Electromotive Phenom. of the Mammal. Heart. 267 



We must nevertheless bear in mind that it is quite possible that 

 there is really an electrical change at the base preceding that at the 

 apex under all circumstances, but that it develops in some cases so 

 slowly that no appreciable movement of the electrometer is caused by 

 it before the development of the large E. M. F. of the warmer apex 

 comes to swamp it; that is to say, that the state of excitation of the 

 muscular elements at the base, is sufficient to excite adjoining elements 

 and thus be propagated along the ventricle before it has attained suf- 

 ficient intensity to cause the slightest movement of the mercury menis- 

 cus of the electrometer. 



To return to the normal curve for a moment. It will be noticed 

 at once how different is the appearance of our curve from that of 

 those obtained by Sanderson and Page from the frog and tortoise; yet 

 on consideration we shall see that this difference lies merely in the 

 duration of the electrical change. In the frog's heart, if we lead off 

 from two points, a and h at apex and base respectively, each contraction 

 is attended by a double variation, the two phases of which are sepa- 

 rated by an equipotential interval. At the commencement of each 

 beat, h becomes negative to a, and the meniscus makes a rapid move- 

 ment towards the point (if the base electrode be connected with. the 

 acid); m a short time the contraction reaches a, so that the negati- 

 vity at a and h is equal; this is equivalent to putting on an E. M. F. 

 equal and opposite to the first E. M. F., and the mercury returns 

 rapidly to the position of zero potential-difference, so causing what 

 Dr. Sanderson calls a „spike". So long as the ventricle remains con- 

 tracted as a whole, the meniscus remains in tMs position; but when 

 relaxation begins at the base there is again a difference of potential 

 between a and h — a now becoming negative to h for a short time, 

 and producing a movement of the meniscus stays from the point; and 

 there being no opposing E. M. F. to bring it back, the return of the 

 meniscus to zero is slow; for, the electrometer having to discharge it- 

 self through the high resistance of the electrodes and tissues, it fol- 

 lows its characteristic logarithmic curve i). 



Burch, Proc. Roy. Soc. Vol. 48. p. 91. 



