DIGESTION IN THE LARGE INTESTINE. 251 



passed into the intestine is limited and the power of the intes- 

 tine not overtaxed. Later, the acidity is neutralized by the bile 

 and pancreatic juice, and the free acid in the stomach causes 

 a relaxation of the sphincter and another portion of the stomach- 

 contents enters the small intestine. Cannon states that the manner 

 in which the food is mixed with the digestive secretions, exposed 

 to the absorbing wall, and carried forward in the small intestine is 

 considerably different from the process observed in the large in- 

 testine and in the stomach. To the admirable process by which 

 these functions are performed in the small intestine he has given the 

 name " rhythmic segmentation." This activity of the muscular 

 wall is first seen in the duodenum when a mass of food has accu- 

 mulated there after repeated relaxations of the pylorus. The mass 

 of food is observed at first to be wholly quiet. Suddenly irregular 

 movements take place about it, and then at regular intervals along 

 its length constrictions of the circular musculature separate the 

 mass into a number of segments of equal size. Hardly have the 

 constrictions thus taken place when similar constrictions begin to 

 appear about the middle of each segment. As these new constric- 

 tions deepen, the first constrictions begin to relax. Finally, when 

 the new constrictions have completely divided the segments, the 

 first constrictions have entirely relaxed and the neighboring halves 

 of the divided segments unite to form new segments in the region 

 of the first constriction. Now these new segments are again divided 

 by circular constrictions about their middle, and neighboring halves 

 of these divided segments unite to make a third series, and so on. 

 This process of rhythmic segmentation of the food may go on for 

 several minutes in the duodenum (at the rate of thirty divisions 

 per minute in the cat), so that the food, coming from the stomach, 

 becomes thoroughly mixed with the out-pouring secretions of the 

 liver and the pancreas. It is usual for the process to be brought 

 to an abrupt end in the duodenum by active peristalsis. A peri- 

 staltic wave forms behind the mass of food and sweeps it swiftly 

 forward through several coils of the intestine. 



The movements of the small intestine, like those of the stomach 

 (p. 208) and large intestine, are inhibited whenever the animal 

 experimented upon manifests signs of anxiety, rage, or distress. 



DIGESTION IN THE LARGE INTESTINE, 



Undoubtedly, the process of intestinal digestion, which is 

 mainly carried on in the small intestine, is continued to some 

 extent in the large intestine, as the conditions there existing are 

 favorable to a continuance of this process, but the enzymes, which 

 are the efficient agents, are those of the fluids which have come 

 with the food into the large intestine, the mucous membrane here 

 producing no enzymes with digestive powers. In studying the 

 process of absorption we shall see that, although the large intes- 



