OSMOSIS AND DIGESTION 33 



tube, membrane down, in one of the wide-mouthed bottles and fill 

 it with water up to the neck. Add grape sugar solution to the thistle 

 tube until the level of the water in the bottle and that of the 

 liquid in the thistle tube is the same. Connect a long piece of 

 glass tubing to the upper end of the inverted thistle tube, and 

 support this tube in a vertical position, so that the membrane does 

 not touch the bottom of the bottle (Fig. 8). 



Thistle tube No. 2. Set up a control experiment exactly like 

 No. 1, except that water should be put into the thistle tube as well 

 as in the bottle. 



44. Will water pass through a membrane ? Laboratory 

 Study No. 22. 



1. Give in your own words a description of the way thistle 



tube No. 1 was prepared, making a diagram of the 

 apparatus, and labeling level of water in bottle 

 and of grape sugar solution in thistle tube at the 

 beginning of the experiment. 



2. At the end of a few hours compare the level of the liquid 



in thistle tube No. 1 with the level in thistle tube 

 No. 2. 



a. How many inches has the grape sugar risen in No. 1 ? 



b. Is there a similar rise in the water in thistle tube 



No. 2? 



c. What must have passed into thistle tube No. 1 to 



cause the liquid to rise? 



d. Through what must this liquid have passed to get 



into the thistle tube? 



3. Do you conclude, therefore, that water will or will not 



pass through a membrane ? 



45. Will grape sugar pass through a membrane? Labor- 

 atory Study No. 23. 



1. At the end of a few hours test the liquid in bottle No. 1 

 by putting a glass tube to the bottom of the bottle, 

 pressing the thumb over the top of the tube, and 

 removing the sample of liquid thus obtained to a 

 clean test tube; add Fehling's solution and boil. 



