50 Dr. A. D. Waller. Various Inclinations of the 



equipotential lines at opposite ends of the heart. To-day I represent the angle 

 as 30° to the left (it can range in healthy subjects between 10° to the right 

 and 100° to the left), and draw straight equipotential lines, parallel with the 

 equator, at right angles to the current-axis CC (fig. 1). To-day as in 1889 

 I regard as essential the distinction between " strong " leads (left superior 



Eig. 1. — A typical heart with an oblique electrical axis, a — 30°. 

 OO is the equator, CC the current-axis. Equipotential lines drawn parallel to the 

 equator, and at right angles to the current-axis at regular intervals of l/10000th volt. 

 a indicates the " axial angle " formed with the vertical MF by the current-axis CC. 

 R — L 



tan a = 2 j— j- where B, and L are the electromotive values of the Eight and Left 

 inferior ventricular spikes. 



ML, and right inferior BF) and " weak " leads (right superior MR, and left 

 inferior LF) (see figs.). The present diagram (fig. 1) is drawn so as to exhibit the 

 relative values of potential'difference between the led-off points R, M, L, F, by 

 the number of equipotential lines which they include. Each unit = 1 x 10 -4 

 volt. Thus e.g. in fig. 1 it is to be seen that (approximately) MR = 1*5 ; 

 ML = 5-5 ; RL = 4-0 ; RF = 9-0 ; LF = 5-0 ten-thousandths of a volt. 



At pages 518-9* of the communication to which the present paper belongs 

 it is stated that a full consideration of the effects of respiration upon the 

 (amplitude of the) electrocardiogram is a necessary preliminary to the due 

 understanding of the physiological and pathological departures from the 

 * ' Eoy. Soc. Proc.,' B, vol. 86 (1913). 



