DIGESTION AND ABSORPTION. 159 



tract, place the mixture in the incubator; shake fre- 

 quently; after fifteen minutes test for reducing sugar. 

 There will probably be a relatively small amount of 

 reducing sugar. If one watches the progress of the 

 digestion for several hours he will be convinced that 

 the cooking of starch very greatly facilitates its diges- 

 tion by saliva. 



(10) Boil a few cubic centimeters of saliva; add starch 

 paste; place in the incubator for ten minutes; test for 

 reducing sugar. What is the verdict? 



(11) Test the salivary secretion with neutral litmus. 

 Determine whether its faint, alkaline reaction is essen- 

 tial to its action as a digestive fluid. 



() To one portion of saliva add an equal volume 

 of 0.3% hydrochloric acid and the same amount 

 of starch paste. The mixture represents 0.1% 

 hydrochloric acid. Place the mixture in the 

 incubator for fifteen minutes; test with Fehling's 

 solution. Verdict ? 



() Repeat the experiment substituting, for the 

 hydrochloric acid, lactic acid of the same strength; 

 place in the incubator for fifteen minutes; test with 

 Fehling's solution. 



What is the conclusion ? 



(12) To determine the course of salivary digestion. Mix 

 50 c. c. of salivary extract with an equal amount of 

 starch paste. Test a portion with iodine at once. 

 Test another portion at once with Fehling's solution. 

 Keep the beaker in a water bath at blood tempera- 

 ture. Test a portion of the mixture every minute 

 with iodine and another portion every minute with 

 Fehling's solution. 



(a) What is the first change noted in the digestion 

 of the starch ? 



