512 Dr. A. D. Waller. Various Inclinations of the [Mar. 6, 



two feet may be treated as negligible ; but by reason of the greater aeuteness 

 of the angle subtended by the E and L leads at the inferior lead F, as com- 

 pared with the superior lead M, a new factor must be introduced into the 

 formula, which is now taken as tana = 2 (E — L)/(E + L), where E and L 

 represent respectively observed magnitudes of the potential differences in the 

 right and left lateral leads. If, for example, the values have been observed, 

 E = 12, L = 4, then 



Put into words, the general conclusion expressed by the two formulae* for 

 calculating the direction of the cardiac current-axis from the right and left 

 potential difference existing at the outset of systole above and below the 

 heart, is as follows : — The tangent of the angle formed by the current-axis 

 with the vertical is proportional to the difference between the potential 

 differences of the strong lead and the weak lead divided by the sum of these 

 two differences. 



The error of angle by error of measurement of the spike is, with most 

 records, inconsiderable, except in the case of the left lateral lead, when its 

 direction is doubtful. When it consists of a small positive followed by a 

 large negative peak we may hesitate whether to take into our formula the 

 small positive or the large negative value ; in such case of doubt it is 

 advisable to calculate the angle for both values. If, in a doubtful case, the 

 right lateral is smaller than the transverse spike, the negative value of the 

 left lateral should be taken in the formula ; if the right lateral is larger than 

 the transverse, the positive value of the left lateral should be taken. But 

 I do not attach much value to the numerical result in such a case (vide infra 

 fig. on p. 520, the case of Dr. E.). 



In most normal records, where the ventricular spike is clearly positive, 

 there is no difficulty in measuring out its values for the right and left hands. 

 I have not taken into reckoning the small preliminary negative movement 

 (" Q ") by which the positive movement is more or less distinctly preceded. 

 This negative movement, while forming part of the systolic change of 

 potential, occurs before the ventricle has begun to contract. 



As far as it is possible to judge from simultaneous records by the E and L 

 lateral leads, taken on a film travelling at the rate of 130 mm. per second, 

 the two spikes E and L, when both are positive, culminate synchronously. 



* The two formulae might have been expressed by a single general formula, as follows : 

 tan = cot 6 (S - W)/(S + W), where 6 stands for the angle taken at M or at F, and S, W 

 for the values of strong and weak leads respectively. But the two special formulae are 

 preferable for practical calculations with a conventional direction of currents. 



