310 ESSENTIALS OF PHYSIOLOGY. 



fundus (namely, the dome-shaped part of the organ above the entrance 

 of the oesophagus) become tonically contracted. Waves of contrac- 

 tion occur in the pyloric portion, beginning about the middle of the 

 stomach and travelling at the rate of about three a minute towards the 

 pylorus. The stomach contents are propelled by these waves towards 

 the pylorus, and if the opening is kept closed by the contraction of the 



FIG. 121. Tracing showing initial relaxation followed by contraction of the muscular 

 wall of the stomach on stimulation of vagus nerves. (Elliott.) 



sphincter, they return by an axial stream towards the body of the 

 stomach. In this way complete mixture with the gastric juice is 

 effected. As digestion proceeds and the food is brought into a more 

 fluid state, the sphincter undergoes periodic relaxation, opening every 

 few minutes to allow the passage of the semi-liquid material into the 

 duodenum. By the tonic contraction of the fundus and body, the food 

 is little by little subjected to the action of the pyloric mill, and subse- 

 quently passed on to the duodenum ; and as the contents of the 

 stomach are thus gradually diminished in quantity, the organ becomes 



