THE MOVEMENTS OF THE STOMACH 701 



sphincter. The exact parts, however, played in this mechanism by the local 

 system and by the central nervous system respectively have not yet been 

 thoroughly made out, though there is no doubt that these movements may 

 proceed independently of any connection with the central nervous system. 



Stimulation of the peripheral end of the vagus nerves may exercise vary- 

 ing effects on the stomach wall as well as on its sphincters. In the normal 

 animal stimulation of the peripheral end of the vagus as a rule causes strong 

 contractions of the oesophagus as well as of the cardiac sphincter. After 

 the administration of atropine, stimulation of the same nerve will occasion 

 dilatation of the cardiac sphincter. On both cardiac and pyloric portions of 

 the stomach the vagus exercises inhibitory as well as augmentor effects. So 

 far as concerns the musculature of the fundus or body of the stomach, the 

 most usual effect is an inhibition during stimulation of the vagus succeeded 

 by an augmented tonus immediately the stimulus is removed. If the vagus 

 be excited a number of times the tonus of the muscular wall augments with 

 each stimulus. On the pyloric portion stimulation of the vagus also causes 

 inhibition, followed by contraction. The inhibition may, however, be very 

 short and in rare cases altogether absent, so that during the excitation this 

 inhibition is followed by a series of large rhythmic contractions. The pre- 

 vailing motor effect of the vagus therefore is in the fundus increased tonus, 

 in the pyloric portion augmented peristaltic waves. On the pylorus itself we 

 may obtain from vagal stimulation either increased or diminished contrac- 

 tion. The conditions under which each of these may be evoked have not yet 

 been definitely ascertained. Whether the splanchnic nerve, i.e. the sym- 

 pathetic system, has a direct influence on the movements of the stomach has 

 been disputed. According to Page May any effect produced by stimulation 

 of this nerve, generally consisting in diminished motor activity, is probably 

 due to the simultaneous influence on the vascular supply to the organ ; the 

 blood-vessels being constricted, an artificial anaemia is produced which in 

 itself is sufficient to account for diminished activity. Other observers regard 

 the splanchnic as having an influence on the stomach similar to its action on 

 the intestine, and regard it as the chief inhibitory nerve to this organ. It is 

 possible that the extent to which the stomach is brought under the control of 

 the sympathetic system may vary in different species of animals. 



Carlson has shown that the ' pangs of hunger ' are associated with and probably 

 due to rhythmic contractions of the stomach wall, which come on about meal time 

 especially if this be delayed. 



