MUSCLES AND MOTION 



87 



Directions. Touch the free end of the nerve with the 

 two electrodes. What happens to the muscle? Record the 

 extent of the action. 

 This shows that nerve 

 stimulation may cause 

 the muscle to move. 

 Keeping the electrodes 

 in contact with the nerve, 

 note whether the action 

 continues. Remove the 

 electrodes. What hap- 

 pens? Repeat this proc- 

 ess Several times and FlG - 42. Nerve Muscle Preparation: s, set 

 , , screw; c, clamp; /, femur; m, gastrocnemius; 



mark the distance that n , sciatic nerve; h, hook; Z, lever; e, elec- 



the lever moves each trodes; b ' battery - 

 time. Is it the same? Does the action increase or de- 

 crease? This result illustrates what may happen from over- 

 stimulation; namely, muscle fatigue. 



Repeat the experiment, applying the current to the body 

 of the muscle instead of the nerve. Compare with the re- 

 sults of the first experiment as to extent and strength of the 

 action. 



In both of the above experiments what property of the 

 muscle is stimulated? Why is muscle called contractile 

 tissue? 



LVI. STUDY OF LEVER ACTION (OPTIONAL). 



Apparatus. Wooden bar with holes near the ends and at the mid- 

 dle (exactly halfway between the end holes), spring balances. 



Directions. A. Support the bar by the middle hole (see 

 Fig. 43, A), and trim the bar till it balances level. Fasten 



