314 THE OUTGO OF ENERGY 



circuit may be made. By means of the induc- 

 torium, the muscle is stimulated at one end. 

 The galvanometer records the current of action 

 by means of electrodes placed at the other end 

 of the muscle. The position of the galvanometer 

 contact on the wheel can be shifted nearer to or 

 farther from the stimulating contacts ; thus the 

 interval between stimulation and the making of 

 the galvanometer circuit may be chosen at will, 

 and the electromotive force at any point in the 

 action wave registered. By repeatedly changing 

 the interval, the several portions of the wave 

 can be investigated successively, and the results 

 plotted. With Hermann's rheotachygraph, the 

 whole electrical change may be recorded at one 

 time. In this instrument the stimulating con- 

 tacts revolve rapidly, and the galvanometer con- 

 tact less rapidly, so that the interval between 

 stimulation and the closure of the galvanometer 

 continually alters. The effect of the electrical 

 change on the galvanometer is thus prolonged so 

 that the galvanometer mirror is able to follow it. 

 The results from these different methods agree 

 in showing that the electrical change sweeps 

 over the muscle (and nerve), in the form of a 

 wave at a rate, in frog's muscle, of about three 

 metres per second. The duration of the wave 

 is from 0.0033 to 0.0040 second. The ascent is. 



