8 



THE FROG 



period. Record your observations and make a general concluding 

 statement concerning the conditions under which digestion occurs in 

 the tubes. This is to be done in the form of a table such as the one 

 shown in Fig. 11. 



Gastric Digestion 



Fig. U. — Form of table for record of Exercise 8. 



Exercise 9. — Salivary Digestion. 



(h) In order to find out how salivary digestion occurs fill each of 

 two test-tubes to a depth of one inch with starch paste. Test the con- 

 tents of the first tube for starch as follows : Transfer with your pipette 

 two drops of the starch paste to a glass slide. Add to this one drop 

 of iodine solution. A blue color reaction with iodine indicates the 

 presence of starch. Now test the remaining contents of tube 1 for 

 sugar, as follows: Add to the contents of the tube half as much 

 Benedict's or Fehling's solution, mix, and heat. Keep the solution in 

 the tube agitated in order to avoid burning yourself. A yellow or red 

 precipitate indicates the presence of sugar. To the starch paste in the 

 second tube add half as much saliva from your mouth. Mix thor- 

 oughly and let stand for ten minutes. Test the contents of tube 2 

 for starch and sugar as described above. If digestion is not complete 

 a purplish color with iodine will indicate the presence of erythro- 

 dextrin. Collect some saliva in a third test-tube and test for starch 

 and sugar as described above. Keep all tests until the experiment is 

 completed. Record the results of the tests and make a general con- 

 cluding statement concerning the changes which occur in salivary 



