CONNECTED WITH THE BEAT OF THE MAMMALIAN HEART. 
185 
The unfavourable combinations were :— 
Left hand and left foot. 
Left hand and right foot. 
Right foot and left foot. 
Mouth and right hand. 
At that time I could not see the reason of this difference, and was surprised to find 
it so. There was, for instance, no apparent reason why a lead-off from mouth and 
right hand should be ineffectual, while a lead-off from mouth and left hand should be 
attended with a marked variation. And it was the most common and easily verified 
case. One electrode kept in the mouth while the other dips into a basin of salt 
solution, into which first the left hand then the right band is plunged, yields a ready 
demonstration of a favourable in contrast with an unfavourable lead-off. Another 
illustrative contrast is furnished by leading off from hands and feet. If the right 
hand and either of the two feet be led off', a marked electrical variation is manifested 
at each pulsation of the heart; if now the left be substituted for the right hand, no 
variation is apparent, or at most a slight one. 
Deferring the further enumeration of cases, I may at once offer the explanation of 
these apparently anomalous results. 
The contraction of the ventricles is not simultaneous throughout the mass, but 
traverses it as a wave (at the present stage the direction of the wave of contraction 
is immaterial). Inequalities of potential, at different parts of the mass, are con¬ 
sequently established at the beginning and at the end of each systole. Or, to reverse 
the order of statement, the inequalities in question are proof of the passage of 
a wave of excitation. The distribution of these inequalities of potential is 
represented diagrammatically in fig, 5. 
These data being transferred to the entire body, as in fig. 6, we have the dark 
portion a, a, a . . . as the area in which the potential of A is distributed, and the 
light portion 6, 5, 6 ... as the area in which the potential of B is distributed. 
Electrical variations will be manifested when any two points a and h are led oft’; 
no electrical variations will occur when any two points a and a, or h and 6, on the same 
equipotential lifie, are led off; small electrical variations will be obtained when two 
points a and a, or h and 6, on difterent equipotential lines, are led off. 
This is precisely what has been demonstrated in the experiments given above. 
Points a, a, a . . . are represented by the left arm, the left leg, the right leg, the 
front of the body, and by the rectum, &c. Points h, h, h . . . are represented by the 
mouth, the eye, the right arm, and the back of the chest. And, if the reader will 
refer to the results given above, he will notice that variations have been observed 
when two dissimilar points {a and b) have been connected with the electrometer, 
while variations have been absent or faint when two similar points (a and a, or b and b) 
have been explored. The difference of result, when the mouth and the right hand 
MDCCCLXXXIX,.— B, 2 B 
