89 



once thrown into a state of rig-id spasm or continuous con- 

 traction called tetanus. Compare this tracing with that of 

 (a). This form of stimulation is known as the interrupted cur- 

 rent or repeated shocks. 



324 Electricity itself is not readily conveyed through 

 the nerve, but the irritation caused by it, generates a stimulus 

 which is transmitted, Ligate the nerve by tying tightly 

 around it a piece of thread. Stimulate the nerve as before ; 

 there should be no result, as the ligature has crushed the 

 nerve and blocks the passage of the stimulus. Scratch your 

 name on the above tracings to identify them. The tracings 

 may be made permanent by drawing the paper through a pan 

 of shellac. 



XXIII 



325. Secondary Contraction. Arrange the induction 

 apparatus for single make and break shocks. Pith a frog 

 and use the hind legs for nerve-muscle preparations, and ar- 

 range them upon a glass plate. Place the sciatic nerve of 

 the left leg upon the gastrocnemius muscle of the right leg, 

 fig. 20. Place the sciatic nerve of the right leg over the elec- 

 trodes and stimulate the nerve with single induction shocks 



Secondary 

 Contr'cLction' . 



Fig. 20. 

 Fig. 20, «, nerve ; m, muscle. 



