726 PHYSIOLOGY OF DIGESTION AND SECRETION. 



relax. The wave of constriction may be recorded by the use of 

 suitable apparatus. When thus recorded it is found that the ad- 

 vancing area of constriction is preceded by an area of inhibition 

 or relaxation, so that the peristaltic movement consists of two parts, 

 following in a definite sequence, which seem to combine to facili- 

 tate the movement onward of the intestinal contents; for it is 

 obvious that the wave of constriction will be more effective in 

 forcing the contents forward if just in front of it the intestine is 



Fig. 285. Peristaltic contraction of the small intestine (dog). The horizontal line gives 

 the time in seconds. The curve was obtained by recording the diameter of the intestine at 

 a given point during the passage of a peristaltic wave. It will be seen that there was first a 

 dilatation (wave of inhibition), followed by a strong contraction. The smaller waves on the 

 intestinal curve are due to the effect of the respiratory movements on the recording mechanism. 



relaxed by inhibition of the tonicity of the muscular coat (Fig. 285). 

 Bayliss and Starling,* to whom we owe the discovery of this two- 

 fold character of the movement, regard it as a reflex which is con- 

 trolled within the intestinal wall itself through its intrinsic ganglia 

 and their afferent and efferent connections. When a bolus is 

 inserted into the intestine at any point its effect upon the sensory 

 fibers is such as to cause a reflex contraction of the muscle above the 

 bolus, that is, toward the stomach, and a reflex inhibition or 

 dilatation below. They speak of this definite relationship as the 

 law of the intestine; it is described also under the name my en- 

 teric reflex. It is obvious that the circular layer of muscles is 

 chiefly involved in peristalsis, since constriction can only be pro- 

 duced by contraction of this layer. To what extent the longitudi- 

 nal muscles enter into the movement is not definitely determined. 

 The term "antiperistalsis" is used to describe the same form of 

 movement running in the opposite direction that is, toward the 

 stomach. Antiperistalsis is said not to occur under normal condi- 

 tions ; it has been observed in isolated pieces of intestine or in the ex- 

 posed intestine of living animals when stimulated artificially or after 

 * Bayliss and Starling, "Journal of Physiology," 24, 99, 1899. 



