MOVEMENTS OF THE STOMACH. 323 



The pylorus does not open at the approach of every wave, but only at irregular 

 intervals. The arrival of a hard morsel inhibits the opening of the sphincter, 

 and thus interferes with the passage of the already digested food. Thus the 

 motor functions of the stomach, which result in the mixing, trituration, and 

 expulsion of the food, are carried out almost entirely by the pyloric half of the 

 stomach. 



von Mering 1 has shown that when fluids alone are taken by the 

 mouth, their first discharge into the duodenum may occur within 

 ten minutes after the time at which they reach the stomach, and the 

 stomach may completely empty itself within twenty to twenty-five 

 minutes after the taking of fluid. This observer also pointed out that a 

 state of repletion of the small intestines reflexly slows the evacuation of 

 the stomach. The same effect may be produced by psychical excite- 

 ment. 



With regard to the causation of the gastric movements we know 

 very little. The stomach can be separated from all its nervous con- 

 nections, and indeed cut out of the body, without abolishing the con- 

 tractions. These, therefore, must have their origin in the walls of the 

 stomach itself. A number of small ganglia are to be found in the walls 

 of this organ, and have been regarded as local centres for the production 

 and co-ordination of the contractions. 2 It is more probable, however, 

 that here, as in the heart, the contraction wave is originated and pro- 

 pagated in the muscular tissue itself. That the stimulus to contraction 

 is not in the main afforded by the distension of the stomach, is shown 

 by the fact that the movements become more vigorous as digestion 

 proceeds, and as the stomach empties more of its contents into the 

 duodenum. It has been thought, therefore, that the chief exciting 

 cause of the movements is the acidity of the gastric contents, which 

 increases steadily with the progress of digestion. 



Although contractions of the stomach can be produced locally, this 

 local reaction is aided by reflex impulses carried out through the inter- 

 mediation of the central nervous system. The stomach is supplied with 

 nerves from two sources, namely, from the vagi, and from the dorsal 

 region of the spinal cord through the sympathetic chain and splanchnics. 

 The exact nature of the impulses carried by these nerves cannot yet be 

 regarded as finally settled. All observers, however, agree in describing 

 the vagus as a motor nerve for the stomach. According to S. Mayer, 3 

 the results of exciting the peripheral end of the vagus in the neck may 

 be one of three (1) A contraction of the cardiac end, which gradually 

 advances towards the pylorus ; (2) the groove present in the region of 

 the transverse band deepens, and similar constrictions appear in other 

 parts of the stomach ; (3) the whole muscular wall enters into a state of 

 tonic contraction, which comes on slowly and lasts a considerable time. 



More or less similar results have been obtained by Longet, 4 Goltz, 5 

 v. Braam Houckgeest, 6 Openchowski, 7 Morat, 8 and others. According to 

 v. Braam Houckgeest and Morat, the motor effects are obtained more 



1 Verhandl. d. xii Cong. f. innere Med., Wiesbaden, 1893. 



2 Cf. Openchowski, Arch. f. PhysioL, Leipzig, 1889, S. 549. 



3 Hermann's "Handbuch," Bd. v. (2), S. 431. 



4 " Traite* de physiologic," 3rd ed., tome i. p. 148 (quoted by S. Mayer). 



5 Arch./, d. ges. PhysioL, Bonn, 1872, Bd. vi. S. 616. 



6 Ibid., 1872, Bd. vi. S. 266. 



7 Arch./. PhysioL, Leipzig, 1889, S. 549. 



8 Arch, de physiol, norm, etpath., Paris, (5), tome v. p. 142. 



