MOVEMENTS OF THE ALIMENTARY CANAL. 667 



The peristaltic movements of the intestines may be observed 

 upon living animals when the abdomen is opened. If the operation 

 is made in the air and the intestines are exposed to its influence, or 

 if the conditions of temperature and circulation are otherwise 

 disturbed, the movements observed are often violent and irregular. 

 The peristalsis runs rapidly along the intestines and may pass over 

 the whole length in about a minute; at the same time the con- 

 traction of the longitudinal muscles gives the bowels a peculiar 

 writhing movement. Movements of this kind are evidently 

 abnormal, and only occur in the body under the strong stimulation 

 of pathological conditions. Normal peristalsis, the object of which 

 is to move the food slowly along the alimentary tract, is quite a 

 different- affair. Observers all agree that the wave of contraction 

 is gentle and progresses slowly, although at different rates perhaps 

 in different parts of the intestine. According to Bayliss and Star- 

 ling,* the peristaltic movement is a complicated reflex through the 

 intrinsic ganglia. When the intestine is stimulated by a bolus 

 placed within its cavity, the musculature above the point stimulated 

 is excited, while that below is inhibited. In accordance with this 

 law they find that in peristalsis the advancing wave of constriction 

 is preceded by a wave of relaxation or inhibition. The force of the 

 contraction as measured by Cash f in the dog's intestine is very small. 

 A weight of five to eight grams was sufficient to check the onward 

 movement of the substance in the intestine and to set up violent, 

 colicky contractions which caused the animal evident uneasiness. 



Mechanism of the Peristaltic Movement. The means by which 

 the peristaltic movement makes its orderly forward progression 

 have not been determined beyond question. The simplest explana- 

 tion would be to assume that an impulse is conveyed directly from 

 cell to cell in the circular muscular coat, so that a contraction started 

 at any point would spread by direct conduction of the contraction 

 change. This theory, however, does not explain satisfactorily the 

 normal conduction of the wave of contraction always in one direc- 

 tion, nor the fact that the wave of contraction is preceded by a 

 wave of inhibition. Moreover, Bayliss and Starling state that, 

 although the peristaltic movements continue after section of the 

 extrinsic nerves, indeed, become more marked under these con- 

 ditions, the application of cocain or nicotin prevents their oc- 

 currence. Since these substances may be supposed to act on the 

 intrinsic nerves, it is probable that the co-ordination of the move- 

 ment is effected through the local nerve ganglia, but our knowledge 

 of the mechanism and physiology of these peripheral nerve-plexuses 

 is as yet quite incomplete. 



*" Journal of Physiology," 24, 99, 1899. 



t " Proceedings of the Royal Society," London, 41, 1887. 



