14 SIR THOMAS LEWIS 



first case the general direction in the body will be from right to left 

 throughout the whole excitation of the ventricle ; in the second case, 

 it will be for a brief period from left to right, and eventually from 

 right to left. The experiment affords the general condition illustrated by 

 the straight and bent muscle strips of Figure IB and D. The result 

 of this experiment is instructive. Stimulate the epicardial surface and, 

 from the first, contact Z is negative to contact C. This finding is con- 

 sistent with both hypotheses, the potentials being distributed as shown 

 in Figure 3 B and in Figure 4. 4 Stimulate the endocardial surface 

 (Fig. 3 C and D) and the curve has two opposite phases, a short first 

 phase during which contact C is negative to contact Z, and a longer sec- 

 ond phase during which contact Z is negative to contact C (Fig. 4). 

 This finding is consistent with one of our hypothesis only, namely, 

 that of limited potential differences. The association between the set 

 of the current and the direction in which the excitation wave moves 

 will be noted in this illustration. It constitutes a single and new illustra- 

 tion of an association which I believe to be firmly established and of 

 which numeious examples have already been published. 5 It was because 

 I found this association constantly to exist in the normal heart beat of 

 amphibians, reptiles, birds and mammalia, classes in which the spread 

 of the excitation wave is very diverse, that I first recognized the 

 hypothesis of distributed potentials to be untenable, for it is incon- 

 sistent with this association, as the diagrams clearly show (Figs. 3 

 Cand D). 



It may suffice at the present time if a few of the simpler illustrations 

 are cited. The first of these permits the display of some important 

 fallacies. It is the instance of the normal amphibian heart beat. The 

 amphibian heart ( Fig. 5 ) comprises not only sinus, auricle and ventricle, 

 but also a bulbus arteriosus. It is on hearts of this or of a closely allied 

 type, that almost the whole of the preliminary explanations of the 

 electrocardiogram have been based ; and it is with the mistaken inter- 

 pretation of these curves, and the hypotheses derived from them, that 

 we have today chiefly to contend. In this early work the heart was 

 examined by placing on the base and apex of the ventricle two contacts 

 and connecting them to a galvanometer. Because in such curves as were 

 regarded to be typical, the first deflection indicated relative negativity of 

 the base, it was concluded that the base first becomes active ; it was 

 further concluded that the excitation wave spreads as a simple wave 

 from base to apex. Now, further and closer observation by modern 



4. In stimulating the epicardial surface the curve is not usually expressed 

 as a single phase. It rises a little, hangs or falls away as the endocardial lining 

 is approached, and then rises steeply to yield the chief deflection which repre- 

 sents rapid involvement of a large mass of the ventricular substance. 



5. Phil. Tr. Roy. Soc., B. 207:221, 1916. 



