722 PHYSIOLOGY OF DIGESTION AND SECRETION, 



empties itself after a meal the peristaltic waves of contraction arise 

 nearer and nearer to the cardiac end and pass over gradually into 

 the hunger contractions characteristic of the empty stomach. 



Movements of the Intestines. — ^The muscles of the small and 

 the large intestine are arranged in two layers, — an outer longitudinal 

 and an inner circular coat, — while between these coats and in the 

 submucous coat there are present the nerve-plexuses of Auerbach 

 and Meissner. The general arrangement of muscles and nerves is 

 similar, therefore, to that prevailing in the stomach, and in accor- 

 dance with this we find that the physiological activities exhibited 

 are of much the same character, only, perhaps, not quite so complex. 



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. 



Two main forms of intestinal movement have been distin- 

 guished — the peristaltic and the pendular or rhythmic. 



Peristalsis. — The peristaltic movement consists in a constric- 

 tion of the walls of the intestine, which, beginning at a certain 

 point, passes downward away from the stomach. The wave of 

 constriction may be recorded by the use of suitable apparatus. 

 When thus recorded it is found that the advancing area of con- 

 striction 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 facilitate 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 relaxed by 

 inhibition of the tonicity of the muscular coat (Fig. 285). Bayliss 

 and Starhng,* to whom we owe the discovery of this twofold 

 character of the movement, regard it as a reflex which is controlled 

 within the intestinal wall itself through its intrinsic gangUa and 

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



