16 SIR THOMAS LEWIS 



of the base would usually be manifested; for the reason that a point 

 a little removed from the base is usually activated earlier than a point 

 at the extreme apex. The precise time relations of basal and apical 

 activity being unknown beforehand, this observation would naturally 

 be construed as indicating that the excitation wave starts at the base. 

 From this conclusion, false as it was, it was an easy step to the still very 

 prevalent general erroneous assumption that when, as is the rule, the 

 basal contact of an indirect lead (method of Fig. IB) first demon- 

 strates negativity, activity is confined to muscle which lies nearer to 

 this basal contact than to the apical one. Thus, in human electro- 

 cardiography it has frequently been assumed that R, the chief deflection, 

 is essentially a basal effect and that ^ is essentially an apical effect ; for 

 R represents relative negativity of the basal and S of. the apical contact. 

 Neither conclusion is justified. 



These assumptions, erroneous as I believe them to be, arise chiefly 

 from the idea that if muscle at the base is active, the basal contact will 

 show relative negativity and, conversely, that if the apex is active, the 

 apical contact will show relative negativity. These are views based on 

 the hypothesis of distributed potentials. A primary basal activity may 

 display itself in relative negativity of the apical contact as the experi- 

 ment illustrated in Figure 3A clearly indicates. The erroneous assump- 

 tions also arise, in part, because the base-apex curve of the amphibian, 

 where contacts are laid directly on the heart, has been assumed too 

 rigidly to be comparable with the curves from outlying contacts such 

 as are used in clinical electrocardiography. The difference between the 

 two methods is that in the first the curve chiefly expresses the potential 

 differences between two small areas, one at the base and one at the 

 apex; while in the clinical method the lead (when axial) is from the 

 whole of the basal and the whole of the apical parts of the heart ; the 

 clinical curves express the electrical changes in the entire mass of 

 cardiac muscle; the direct leads do not. The two methods are strictly 

 speaking incomparable (compare Figs. 1C and D from this point of 

 view). 



The axial electrocardiogram of the amphibian heart (Fig. 7), in 

 so far as it expresses spread of the excitation wave, consists of the 

 following deflections. 



1. A chief and primary deflection (R) indicating relative negativity 

 of the contact beyond the base. 



2. An inconstant second deflection (S) indicating relative negativ- 

 ity of the contact beyond the apex. 



3. A deflection (B), occurring at a late phase of the electro- 

 cardiogram, corresponding to activation of the bulbus arteriosus, and 

 indicating relative negativity of the apical contact. 



