GASTRIC JUICE AND GASTRIC DIGESTION 381 



8. The Action of Ptyalin is Favored by the Removal of the End 

 Products. Place 50 c.c. of 2 per cent, starch paste in a dialyzing tube or 

 paper, suspend in a beaker of running water. Take 50 c.c. of the same 

 solution in a beaker, to each add 2 c.c. of saliva and mix thoroughly. Test 

 for the disappearance of starch at intervals of 20 minutes. The starch in 

 the dialyzing tube will disappear first because the reducing sugar passes out 

 through the dialyzer, while in the beaker it is retained and hinders the further 

 action of ptyalin. 



II. GASTRIC JUICE AND GASTRIC DIGESTION. 



9. The Secretion of Gastric Juice. The conditions which influence 

 gastric secretion can be readily observed on the dog with a gastric fistula. 

 Take a dog which has had a gastric fistula (prepared some weeks before) and 

 which is in a condition of hunger, place him in a holder with a cup suspended 



FIG. 278. Operation on the Stomach to Form an Isolated Pouch with Nerves Intact. 

 S, Isolated sac; V, cavity of stomach; A, A, opening at the abdominal wall. 



to collect the gastric juice, and exhibit before the dog some fresh meat or 

 other food which he enjoys, but do not allow him to eat it. After teasing the 

 animal for 5 or 10 minutes, an abundant flow of gastric juice will begin. 

 Pawlow calls this the psychic secretion. 



If an esophageal fistula has also been performed the dog may be allowed 

 to eat the meat, of course swallowing it out of the esophageal fistula back into 

 the plate. In this experiment an abundant flow of gastric secretion takes 

 place and may continue for an hour or more. 



If a gastric pouch has been performed by Pawlow's method, the animal 

 mav be allowed to eat the food, swallowing it into the stomach. In this case 



