DIGESTION 



201 



a contraction of the circular fibers behind the mass of food and a relaxation 

 of the fibers in advance of it. The result is a movement forward of the food, 

 and as it moves it is followed by a ring of constriction and preceded by a 

 ring of relaxation or inhibition. The rate of movement of the peristaltic wave 

 is usually extremely slow except in the duodenal region where it is quite rapid. 



The first of these two movements to make its appearance is the peristaltic 

 which arises at the upper portion of the duodenum from which it sweeps 

 downward with considerable rapidity, carrying with it the food which has 

 been discharged from the stomach and which has accumulated in this region. 

 From the appearance, as shown by Rontgen ray examination, which the 

 extreme upper portion of the duodenum presents, before peristalsis arises 

 due to its distension by food, it has been designated the cap or pitieus 

 ventriculi. 



After the peristaltic wave has advanced the food a variable distance, it 

 disappears and the food comes to rest. By this procedure the incoming food 

 from the stomach is readily accommo- 

 dated in the duodenal portion of the in- 

 testine. With the disappearance of the 

 peristaltic wave, rhythmic segmentation 

 again arises in the portion of the intes- 

 tine corresponding to the new situation 

 of the segment of food. This in turn is 

 succeeded by another peristaltic wave 

 which advances the food to a more dis- 

 tant region of the intestine. This con- 

 tinues until at the end of gastric digestion 

 a more or less continuous column of food 



B 



FIG. 83. THE DIVISIVE OR SEGMENT- 

 ING MOVEMENTS OF THE SMALL INTESTINE. 

 A, surface of a portion of the intestine, 



Occupies the lumen of the small intestine showing six constrictions which divide the 



contents into five segments, as shown in 

 B: as these constrictions pass away new 

 ones come in between them and divide 



C. Repetition of this process results in tl 

 condition shown in D. (Modified, aft 



rocess results in the 

 'er 

 The Human 



from the stomach to the ileo-cecal valve. 



In addition to this characteristic phy- 

 siologic movement it has also been ob- each segment of the contents into two, the 

 served by different experimenters that 

 the intestine manifests under special 

 circumstances two other forms of mov- 



ing waves, waves moving downward 23U2-? M f ^ 

 as well as upward from their point of 



origin, but without being preceded by an inhibition or relaxation. These 

 waves are therefore not regarded as true peristaltic waves. To avoid con- 

 fusion, the term diastalsis has recently been employed (Cannon) to desig- 

 nate the true peristaltic movement, viz.: progressive contraction preceded 

 by inhibition, and the terms katastalsis and anastalsis to designate the de- 

 scending and ascending contractions respectively, that occur without a fore- 

 running inhibition. 



Rush Peristalsis. Under conditions that are perhaps not strictly 

 physiologic, a rapid and far-reaching peristalsis is developed which may 

 pass over the intestine, from the duodenum to the cecum without stopping 

 in the course of 15 seconds, in the rabbit, and which has been designated 

 rush peristalsis. It is characterized by a wave of constriction preceded by 

 a completely inhibited long section of intestine. The contents of the in- 

 testine are carried along with extreme rapidity and vigor. The contrac- 



