THE PHENOMENON OF CONTRACTION. 



43 



ing a total shortening greater than can be obtained by a single stim- 

 ulus (see Fig. 20). The extent of the summation in such cases 

 varies with a number of conditions, such as the intervals between the 



Fig. 19. — Analysis of tetanus. Experiment made upon the gastrocnemius muscle of a 

 frog to show that by increasing the rate of stimulation the contractions, at first separate 

 (1), fuse more and more through a series of incomplete tetani (2, 3, 4) into a complete tetanus 

 (5) in which there is no indication, so far as the record goes, of a separate effect for each 

 Stimulus. 



stimuli, the relative strengths of the stimuli, the load carried by the 

 muscle, etc. Taking the simplest conditions of a moderately loaded 

 muscle and two maximal stimuli, it is found that the greatest sum- 



