ALIMENTATION AND DIGESTION 113 



of the pyloric portion and pass onward to the pylorus itself, 

 a new ring beginning about once every ten seconds and con- 

 suming from thirty to forty seconds in passing to the pylorus. 

 Consequently there are always two or more slowly moving 

 rings in the pyloric end of the stomach at one time. 1 



The pyloric end of the stomach is thus the seat of a combined 

 chemical and mechanical action on the food. The vegetable 

 foods are softened, while the connective tissue of the animal 

 foods is dissolved away ; in addition, the food is mixed with 

 a considerable amount of liquid supplied by the secretion of 

 gastric juice. The contents of the pyloric end of the stomach 

 thus ultimately come to consist of minute solid masses sus- 

 pended in a liquid, the consistency of the whole being that 

 of moderately thick pea soup. This product of the work of 

 the stomach is known as chyme. 



23. The expulsion of chyme into the intestine. The open- 

 ings of the oesophagus and intestine into the stomach are 

 usually closed ; the former is opened normally only during 

 the act of swallowing, while the latter opens at irregular 

 intervals during the process of gastric digestion. The open- 

 ing of the pylorus allows the rings of constriction moving 

 over that region of the stomach to discharge the semifluid 

 chyme into the intestine. If, however, a large mass of solid 

 food arrives and is driven against the walls, the pylorus 

 reflexly closes, thus guarding the entrance of the intestine 

 from the passage of food not yet ready for intestinal diges- 

 tion. The pressure exerted by the sustained contraction of 

 the walls of the cardiac end of the stomach adds to the 

 food in the pyloric region new portions from time to time, 

 and the same combined chemical and mechanical process 

 already described is continued until the whole mass is 

 reduced to chyme and driven into the intestine. 



1 These movements of the stomach and intestine are well shown in 

 zoetrope figures, which may be obtained from the Harvard Apparatus 

 Company, Back Bay Post Office, Boston. 



