XIII. The effect of the induced current. 



/. Appliances. Operating case; inductorium with Neei 

 hammer; contact key; DuBois Reymond key; 7 wires; 

 1 Daniell cell; materials for making hand electrodes [2 

 No. 24 or 28 wires ^ meter long, 2 pieces of capillary 

 rubber tubing 4 or 5 cm. long, thread]; 2 frogs. 

 2. Preparation. (a) To make hand electrodes for use with 

 induced currents. Push a thin wire through a piece of 

 capillary rubber tubing (capillary glass tubing may be 

 used instead of the rubber), bring two such side by side 

 and wrap thread around them. If glass tubing be used 

 the wire will need to be fixed in the tubes with a drop of 

 sealing wax. 



Such a pair of hand electrodes are shown in Figure 9> 

 page 52. 



() Set up electric apparatus with contact key in 

 primary circuit and short-circuiting key in secondary 

 circuit. 



j. Operation. Make and mount gastrocnemius prepara- 

 tion. 

 4. Observations. 



(1) Take tracings of the contractions produced by a 

 series of " make, induction shocks " applied indirectly. 

 The " make, induction shock" is obtained as follows: 

 (a) With primary circuit not interrupted by the 

 Neef hammer, but closed and opened only by the 

 contact key; open the short-circuiting key of the in- 

 duced circuit. 



() Close the contact key of the primary circuit, a 

 make induction shock i. e., a shock in the in- 

 70 



