ON THE EFFECT OF ELECTEICAL STrMU- 

 LATION OF THE FROG'S HEART, AND ITS 

 MODIFICATION BY HEAT, COLD, AND THE 

 ACTION OF DRUGS. 



In conjunction with THEODOEE CASH, M.D. 



(Eeprinted from the Proceedings of the Hoyal Society, vol. xxxv, p. 455, 



No. 227, 1S83.) 



Keceived May 16, 1881, read June 16, 1881. Eevised June 13, 1883. 



In the following research we have examined the effect of elec- 

 trical stimuli applied to the different cavities of a frog's heart, 

 and the modifications of their effect by heat, cold, and the 

 action of strychnia. The effect of electrical stimuli upon the 

 ventricle, and the alterations occasioned in it by the applica- 

 tion of heat, have already been studied by Professor Marey. 

 The time relations of excitation in the frog's heart have also 

 been very exactly determined by Dr. Burden Sanderson and 

 Mr. Page. But it seemed desirable to extend the scope of the 

 research, and instead of confining ourselves like previous ob- 

 servers to the effect of stimulation applied to the ventricle 

 alone, to observe also the effect of stimulation of the ventricle, 

 auricle, and venous sinus, both on the ventricular and the auri- 

 cular contractions. This we did with the hope that from such 

 series of observations we might be able to arrive at some con- 

 clusions regarding the transmission of stimuli from one part of 

 the heart to the other in the ordinary course of the circulation. 

 Professor Marey found that when an electrical stimulus was 

 applied to the ventricle of a pulsating frog's heart the effect 

 differed according to the condition of contraction or relaxation 

 in which the ventricle was at the time the stimulus was applied. 

 During the first part of the contraction of the ventricle, from 

 the commencement of the contraction until nearly its maximum, 

 stimulation had no apparent effect at all, and this period Marey 

 terms the " refractory period." Following this phase is a second 



