184 APPENDIX 



Students get materials from center table to fill test-tubes. Be 

 sure that everything is clearly labeled. Insist that students 

 use care and get the right materials. 

 Amounts of materials for students to take: 



Distilled water, 1/2 test-tube full, or less. 



Fibrin, one small piece. 



Pepsin, 1/^ pipette full (explain how pepsin is prepared). 



Hydrochloric acid, 2 drops. 



Have students wash test-tubes at end of experiment. 



B. Salivary digestion (Exercise 9, Frog) 



Equipment for students: (students work singly). 

 3 test-tubes for each student. 

 3 gummed labels for each student. 



General equipment: 

 Gas burners. 

 Test-tube racks. 

 Test-tube brushes. 

 Matches. 

 Pipettes. 



Starch paste (formula on page 183). 

 Iodine (page 182). 



Benedict's or Fehling's solution (pages 181-182). 

 Directions for students: 



To test for starch: Put a drop of the solution to be tested on 



a clean glass slide and add a drop of iodine. A dark blue 



color means starch is present. 

 To test for sugar: Heat 10 c.c. of the solution to be tested in 



a test-tube with half as much of Benedict's (or Fehling's) 



solution. A greenish-yellow precipitate (or brick-red) 



means a reducing sugar is present. 

 Rinse test-tubes with distilled water. 

 Label each tube, telling what it is to receive. 

 Amounts of materials: 



Starch solution, 10 c.c, or to a depth of about one inch in 

 bottom of tube. 



Saliva, 5 c.c, or to a depth of about half an inch in bottom 

 of tube. 

 Test each tube first for starch and second for sugar. 

 Keep all tests till the experiment is finished. 

 Have students wash tubes at close of experiment. 



