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EXPERIMENTAL PHYSIOLOGY 



of two pyrex glass tubes filled with water containing a few drops 

 of phenolsulphonephthalein. Determine the pH of the water by 

 comparing with known standards. Tap water is slightly alkaline. 

 The tubes should be tightly ctfrked with exclusion of air. Place one 

 tube in the dark, the other in direct sunlight. Note the change in 

 hydrogen-ion concentration in the two tubes after 2-3 hours or 

 less if the sunlight proves injurious to the planaria. If the planaria 

 give out CO2 the solution should become more acid, if they use 

 up CO2 the solution should become more alkaline. 



(2) Repeat the experiment using a water plant, e.g., spirogyra, 

 instead of the planaria, and having the water distinctly acid to 

 start with by bubbling through it CO 2 from your breath. 



In the tube placed in sunlight bubbles may appear and a gas 

 collect. Determine the nature of this gas by an appropriate test. 



