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



all the three " favourable " leads : it is sufficient to compare the " good " hand 

 (left) with the " bad " hand (right) by taking the right and left superior leads. 

 And so I reduce my system of leads to five, as under: — 



I. Transverse. 



II. Eight lateral. 



III. Left lateral. 



IV. Eight superior 

 V. Left superior. 



Note. — In adopting this simplification we should, however, not lose sight 

 of the fact that, for certain finer determinations, the P.D. between the two 

 feet must be taken into reckoning, and that we may not always take as 

 equivalent axial with right lateral and equatorial with left lateral, although 

 for all ordinary purposes this may be done. Also, in the case of the mouth 

 leads, where we shall content ourselves with taking the left superior as the 

 strong lead and neglect the other two strong leads, viz., left and right inferior, 

 we may find it necessary to take into account the small differences that 

 obtain between the three strong leads with the mouth. An idea of their 

 order of magnitude is given by the following example, in which they were 

 carefully measured : — 



Eight superior 3 mm. (= 0-00023 volt) 



Left superior 15-3 „. (= 0-00118 „ ) 



Eight inferior 16*5 „ (= 0-00126 „ ) 



Left inferior 17"5 „ (= 0-00135 „ ) 



The study of the subject was subsequently taken up by Einthoven and his 

 pupils, whose principal publications appeared in 1895, 1900, and 1908. In 

 1900 he extended the inquiry to the abnormal heart. In 1903 he devised 

 his string-galvanometer, which, by reason of its superior rapidity, is preferable 

 to the capillary electrometer for these observations. At the same time, 

 Einthoven reduced the six possible leads from the extremities to three, and 

 promulgated what is known as " Einthoven's equation," viz. : — 



Lead II (axial)— Lead I (transverse) = Lead III (left lateral), 



and represented in the form of an equilateral triangle, of which the heart is the 

 centre. And quite recently* Einthoven has given a construction by which he 



* W. Einthoven, "TJeber die Form des menschlichen Elektrocardiogramms," 'Pfliiger's 

 Archiv,' 1895, vol. 60, p. 101 ; "W. Einthoven and K. de Lint, " tlber das normale 

 menschliche Elektrocardiogramm, und iiber die capillar-elektrometrische Untersuchung 

 •einiger Herz-Kranken," 1 Pfliiger's Archiv,' 1900, vol.80, p. 139; W. Einthoven, "Die 



