330 MECHANISMS OF THE DIGESTIVE TRACT. 



marked than before, running as waves up or down the gut with a 

 rapidity of 2-4 cms. per second, they are totally unaffected by the 

 application of a strong stimulus to the intestine, either above or below 

 the segment which is under observation. Since the double effect of 

 local stimulation, augmentation above and inhibition below, is wanting, 

 the power of the intestine to move its contents in any definite direction 

 is also gone. A bolus placed in any part of the paralysed loop remains 

 absolutely motionless. 



Nothnagel l pointed out that the application of a crystal of sodium chloride 

 to the outer surface of the intestine causes in the rabbit and cat a ring of 

 constriction, not at the stimulated point, but immediately above it. He 

 rightly refers this effect to the stimulation of Auerbach's plexus, and contrasts it 

 with that produced by potassium salts, which excite the muscle fibres directly, 

 and therefore cause a ring of constriction at the stimulated spot. This 

 observer also noticed the inhibition in front of an advancing wave of con- 

 striction, which we have shown to be of so great importance for the normal 

 progress of the intestinal contents. 



The fact that the true peristalsis, dependent on the activity of the 

 local nerve centres, is only propagated in one direction, is well illustrated 

 by an experiment carried out by Mall. If a segment of intestine be 

 separated from the rest, and then resected in its former position, the 

 functions of the bowel are carried out in a perfectly normal fashion. 

 If, however, the resected loop be turned round, and connected with the 

 cut ends of the remaining intestine, so that its previously lower end is 

 connected with the upper part of the intestine, and its upper end is 

 directed towards the rectum, the animal dies after a time of intestinal 

 obstruction, due to the accumulation of indigestible material in the 

 gut above the resected loop. These experiments show that the propul- 

 sive movements of any part of the intestine always occur in one 

 direction. 



We have, therefore, in the normal animal to take into account only two 

 kinds of movement. The effect of the pendulum movement is to 

 thoroughly mix the contents of the intestine and bring them in intimate 

 contact with the mucous membrane of the wall. If an animal be fed 

 with pills containing bismuth subnitrate, and observed under the 

 Eontgen rays, it will be seen that the opaque pills move continually to 

 and fro in the lumen of the intestine, their actual progress towards the 

 colon being very small in comparison with the distance traversed 

 (Griitzner). 2 If the contents of the bowel are fluid, the mixing effects 

 due to the pendulum movements may predominate to such an extent 

 over the progression due to peristalsis, that foreign substances intro- 

 duced with large enemata into the rectum may travel up past the 

 ileo-csecal valve into the small intestine, or in rare cases may even 

 enter the stomach. Such a phenomenon has often been regarded as a 

 proof of the existence of anti-peristalsis in the normal gut, but is 

 probably sufficiently accounted for by the factors I have already 

 mentioned. 



Conditions of intestinal activity Circulation. The activity of 

 the intestines may be modified or called into play by a number of local 

 conditions. Chief among these are to be reckoned changes in the 

 circulation. According to some observers, local anaemia, induced by 



1 "Physiologie u. Pathologie des Darmes," Berlin, 1884. 



2 Arch.f. d. ges. PhysioL, Bonn, 1898, Bd. Ixxi. S. 492. 



