102 



records a horizontal line parallel to the abscissa. When the 

 current is shut off the descent is very steep at first, and 

 towards the end very slow. 



The number of shocks required to produce tetanus de- 

 pends on the animal, the muscle, and the condition of the 

 latter ; the more fatigued a muscle is the more slowly it con- 

 tracts, and therefore, the more readily does fusion of contrac- 

 tions take place. A fresh frog's gastrocnemius requires about 

 27 to 39 shocks per second to produce tetanus. 



Replace the key in the primary circuit by a metronome ; 

 connect the wires with the primary coil. Vary the rate of 

 vibration of the metronome and observe the effect on the 

 muscle curve. Compare with the previous tracings. 



XXVII 



347. Influence of Temperature upon the Contrac- 

 tion OF Muscle. Prepare a gastrocnemius muscle, leaving 

 it attached to the femur. The sciatic nerve may be disre- 

 garded. Fasten the femur in the clamp on the under side of 

 the cover of the " muscle warmer." Tie the end of a fine cop- 

 per wire around the tendon of Achilles. Bring the other end 

 of the wire through the. opening in the bottom of the muscle 

 warmer and bend the wire around the muscle lever, making 

 sure that the wire connecting the tendon with the muscle 

 lever is vertical. Connect the end of the fine copper wire 

 with one of the binding posts of the secondary coil. Connect 

 the other-post of this coil with the binding post on top of the 

 cover of the muscle warmer. Connect the battery with a 

 make and break key to the binding posts of the primary coil 

 of the inductorium for single induced shocks. Fill the outer 

 chamber of the muscle warmer with crushed ice. Bring the 

 writing point of the muscle lever againt a smoked 4rum and 

 let- the drum revolve at a fairly rapid speed. Insert a ther- 

 mometer in the top of the muscle warmer and stimulate the 

 cooling muscle at intervals of 5 degrees with a maximal break 

 current. As the temperature falls, the contraction curve be- 

 comes longer and the muscle shows a tendency to contracture. 

 Indicate the temperature upon each curve made. 



