354 



FOOD AND DIGESTION 



tion and mix. At intervals of 2 to 5 minutes test these 3 samples for the dis- 

 appearance of starch and appearance of reducing sugar, as in experiment 5. 

 No change will take place in a; b will be quickly digested; and the digestion 

 in c will be slight or suspended. Upon placing c in a warm bath digestion will 

 quickly occur. 



7. Influence of Acids and Alkalies on Salivary Digestion. To 

 each of 5 test tubes, a, b, c, d, e, add 5 c.c. of saliva. Leave a for the normal; 

 make b strongly alkaline; c exactly neutral; d acid to the extent of 0.2 to 0.3 per 

 cent hydrochloric acid; e strongly acid. Place all in the water bath at 40 C. 

 Add to each 2 c.c. of i per cent starch paste and mix. Test for starch and for 

 reducing sugar at intervals of 20 minutes and compare, noting the results 

 in the following table: 



The results obtained in the 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 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 dis- 

 appearance 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. 



