PRACTICAL PHYSIOLOGY 



Saturated solution of 

 zinc sulphate. 



moistened with starch so- 

 lution containing iodide 

 of potassium. Iodine is 

 set free at the anode and 

 turns the starch blue. 

 Feeble differences of elec- 

 trical potential are de- 

 termined and estimated 

 by other methods (gal- 

 vanometer, electrometer), 

 which will be studied 

 later. 



Keys. Any apparatus 

 which is used for inter- 

 rupting or diverting the 

 course of a current is 



called a key or switch. The keys used in physio- 

 logical experiments are arranged to close and open 



Clay plug, moistened 

 with salt solution. 



FlG. 7. NON-POLARISABLE ELEC- 

 TRODE. 



Zinc wire. 



-Clay plug in small glass 

 tube. 



-Zinc sulphate solution. 



FIG. 8. SANDERSON'S PATTERN OF NON-POLARISABLE ELECTRODE. 



