OSMOSIS AND DIGESTION 37 



4. What do you conclude, therefore, as to the effect of dias- 



tase on starch? 



5. Why is this change necessary if starch is to be used by 



plants ? 



50. To prove that starch is made soluble in growing plants. 



Laboratory Study No. 27. 



1. Pound two or three corn grains into a powder and put 



some of this corn meal into a test tube, add water, and 

 boil. To one-half of the mixture add iodine, and to the 

 other half, Fehling's solution, and boil. Give a careful 

 description of the experiment and state your observa- 

 tions and conclusions. 



2. Secure some germinating corn grains, cut them into small 



pieces, and test some of them with Fehling's solution as 

 in 1 above. Describe the experiment, stating your ob- 

 servations and conclusions. 



3. The change in starch that you have described is known 



as digestion. What reason have you for believing that 

 digestion of starch takes place when corn grains ger- 

 minate ? 



51. Definition of digestion. We may define digestion as 

 the chemical change whereby insoluble food substances are made 

 ready to pass through membranes and become ready for the use 

 of protoplasm. Let us now by experiment determine whether 

 or not protein needs digestion. 



52. Will protein pass through a membrane? Laboratory 

 Study No. 28. 



Thistle tube No. 4- Secure some white of egg, cut it with scis- 

 sors and mix it with water. (White of egg, we found, contains a 

 large amount of protein.) Prepare the fourth thistle tube in the 

 same way as directed for thistle tube No. 1 , only using white of egg 

 and water instead of grape sugar. See that the level of the liquid 

 is the same as in thistle tube No. 2. 



