cold heart-stimulation of ventricle. 589 



The Effect of Cold on the Frog'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 described, the temperature in the vicinity being kept 

 low by means of blocks of ice placed on the metal bars sup- 

 porting 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 record- 

 ing 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. 176) it is 

 found that there is a distinct refractory period, extending from 

 the beginning of systole up to the last third of the summit of 

 the curve in the accompanying tracing, and persisting past the 

 maximum of systole. 



Fi&. 176. 



Stimulation of the Ventricle (minimal). Opening stimulation only effective 



It is, therefore, always longer than in the normal heart. 

 After the refractory period has passed, stimulation causes 

 reduplication of the ventricular beat. The later on in the 

 diastole that the stimulus falls the shorter is the latency. 



