4 ANIMAL ELECTRICITY. LECTURE I. 



positive plate, and A, the less active spot, where less 

 chemical action is going- on, the collecting or electro- 

 negative plate. 



Let me try to fix this point in your memory by 

 two elementary experiments, the first to specify the 

 direction of current by a typical voltaic couple (zinc 

 and copper), the second to identify w^ith such a current 

 the current of animal electricity that passes from more 

 active to less active tissue. 



ZINC 



COPPER 



jaVtwaterJ 



I iiiiiii I ii. ii ii 

 > 



Fig. 2. — A simple voltaic couple. 



The surface between zinc and fluid is the principal seat of chemical action. 

 Current in the cell is from zinc through fluid to copper. Through the galvan- 

 ometer it is from copper to zinc. 



Preliminary Experiment. — A slip of zinc and a 

 slip of copper dipping into a glass of salt solution 

 and connected with a galvanometer will exhibit the 

 character and direction of action of a representative 

 voltaic couple. The current will indeed be so large 

 that with this delicate instrument arranged as it is for 

 the far smaller currents generated in living nerve, we 

 must "shunt" it, i.e., only let a small fraction of it 

 pass through the galvanometer. 



