On Electrical Stimulation of the Frog's Heart. 455 



On the Effect of Electrical Stimulation of the Frog's Heart, 

 and its Modification by Heat, Cold, and the Action of 

 Drugs." By T. Lauder Brunton, M.D., F.R.S., and 

 Theodore Cash, M.D. Received May 16, 1881. Read 

 Jane 16, 1881. Revised June 13, 1883. 



In the following research we have examined the effect of electrical 

 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 application 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. Burdon Sander- 

 son and Mr. Page. Bnt it seemed desirable to extend the scope of 

 the research, and instead of confining ourselves like previous observers 

 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 auricular contractions. This 

 we did with the hope that from such series of observations we might 

 be able to arrive at some conclusions 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 

 offect 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, stimu- 

 lation had no apparent effect at all, and this period Marey terms the 

 ** refractory period." Following this phase is a second one, to which 

 we have given in the following paper the term of the " sensitive 

 phase," lasting from the maximum of systole to its end. The refrac- 

 tory period varies in duration according to the intensity of the 

 stimulus, and the conditions under which the heart is operated upon. 

 The feebler the stimulus, the longer is the refractory period. When 

 the stimulus is very slight the refractory period may persist during 

 the whole ventricular systole ; as the stimulus is increased, the refrac- 

 tory period becomes shorter, and finally, when it is very strong, 

 disappears altogether. 



Heat applied to the heart shortens the refractory period or abolishes 

 it altogether. Cold has an opposite effect, and lengthens the refrac- 

 tory period. The contractions caused by artificial stimulation do not 

 much alter the cardiac rhythm, for the accelerated beat is followed 



