6*2 CELL-CONTENTS AND CELL-WALLS. 



(c) Make experiments with a dialyser ( 44) to ascer- 

 tain whether or not (a) starch mucilage and (6) sugar 

 solution can pass through a membrane. From time to 

 time take out some of the water and test it with iodine 

 in the case of the starch ; with Fehling's solution in the 

 case of sugar. 



(d) Repeat the dialysis experiment with starch solution 

 to which some saliva or diastase has been added ; after an 

 hour test the water with Fehling (sugar present). As a 

 control, set up a second dialyser containing saliva which 

 has been boiled before being added to the starch. 



(e) Label three test-tubes A, B, C. In A put some 

 starch solution ; in B saliva only ; in C one part of saliva 

 and three parts of starch solution. Place the three tubes 

 in a beaker of water at 40 C. for about ten minutes ; to 

 maintain the temperature, set the beaker on a sand-bath 

 with a thermometer suspended in the water. Then test 

 portions of the three liquids for reducing sugar with 

 Fehling's solution ; C reduces Fehling, A and B do not. 

 Also test a portion of each with a few drops of iodine ; 

 only A gives a blue colour; the starch in C has been 

 changed into maltose. 



(/) Label two test-tubes A and B, and place in each 

 some thick opalescent starch paste ; to B add some saliva, 

 and keep both A and B at 40 C. A remains unchanged, 

 but in a minute or so B begins to become liquid and clear 

 a process preparatory to the conversion of the starch 

 into sugar. 



(g) Label three test-tubes A, B, G. Into A put some 

 saliva and boil it, then add thin starch paste ; into B put 

 starch paste, saliva, and a little hydrochloric acid ; into C 

 starch paste, saliva, and a little potash. Keep all three 

 at 40 C., and after ten minutes test each with Fehling ; 

 no sugar is present in either diastase is destroyed by 

 boiling, and its action is arrested by acids and alkalis. If 

 B and C are very carefully neutralised (B with potash, 

 C with acid) , the diastase may be enabled to act as usual. 



(h) Into a test-tube place some thick starch paste, add 

 galiva, and place the tube in a freezing mixture. After 



