On Electrical Stimulation of the Frogs Heart. 465 



induced ventricular, except when stimulation falls before the maximum 

 of ventricular systole, in which case there is usually a regular sequence 

 of auricular and ventricular contraction (fig. 8, c). 



Usually after the maximum of ventricular systole stimulation 

 causes a reduplicated beat with short latency, inside of which curve 

 falls that of the induced auricular contraction; however, genuine 

 sequential reduplication of auricle and ventricle with long latency 

 is not uncommon. Not unfrequently, after repeated stimulation of 

 the sinus, the heart assumes a new rhythm, which may be twice as 

 rapid as it was originally, and though omission of the alternate beat may 

 still be produced by stimulation at the time already indicated, the organ 

 returns again to its accelerated pace. In time, if stimulation be with- 

 held, the rhythm lapses again into the normal. The auricle shares in 

 the ventricular excitement (fig. 9). 



Fig. 9. 



Khythm which lias been changed by repeated stimulation of Sinus returning to 



normal. 



The Effect of Cold on the Feog's Heart. 



In these experiments the animal was placed upon a wire gauze 

 grating, and covered with a small bell- jar. Underneath the grating 

 and around the bell-jar was placed ice, so as to surround the frog, 

 which was kept in this position for an hour or longer. When its 

 movements had become slow and torpid it was killed, without loss of 

 blood, and placed on the cardiograph, already descr ibed, the tempe- 

 rature in the vicinity being kept low by means of blocks of ice placed 

 on the metal bars supporting the animal. The apparatus was 

 employed in the same manner as in our observations on the effect of 

 electrical stimuli on the normal heart, and the same order was observed 

 in recording the results. 



Effects of Electrical Stimulation of the Ventricle — Minimal Stimuli. 



The contraction of the chilled frog's heart, as is well known, lasts 

 for longer time than in the ordinary condition. When minimal 

 stimuli are applied to the ventricle (fig. 10) it is found that there is 

 a distinct refractory period, extending from the beginning of systole up 



