PROBLEM 50 69 



4. Why is it necessary that plants digest starchy and other 

 foods? 



Problem 48 : What changes take place in starchy foods in 

 the mouth? (Demonstration.) 



Materials. — Cracker, Fehling's solution, Bunsen burner, test 

 tube. 



Method and Observations. — Chew an unsweetened cracker 

 slowly. Note any change in taste. Test some of the unchewed 

 cracker with Fehling's solution. Result? Place a little of the 

 chewed cracker and saliva in a test tube, add Fehling's solution, 

 and heat. What happens ? 



Conclusion. — What happens to starchy foods in the mouth? 

 Of what use might this be to man ? 



Problem 49 : Conditions necessarj/ for the action of diastase. 



Materials. — Test tubes, diastase, starch paste, ice, Fehling's 

 solution, Bunsen flame, test-tube rack. 



Method. — Place a Httle diastase in three test tubes containing 

 starch paste. Label them 1, 2, and 3. Place 1 in the icebox on 

 the ice ; boU the contents of 2 and then place it with 3 in the test- 

 tube rack in the laboratory. 



Observations. — After 24 hours test the contents of each of the 

 three tubes for sugar. Has digestion taken place in all tubes? 



Note. — Diastase has thus been shown to act only under certain conditions. 

 Water must be present and a certain temperature. Its action may be prevented 

 by extreme heat. In these respects it acts as if it were like a living substance. 



Conclusion. — What conditiocs are most favorable to digestion 

 by the diastase? 



Note. — Pure diastase must be used for this experiment. Most diastase prepa- 

 rations contain grape sugar. 



Problem, 50 : What is the reason for digestion of starch in 

 the com grain ? 



Materials. — Funnels, filter paper, starch, sugar, beaker. 



Method. — • Take two funnels, place filter papers within each. 

 In one funnel place a mixture of starch and water, in a second a 



