MUSCLE 



229 



applied, it is found that a series of simple contractions, each 

 with an interval of 0-05 of a second between them, is pro- 

 duced (fig. 114 (1)). If the stimuh follow one another at 

 the rate of 10 per second, a series of simple contractions is 

 still produced, but noAV with no interval between them. 



(2) If stimuli be sent more rapidly to the muscle, say at 

 the rate of 12 per second, the second stimulus will cause 

 contraction before the contraction due to the first stimulus 

 has entirely passed otF (fig. 114 (2)). The second contrac- 

 tion will thus be superimposed on the first, and it is found 

 that the second contraction is more 

 complete than the first, and the 

 third than the second. But, while 

 the second contraction is markedly 

 greater than the first, the third is 

 not so markedly greater than the 

 second, and each succeeding stimu- 

 lus causes a less and less increase 

 in the degree of contraction, until, 

 after a certain number, no further 

 increase takes place, and the degree 

 of contraction is simply maintained. 

 When the contractions follow one 

 another at such a rate that the 

 relaxation period of the first con- 

 traction has begun, but is not com- 

 pleted, before the second contraction takes place, 

 attached to the muscle, and made to write on a 

 surface, produces a toothed line. The contraction is not 

 uniform, but is made up of alternate shortenings and 

 lengthenings of the muscle. This constitutes " incomjdete 

 tetanus" (fig. 114 (2)). 



(3) If the second stimulus follows the first so rapidly 

 that it reaches the muscle before the contraction period has 

 given place to relaxation, then the second contraction will be 

 superimposed on the first, the third on the second, and so 

 on continuously and smoothly without any relaxations, 

 and thus the lever will describe a smooth line, rising at 

 first rapidly, then more slowly, till a maximum is reached 



Fig. 114.— Effect of a series of 

 Stimuli onSkeletalMuscle. 

 (See text.) 



a 



lever 



movmo- 



