256 HANDBOOK OF PHYSIOLOGY. 



distance of three or four inches. The object of this movement appears 

 to be, as just said, to carry the food towards the pylorus as fast as it is 

 formed into chyme, and to propel the chyme into the duodenum ; the 

 undigested portions of food being kept back until they are also reduced 

 into chyme, until all that is digestible has passed out. The action of 

 these fibres is often seen in the contracted state of the pyloric portion of 

 the stomach after death, when it alone is contracted and firm, while the 

 cardiac portion forms a dilated sac. Sometimes, by a predominant ac- 

 tion of strong circular fibres placed between the cardia and pylorus, the 

 two portions, or ends as they are called, of the stomach, are partially 

 separated from each other by a kind of hour-glass contraction. By 

 means of the peristaltic action of the muscular coats of the stomach, not 

 merely is chymified food gradually propelled through the pylorus, but a 

 kind of double current is continually kept up among the contents of the 

 stomach, the circumferential parts of the mass being gradually moved 

 onward towards the pylorus by the contraction of the muscular fibres, 

 while the central portions are propelled in the opposite direction, name- 

 ly, towards the cardiac orifice ; in this way is kept up a constant circu- 

 lation of the contents of the viscus, highly conducive to their free 

 mixture with the gastric fluid and to their ready digestion. 



Influence of the Nervous System on Gastric Digestion. The 

 normal movements of the stomach during gastric digestion are directly 

 connected with the plexus of nerves and ganglia contained in its walls, 

 the presence of food acting as a stimulus which is conveyed to the gang- 

 lia and reflected to the muscular fibres. The stomach is, however, also 

 directly connected with the higher nerve-centres by means of branches 

 of the vagus and solar plexus of the sympathetic. The vaso-motor 

 fibres of the latter are derived, probably, from the splanchnic nerves. 



The exact function of the vagi in connection with the movements of 

 the stomach is not certainly known. Irritation of the vagi produces 

 contraction of the stomach, if digestion is proceeding; while, on the 

 other hand, peristaltic action is retarded or stopped, when these nerves 

 are divided. 



Bernard, watching the act of gastric digestion in dogs which had 

 fistulous openings into their stomachs, saw that on the instant of divid- 

 ing their vagi nerves, the process of digestion was stopped, and the 

 mucous membrane of the stomach, previously turgid with blood, became 

 pale, and ceased to secrete. These facts may be explained by the theory 

 that the vagi are the media by which, during digestion, an inhibitory 

 impulse is conducted to the vaso-motor centre in the medulla; such im- 

 pulse being reflected along the splanchnic nerves to the blood-vessels of 

 the stomach, and causing their dilatation (Rutherford). From other 

 experiments it may be gathered, that although division of both vagi 

 always temporarily suspends the secretion of gastric fluid, and so arrests 



