XI. Electricity as a stimulus. The galvanic current. 



/. Appliances. Operating case; 3, 10 cm. pieces of uncov- 

 ered copper wire; a piece of zinc; beaker; a Daniell 

 cell; kymograph; myograph; simple contact key; 4 cov- 

 ered battery wires; 2 frogs. 



2. Preparation. 



(1) Curarize a frog. 



(2) To prepare a " water element ," take a small bright 

 piece of zinc, wind one end of a 10 cm. piece of cop- 

 per wire around it, remove the glass plate from the 

 middle clamp of the myograph, clamp two copper 

 wires so that one or two centimeters of wire will ex- 

 tend out horizontally on one side of the clamp, while 

 the other longer ends extend out on the other side; 

 one of these is wound around the piece of zinc. Bend 

 these long ends down to the perpendicular. Do not 

 allow these wires to touch each other in any part of 

 their course. 



(3) Charge the Daniell cell (See Appendix A-4), insur- 

 ing the proper amalgamation of the zinc. Do not put 

 the zinc into the cup until the cell is to be used. 



j. Experiments and Observations. 



(1) Take two coins of different metals, preferring cop- 

 per and silver. With a knife or file brighten on the 

 circumference of each two small surfaces removed 

 from each other by \ to \ the circumference. Touch 

 each coin separately to the tongue. Now bring the 

 two coins into close contact at bright points, leaving 

 the other two fresh surfaces in such a position that 

 the tongue may touch both at the same time. Touch 



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