ON THE EFFECT OF ELECTEICAL STIMULA- 

 TION OF THE FEOG'S HEAET, AND ITS 

 MODIFICATION BY COLD, HEAT, AND 

 THE ACTION OF DEUGS. 



In conjunction with THEODORE CASH, M.D. 



(Eeprinted from the Proceedings of the Royal Society, yol. zxxii, No. 214, 1881.) 

 Eeceived May 16, 1881. Read June 16, 1881. 



Feom the results of the recorded experiments conducted on the 

 frog's heart in its normal position and still exercising its circu- 

 latory function, we have found — 



I. That electrical stimulation by a single induced shock has 

 either an obvious effect on the contraction and rhythm of the 

 organ, or no such effect is apparent. 



II. That the effect is modified by — 



(a.) The Time of the Cardiac Cycle in which Stimulation Falls. 

 — Thus Marey has already shown that a so-called refractory 

 period is demonstrable under certain conditions.* Well-marked 

 variations in latency when the stimulation is potent to induce a 

 systolic contraction are to be recognised. 



(b.) The Strength of the Stimulation Applied. — Eefractory 

 periods possible under minimal stimulation can no longer be 

 demonstrated under maximal, whilst a disturbance of the rela- 

 tionship of auricular and ventricular contractions may be 

 induced. 



(c.) The Area of the Heart to which Stimulation is Applied. — 

 A refractory period demonstrable under stimulation of the ven- 

 tricle may cease to occur when the sinus venosus is the seat of 

 irritation. 



* The conditions of this refractory period, or "period of diminished excit- 

 ability," have been yery fully investigated by Dr. Burdon Sanderson and Mr. 

 Page. Froc. Boy. Soc, vol. xxi, p. 373. 



