402 



FOOD AND DIGESTION 



The results obtained in Experiments 5, 6, and 7 show that starch is 

 converted into reducing sugar, and furthermore, that the conditions for its 

 conversion indicate that the change is accomplished by an amylolytic enzyme 

 which in this case is called ptyalin. 



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

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

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

 solution in a beaker, to each add 2 cc. 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 

 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 



