468 MANUAL OF PHYSIOLOGY. 



of the relaxed muscle ; it can then shorten no more no matter how 

 the stimulus be increased in rate or strength. As long as the 

 stimuli are continued, the various single contractions caused by 

 the individual shocks are fused together (Fig. 191) ; but if the 

 interval between the stimuli be nearly as long as the time occu- 



FIG. 191. 



Curve of tetanus resulting from 30 stimulations per second, drawn on a drum rotating 

 slowly compared with the motion of the Pendulum Hyograph. The stimulation com- 

 mences at " 30," and ceases just before the lever begins to fall. No trace of the individual 

 contractions of which the tetanus is composed can be recognized. 



pied by a single contraction, the line drawn by the lever will 

 show notches indicating the apices of the fused single contrac- 

 tions (Figs. 192 and 193). 



This condition of continuous summation of contractions is 

 called tetanus, and is said to be the manner in which muscular 



FIG. 192. 



Curve of tetanus composed of imperfectly fused contractions resulting from 12 stimu- 

 lations per second. The serrations on the left of the eurve indicate the individual con- 

 tractions. 



motion is produced by the action of the nerves in obedience to 

 the will. All the actions of our skeletal muscles are then made 

 up by the fusion of many single contractions into tetanus. 



With from twenty a second to upward of many hundreds of 

 induced shocks one can produce complete tetanus in a frog's 



