724 PHYSIOLOGY OF DIGESTION AND SECRETION. 



and is passed only slowly into the colon through the ileocecal 

 sphincter. 



Rh'/thmical Movements. — In addition to the perist-altic wave a 

 second kind of movement may be observed in the small intestines. 

 It consists essentially in a series of local constrictions of the intes- 

 tinal wall, the constrictions occurring rhythmically at those points 

 at which masses of food lie. 



Cannon * has studied these movements most successfully by 



rn O O CD CD o L. 



Fig. 286. — Diagram to show the effect of the rhythmical constricting movements of 

 the small intestine upon the contained food. A string of food (1) is divided suddenly into 

 a series of segments (2) ; each of the latter is again divided and the process is repeated a 

 number of times (3 and 4). Eventually a peristaltic wave sweeps these segments forward 

 a certain distance and gathers them again into a long string, as in (1). The process of 

 segmentation is then repeated as described above. (Cannon.) 



means of the Roentgen rays. He finds that as a result of these 

 contractions the masses or strings of food lying in the intestine are 

 suddenly segmented, repeatedly and in a definite manner, into a 

 number of small pieces, which move to and fro as the pieces combine 

 and are again separated (see Fig. 286). These segmentations may 

 proceed at the rate of thirty per minute for a certain time, and the 

 apparent result is that the material is well mixed with the digestive 

 secretions and is brought thoroughly into contact with the absorp- 

 tive walls. During these rhythmical contractions there is no steady 

 progression of the food; it remains in the same region, although 

 subjected to repeated divisions. From time to time the separated 

 pieces are caught by an advancing peristaltic wave, moved 

 forward a certain distance, and gathered again into a new mass. 

 In this new location the rhythmical contractions again segment 

 and churn the mass before a new peristaltic wave moves it on. 

 According to this description, the rhythmical movements are 

 local contractions (mainly of the circular muscles) which seem 

 to be due to the local distention caused by the food. They occur 

 rhythmically for a certain period and then cease until a new series 

 is started, and it is obvious that they must play a very important 

 part in promoting both the digestion and absorption of the food. 

 Mallf has suggested that these rhythmical contractions of the 

 circular coats may also act as a pumping mechanism upon the 



* Cannon, "American Journal of Physiology," 6, 251, 1902. 

 t Mall, "Johns Hopkins Hospital Reports," 1896, i, 37. 



