338 THE OUTGO OF ENERGY 



smoked paper below the recording levers. Stim- 

 ulate the muscle with a maximal break current 

 first through one pair of electrodes and then 

 through the other. In each of the resulting 

 curves measure the interval between stimulation 

 and contraction (for method see page 184). 



This interval will be longer when the muscle 

 is stimulated farther from the portion the con- 

 traction of which is recorded. The difference is 

 the time taken by the excitation to traverse the 

 part of the muscle lying between the two pairs 

 of electrodes. Measure the distance and calcu- 

 late the speed of the excitation. 



The nature of the excitation process is un- 

 known. The current of action has been shown 

 to precede the visible change in form of muscle. 

 It is usually assumed to be a manifestation of the 

 excitation process, but the precise relation be- 

 tween the two has never been ascertained. The 

 speed of the excitation is the same as that of the 

 contraction wave. 



The Contraction Wave. Remove from a CU- 

 rarized frog the long parallel-fibred muscles ex- 

 tending along the inner side of the thigh from 

 the pelvis to the tibia. Let the preparation rest 

 horizontally on a glass plate supported on a stand. 

 With fine wire fasten near the axle of each of 

 two heart levers a small piece of cork into which 



