PHASES OF A SINGLE CONTRACTION. 459 



in the following wood-cuts are drawn with the Pendulum Myo- 

 graph. 



Du Bois-Reymoud draws muscle curves on the smoked surface 

 of a small glass plate contained in a frame, which is shot by the 

 force of a spiral spring along tense wires, and on its way breaks 

 the contact. The trigger used for releasing the spring sets a 

 tuning fork at the same time vibrating. 



SINGLE CONTRACTION. 



In response to a single instantaneous stimulus, such as the 

 making or breaking of an electric current, a muscle gives a mo- 

 mentary twitch or spasm, commonly spoken of as a single con- 

 traction, which is of so short duration that without the graphic 



FIG. 185. 



Curve drawn by a frog's gastrocnemius on the Pendulum Myograph. 

 Below is seen the tuning fork record of the time occupied by the contraction. 

 Parallel to the hitter is the abscissa. The little vertical mark at the left 

 shows the moment of stimulation, and the distance from this to the begin- 

 ning of the rise of the curve gives the latent period, which is followed by 

 the ascent and descent of the lever. 



method of recording the motion we could not appreciate the 

 phases which are seen on the curve. 



The curve drawn on the recording surface of a pendulum myo- 

 graph, by such a single contraction, is represented in figure 185. 

 The short vertical stroke on the abscissa or base line is drawn by 

 touching the lever when the muscle is in the uncontracted state, 

 and indicates the time of stimulation. The upper curved line is 

 drawn by the lever and during the contraction of the muscle. 



In such a curve the following stages are to be distinguished : 



