12 



SIR THOMAS LEWIS 



Fig. 3 A and B. When the heart is stimulated at its epicardial surface (Fig. 

 3B), contacts placed in line with the point stimulated show first of all an elec- 

 trical relation which is indicated by the large + and signs. This reaction of the 

 contacts is explained alternatively by the hypotheses of distributed and limited 

 potential differences (see small -)- and signs of the diagram). In this example 

 the distribution of potentials in the muscle and under the contacts is consistent, 

 irrespective of the hypothesis chosen. A, C and D : The heart is stimulated at 

 its endocardial surface and the potential difference recorded by the contacts 

 is at first in one direction (phase 1) and later becomes reversed (phase 2). 

 The supposed potential differences in the muscle, during the second phase, are 

 consistent with what is found at the contact points, irrespective of the hypothesis 

 adopted; but this is not so for the first phase; in this the hypothesis of limited 

 potential differences is alone consistent with observation. 



