MOVEMENTS OF THE ALIMENTARY CANAL. 



in much the same way as happens in the case of the spleen. Bay i 3 

 and Starling corroborate this view, except that they find that b\t 

 the circular and longitudinal layers of muscle are concerned in 

 movement. The rhythmical contractions, according to theVe' 

 observers, are entirely muscular in origin, since they persist afteV 7^ 

 the application of nicotin or cocain. Vfi 



Cannon* has studied the movements of the small intestines most 

 successfully by means of the Roentgen rays. He finds, in the cat, 

 that the most characteristic phenomenon is that due to the rhyth- 

 mical or pendular movements. By means of these contractions 

 masses or strings of the food 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. 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 absorptive 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, as it were, 

 by an advancing peristaltic wave, moved forward a certain dis- 

 tance, 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 

 distension caused by the food. They occur rhythmically for a 

 certain period and then cease until a new series is started. Some- 

 what similar movements have been described by Bunch f from 

 observations on the isolated intestine. The curious observation is 

 reported J that during the period of fasting (dog) the whole gastro- 

 intestinal canal, although empty, shows at intervals rhythmical 

 contractions of its musculature which may last for twenty to thirty 

 minutes (see p. 703). 



The Nervous Control of the Intestinal Movements. As 

 stated, there is some evidence to show that the rhythmical con- 

 tractions of the intestines are muscular in origin (myogenic), while 

 the more co-ordinated peristaltic movements depend upon the 

 intrinsic nervous mechanism. The intestine is, however, not de- 

 pendent for either movement upon its connections with the central 

 nervous system. Like the stomach, it is an automatic organ whose 

 activity is regulated through its extrinsic nerves. 



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



t Bunch, " Journal of Physiology," 22, 357, 1897. 



I Boldireff, "Archives des sciences biologiques, " 11, 1, 1905. 



