TETANUS. 467 



of the lever, 'a second stimulation gives rise to 1J maximum 

 contractions, and so on, in various parts of the curve, a new 

 maximum curve is produced, arising from the point at which 

 the lever is when the second stimulus is applied (Fig. 190). 



During the latent period a second stimulation produces less 

 marked effect, and is difficult to demonstrate, but if the second 

 stimulus come after an interval of more than ^^ sec., summation 

 can be appreciated. 



This summation of effect also takes place when the stimulus is 

 insufficient to produce a maximum contraction, the succeeding 

 weak stimuli give rise to the same extent of contraction of the 



Fio. 190. 





Pendulum Myograph Tracings showing Summation. 1. Curve of maximum contrac- 

 tion drawn by first stimulus, the exact time of application of which is shown by the 

 small up stroke of the left hand of the base line. 2. Maximum contraction resulting 

 from second simple stimulation given at the moment indicated by the other small up 

 stroke. 3. Curve drawn as the result of double stimulation sent in at an interval 

 indicated by the distance between the up strokes, showing summation of stimulus and 

 consequent increase in contraction over the "maximum contraction." 



already partially contracted muscle, as if it were at its normal 

 length at the time of the second stimulation. The following 

 tracings (Figs. 191-193) show the effects of repeated stimulations 

 applied at the various periods indicated by the numbers on the 

 abscissa line. 



TETANUS. 



If a series of stimuli be applied in succession, at intervals less 

 than the duration of a single contraction, a summation of con- 

 tractions occurs, which results in the accumulation of effect until 

 the muscle has shortened to about one-half of the length it attains 

 during a single contraction, or about one-fourth the normal length 



