MUSCLE AND NERVE 



43 



and completely fused. This fusion of single contractions eventually 

 gives rise to a tetanus. 



4. Compound Contraction or "Tetanus." Connect in series two 

 dry cells, a simple key, and posts 1 and 3 of the inductorium. Change 

 the gears of the kymograph so as to obtain the slowest possible speed 

 of rotation. Use a moderate strength of current and stimulate the 



FIG. 21. FUSION AND TETANUS. 



<S, Summation; F, fusion; T, tetanus. Time in seconds. The individual make and 



break shocks are repeated so quickly that a continuous contraction is obtained. 



muscle during a period of ten seconds. Compare this curve with the 

 one obtained previously. Since the tetanic contraction is the result of 

 the summation and fusion of simple twitches, it is much higher and 

 longer than a twitch. If long continued, the height of the curve de- 

 clines slowly, owing to fatigue. 



FIG. 22. TETANIC CONTRACTION. 



Recorded by means of Neef's automatic interrupter. Time in seconds. The decline 

 of the curve is an indication of fatigue. 



5. Relation of the Strength of Stimulus to the Height of Contraction. 

 Prepare a gastrocnemius muscle and fasten the femur in the clamp. 

 Connect the tendon with the writing lever, and put a 10-gram weight 

 into the scale pan. Record the abscissa. Retain the writing lever in 

 this line by means of the after-loading screw. Apply the electrodes 

 firmly to the upper part of the muscle. Push the secondary coil of the 

 inductorium over the primary. Record the make contraction, keeping 



