12 PHYSIOLOGY OF ALIMENTATION. 



running before it as indicated in Fig. 2 (11.30-1.30). Between 

 the rings of constriction the stomach is bulged out. CANNON 

 has calculated the number of waves which pass over the 

 stomach during a single digestive period lasting approxi- 

 mately seven hours as 2600. 



The food slowly passes out of the stomach into the duode- 

 num. The exact manner in which this happens has, however, 

 been variously described by different authors. Those who 

 with HIRSCH saw the food pass from the stomach into the 

 duodenum at intervals are probably correct. In cats, CANNON 

 found that no food appeared in the duodenum until the con- 

 strictions had been passing over the antrum for ten or fifteen 

 minutes. When the food did appear it was squirted through 

 the pylorus for some distance along the intestine. Every 

 constriction wave does not force food through the pylorus. 

 Several waves usually pass over the antrum before one is ef- 

 fective in this particular. At times two or three succeeding 

 waves may each force food through the pylorus, but usually 

 it remains closed for some time after it has allowed one con- 

 striction wave to pass food into the duodenum. The cause 

 of this opening and closing of the pylorus will be discussed 

 further on. 



When a hard bit of food reaches the pylorus the sphincter 

 closes tightly and remains closed longer than when the food 

 is soft. This can be shown experimentally by feeding along 

 with an ordinary meal pellets of bismuth subnitrate made up 

 with starch paste. These can be readily recognized as 

 darker spots in the general shadow cast by the gastric contents 

 upon the fluoroscopic screen. When such pellets are given 

 with the regular meal the stomach is emptied more slowly 

 than when the food has a uniform consistency. 



We have thus far spoken only of the movements of the 

 pyloric half of the stomach. How does the cardiac half 

 behave? For many years this has been looked upon as a 

 sort of reservoir for the swallowed food, but it has always 

 been considered purely passive, CANNON'S experiments 



