622 ELECTRICAL STIMULATION OF THE FROG'S HEART. 



the normal heart stimulation in advanced diastole frequently 

 causes a spontaneous auricular and ventricular contraction, or a 

 ventricular beat preceding the auricular. 



In the heated heart we have noticed, in addition to the ex- 

 cessive diminution or abolition of the refractory period in the 

 ventricle already observed by Marey, that usually the refractory 

 period in the auricle entirely disappears. A single stimulation 

 of the ventricle sometimes gives rise to a series of contractions 

 with incomplete relaxation intervening. After this has occurred, 

 or after a simple reduplication has been caused, it often happens 

 that the auricular beat occurriiig in normal sequence is not 

 followed by ventricular, which seems to show a temporary state 

 of exhaustion of the ventricle. In the heated heart the dura- 

 tion of a systole is so short that two beats immediately succeed- 

 ing one another may be perfectly distinct, while, in the normal 

 heart, the second one would have fallen within the time of the 

 systole of the first, so that it could only have appeared, if it 

 were possible at all, as an increase either of the height or length 

 of the first systole. Inhibition occurs in the heated heart as 

 well as in the normal, which is most frequently observed upon 

 stimulation of the venous sinus, and it is frequently at this time 

 associated with a reduplicated auricular contraction. The effect 

 of strychnia is to prolong the refractory period of the ventricle. 

 Stimulation of the ventricle is frequently succeeded by con- 

 traction of the auricle. There is an increased tendency for 

 stimulation of the ventricle to induce a beat of the auricle 

 preceding the ventricular systole. There is less tendency for 

 the stimulation of the venous sinus or auricle to induce a beat 

 of the ventricle succeeded by one of the auricle ; and, indeed, 

 this only occurs when the stimulus falls just at the end of the 

 ventricular systole, i.e., when the ventricle itself is most sensi- 

 tive. These facts seem to indicate that the nervous channels 

 are more active in transmitting stimuli, both downwards from 

 the venous sinus to the auricle and ventricle, and from the 

 ventricle back to the auricle. 



In its effect upon the refractory period, and in the tendency it 

 produces to maintain the regular rhythm, the action of strychnia 

 agrees with that of cold, as shown in the present series of 



