CONTRACTILE TISSUES 



453 



We have seen that the phenomenon is shown by voluntary muscle and by 

 nerve. The law applies also to the movements of plants (Burden-Sanderson, 

 1882, p. 42). 



Staircase. This phenomenon was also demonstrated by Bowditch (1871, 

 p. 669) in the frog's heart. Buckmaster (1886) found it in voluntary muscle and, 



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as we have seen (page 391), the local effect left behind by an inadequate stimulus 

 to nerve, as shown by Adrian and Lucas (1912), seems to be a similar condition. 

 This latter summation of inadequate stimuli ("summation of excitation," as it is 

 sometimes called) is shown by various muscular tissues and must be distinguished 

 from the summation of contractions observed in the superposition of tetanus, 

 where a contraction takes its start from a position of incomplete disappearance of 

 the one preceding it. 



