CH. X.] THE MUSCLE- WAVE 119 



less by curare, if one end of the muscle is stimulated, the contraction 

 travels as a wave of thickening to the other end of the muscle, and 

 the rate of propagation of this wave can be recorded graphically. 

 The next figure (fig. 149) represents one of the numerous methods 

 that have been devised for this purpose. A muscle with long parallel 

 fibres, like the sartorius, is taken ; it is represented diagrammatically 

 in the figure. It is stimulated at the end, where the two wires, 

 + and , are placed ; it is grasped in two places by pincers, which 

 are opened by the wave of thickening ; the opening of the first pair 

 of pincers (1) presses on a drum or tambour connected to a second 

 tambour with a recording lever (I'), and this lever goes up first ; the 



FIG. 149. Arrangement for tracing the muscle-wave. (M'Kendrick.) 



lever (2') of the tambour connected with the second pair of pincers 

 (2) goes up later. If the length of muscle between the pairs of 

 pincers is measured, and by a time-tracing the delay in the raising 

 of the second lever is ascertained, we have the arithmetical data for 

 calculating the rate of propagation of the muscle-wave. It is about 

 3 metres per second in frog's muscle, but is hastened by warmth and 

 delayed by cold and fatigue. 



The Effect of Two successive Stimuli. 



If a second stimulus follows the first stimulus, so that the muscle 

 receives the second stimulus before it has finished contracting under 

 the influence of the first, a second curve will be added to the first, 

 as shown in the accompanying diagram (fig. 150). The third little 



