nature of which is best understood by 

 reference to the diagram. As seen by X-ray examination 

 after a bismuth meal, the continuous dark shadow suddenly 

 breaks up into a number of segments separated by clear 

 areas. After a few seconds, these segments as suddenly 



