ELECTROCARDIOGRAM 15 



methods has shown that the first of these conclusions is usually incor- 

 rect, and that the last conclusion is never true. These early observations 

 on the cold-blooded heart and the conclusions derived from them are 

 open to serious criticism. The direction of the first deflection does not, 

 in point of fact, always indicate primary negativity of the base. The 

 direction depends largely in a given animal on the point chosen at the 

 base for examination ; there is also much variation from animal to ani- 

 mal. Later observations have shown that sometimes a basal point is 

 active before the apex; sometimes it becomes active after the apex 

 (Fig. 5) ; sometimes certain points at the base are activated before, and 

 certain points after, the apex. In all cases the base and apex are acti- 

 vated within a very short time interval of each other. The excitation 

 first reaches the surface of the heart at neither base nor apex, it reaches 



osob 



Fig. 5. Outline diagrams of the hearts of Bufo vulgaris major, showing 

 a number of surface readings expressed (in decimal points of a second) 

 to the beginning of R in an axial lead. Toad A, an unpublished figure, 

 showing that the base is activated earlier than the apex. Toad E (after the 

 original figure) showing that the apex is activated earlier than the base. In 

 both cases the central region of the ventral surface is activated earliest of all. 

 In the axial electrocardiogram of each animal the chief deflection was an 

 upright R; in the case of toad E, the electrocardiogram also showed a prominent 

 S wave. 



the central portions of the ventricle (Figs. 5 and 6 A) and races 

 simultaneously up to the base and down to the apex; the race may be 

 won in one other direction ; usually it is won at the apex. It is easy to 

 understand why these base-apex curves of early days often seemed to 

 indicate primary negativity of the base. The extreme base does become 

 active a little before the apex in some amphibian hearts, though that 

 is not the rule. If the extreme apex is chosen for one contact, and a 

 point somewhat removed from the base is chosen for the second, and 

 this would be the natural tendency 8 of experiment, primary negativity 



6. The tendency being to allow an interval of lesser or greater extent between 

 the contact and the A-V junction. 



