730 PHYSIOLOGY OF DIGESTION AND SECRETION. 



The Relation of the Nerves to the Movements of the 

 Stomach. The stomach receives nerve fibers from two sources, 

 the vagi and the splanchnics, but its orderly movements are merely 

 regulated through these extrinsic fibers; it is essentially an auto- 

 matic organ. Thus, it has been shown that the excised stomach 

 (Hofmeister and Schutz), when kept warm, continues to execute 

 regular movements which, if not identical with those observed under 

 normal conditions, have at least an orderly sequence. So also it 

 would appear from the results of several observers * that gastric 

 digestion may proceed normally both as regards secretion and 

 movements after section of the extrinsic nerves. We may regard 

 the stomach, considered as a motor mechanism, as an automatic 

 organ like the heart. Its stimuli to movement arise within itself, 

 but these movements are regulated by the action of the extrinsic 

 nerve fibers so as to adapt them to varying conditions. Whether 

 the automaticity is a property of the plain muscle tissue itself, or 

 depends upon the rich supply of intrinsic nerve ganglia (plexuses of 

 Meissner and Auerbach), is a question that cannot be answered 

 definitely at present. The extrinsic nerves not only supply the 

 stomach with efferent fibers, motor and secretory, but also carry 

 afferent fibers from the stomach to the central nervous system. 

 Regarding the purely efferent 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 causing more or less well-marked con- 

 tractions 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 muscu- 

 lature is supplied by motor fibers from these nerves. The fibers 

 coming through the splanchnics, on the contrary, are mainly inhib^ 

 itory. 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 physiological varieties. Through their activity, 

 without doubt, the movements of the stomach may be influenced, 

 favorably or unfavorably, by conditions directly or indirectly affect- 

 ing the central nervous system. Wertheimer f has shown experi- 

 mentally that stimulation of the central end of the sciatic or the 

 vagus nerve may cause reflex inhibition of the tonus of the stomach, 



* See Heidenhain in Hermann's "Handbuch der Physiologic," vol. v., 

 p. 118. Also Cannon, "American Journal of Physiology," 1906. 



f "Archiv de physiologic normale et pathologique," 1892, p. 379. 



