644 PHYSIOLOGY OF DIGESTION AND SECRETION. 



action of the extrinsic nerves, the results of numerous experiments 

 seem to show quite conclusively that in general the fibers received 

 along the vagus path are motor, artificial stimulation of them caus- 

 ing more or less well marked contractions of part or all of the 

 musculature of the stomach. It has been shown that the sphincter 

 pylori as well as the rest of the musculature is supplied by motor 

 fibers from these nerves. The fibers coming through the splanch- 

 nics, on the contrary, are mainly inhibitory. When stimulated 

 they cause a dilatation of the contracted stomach and a relaxation 

 of the sphincter pylori. Some observers have reported experiments 

 which seem to show that this anatomical separation of the motor 

 and inhibitory fibers is not complete; that some inhibitory fibers 

 may be found in the vagi and some motor fibers in the splanchnics. 

 The anatomical courses of these fibers are insufficiently known, but 

 there seems to be no question as to the existence of the two physio- 

 logical varieties. Through their activity, without doubt, the move- 

 ments of the stomach may be influenced, favorably or unfavorably, 

 by conditions directly or indirectly affecting the central nervous 

 system. Wertheimer* has shown experimentally that stimulation 

 of the central end of the sciatic or the vagus nerve may cause reflex 

 inhibition of the tonus of the stomach, and Doyonf has confirmed 

 this result in cases in which the movements and tonicity of the stom- 

 ach were first increased by the action of pilocarpin and strychnin. 

 Cannon, in his observations upon cats, found that all movements 

 of the stomach ceased as soon as the animal showed signs of anxiety, 

 rage, or distress. 



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. 



Two main forms of intestinal movement have been distinguished, 

 the peristaltic and the pendular. 



Peristalsis. The peristaltic movement consists in a constriction 

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

 passes downward away from the stomach, from segment to segment, 

 while the parts behind the advancing zone of constriction gradually 

 relax. The evident effect of such a movement is to push onward the 

 contents of the intestines in the direction of the movement. It is 

 obvious that the circular layer of muscles is chiefly involved in 



* "Archives de physiologic normale et pathologique, " 1892, p. 379. 

 f Ibid., 1895, p. 374. 



