iv ELECTROMOTIVE ACTION IN MUSCLE 897 



right ventricle was still beating feebly, the time-difference was 

 -^ sec. The same was demonstrated again by Nuel on the frog's 

 heart. On the dog he was able, by the physiological rheoscope, 

 to demonstrate that the contraction of the auricle is accompanied 

 by as marked an electromotive variation as that of the ventricle, 

 and that the time -difference between the two electromotive 

 processes corresponds entirely with the contraction of the two 

 cardiac sections. 



In order to ascertain more exactly the time-relations and 

 form of the electromotive variation (the " excitatory wave ") 

 which accompanies activity in cardiac muscle, experiments were 

 undertaken almost at the same time by Engelmann (34) and 

 Marchand (35) on the frog's heart, with Bernstein's rheotome. 

 The ventricle, which had been quieted by the removal of the 

 auricle, was stimulated either at its base or apex by a single 

 induction shock ; whatever the situation of the lead-off from the 

 surface of the ventricle, or the alterations in its length, and 

 distance from the point of stimulation, the first effect was invari- 

 ably a current directed in the heart away from the seat of 

 excitation. The rheotome is indeed superfluous in this connec- 

 tion. The galvanometer circuit may be permanently closed ; with 

 a sufficient length of tract led off, and moderate sensitivity of 

 galvanometer, the first effect of the stimulus in every case is a 

 deflection of the scale in the given direction. Accordingly, each 

 portion of the ventricular muscle must, during excitation, become 

 temporarily electromotive in a negative direction, which nega- 

 tivity (as also contraction, according to Engelmann) is propagated 

 from the seat of excitation, wherever this is situated, in all 

 directions through the ventricle. With the rheotome it may 

 further be shown that on leading off" from the external surface of 

 the ventricle by two points that give no current during rest, and 

 are at unequal distances from the seat of excitation, the electro- 

 motive response of the heart corresponds as a rule with that of 

 normal, striated, parallel-fibred muscle led off from two longi- 

 tudinal surfaces ; i.e. a diphasic variation usually makes its appear- 

 ance, and that of such a kind that the point nearest to the seat 

 of excitation is at first negative, and then positive, to the more 

 distant point (Fig. 126). 



In an equal number of cases, however, the second (positive) 

 phase is wanting, and either the initial state of indifference 



5 



