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A TEXTBOOK OF PHYSIOLOGY 



stimulus. If, however, the first stimulus is not producing a maximal 

 contraction, then the second stimulus will add itself to the first, and 

 again a greater effest is obtained than would have obtained by either 

 separately. < 



Fu. 286. SUPERPOSITION OF Two SINGLE CONTRACTIONS. 



Each contraction is recorded alone by a break shock caused by opening a iixt-tl k< v : 

 both keys are then set, and the recording plate striking them open successively, 

 causes two stimuli and a summation of the two contractions. 



>'IG. 287. COMPOSITION OF TETANUS. (Waller.) 



Stimuli caused by a spring interrupting a primary circuit by vibrating in and out <>t 

 a mercury cup; the vibration frequency is increased by shortening the spring. 



