LABORATORY MANUAL OF PHYSIOLOGY. 



this compare with the muscle under isotonic conditions? Is any 

 muscle in the body, normally, under isometric conditions to any 

 extent ? 



XX. ELECTRIC PHENOMENA OF MUSCLE AND NERVE. 



1. Galvani's Experiment with Metals. Pith a frog. Evis- 

 cerate and remove everything above the urostyle and the last two 

 vertebrae. Remove the skin from both legs. Pass a hook, made 

 of clean copper wire, under both lumbar plexuses. Suspend the 

 preparation by the copper wire from a clean iron or steel rod. 

 Swing the preparation until some part of it comes in contact with 

 the rod. Result ? Explain. 



2. Contraction without Metals. Make a muscle-nerve prepa- 

 ration, cutting the nerve high up. Handle the nerve with a glass 



hook, allowing the nerve to 

 fall across the muscle. There 

 should be a twitch of the muscle 

 every time the nerve comes in 

 contact with it. This twitch 

 may be due to one of two things. 

 If the muscle is uninjured, and 

 the injured portion of the nerve 

 falls across it, the twitch may 

 be due to the completion of a 

 circuit between the injured and 

 uninjured portion of the nerve 

 itself, which are of different 

 electrical potentials. Or it may 

 be due to the completion of a 



FIG. 14. Secondary Contraction. s lt 

 Sciatic of first preparation ; J 2 , sciatic of 

 second preparation; w,, muscle of first 

 preparation ; z a , muscle of second prep- 

 aration ; e, electrodes. 



circuit between injured and un- 

 injured muscle through the 

 nerve. This is known as the current of injury or demarcation 

 current of muscle or nerve. 



3. Secondary Contraction. Make two muscle-nerve prepara- 

 tions. Allow the nerve of preparation 2 (see Fig. 14) to rest on 



[34] 



