STUDY OP A FROG S MUSCLE 



279 



Fig. 122 — Nerve endings in striated 

 muscle fibers. 



ultimately they end in the walls of the muscle fibers them- 

 selves. The large thread, with its branches, is a nerve, and 

 in the living frog the large end is continued backward to 

 the spinal cord through which 

 it connects with the brain. If 

 we remove all the muscles from 

 the leg of a freshly killed frog, 

 except the gastrocnemius, then 

 arrange such an apparatus as 

 shown in Fig. 123, and bring the 

 two ends of an electric circuit 

 in contact with the nerve, the 

 muscle will suddenly shorten and 



then relax again as though the frog were alive. If now 

 we remove the ends of the wires from the nerve a second 



contraction and relaxa- 

 tion takes place. Evi- 

 dently the shock of 

 making and breaking 

 the electric current is 

 transmitted by the nerve 

 to the muscle fiber and 

 acts as a stimulus to 

 the contractile sub- 

 stance which it con- 

 tains. Furthermore, the 

 experiment shows us 

 that a stimulus, such 

 as was given by the 

 electric current that we 

 sent over the nerves to the fiber, is sufficient to set in con- 

 traction at one time all the muscle fibers of such a mass. 



Pig. 123 — Nerve muscle preparation ; s, set 

 screw ; c, clamp , /, femur ; m, gastrocne- 

 mius muscle ; ?i, «, sciatic nerve ; A, liook ; 

 I, lever ; e, electrodes ; b, battery. 



