598 



ELECTRICAL STIMULATION OF THE FROG S HEART. 



two- fifths of a second, and thereafter during the subsidence of 

 the ventricle, the period of latency rapidly diminishes. The 

 most perfect beat of reduplication is produced by stimulation 

 at the commencement of systole, or after relaxation of the 

 ventricle. 



Stimulation of the Auricle — Minimal. 



It is but rarely that we see a refractory period whilst apply- 

 ing minimal stimuli to the auricle. Usually, stimulation at all 

 times causes a reduplicated beat, the auricular reduplication 

 preceding that of the ventricle in the usual rhythm. On 

 stimulation, an auricular systole is produced, and not until this 

 movement has reached the usual point does the ventricle com- 

 mence its systole (Fig. 188). 



Fig. 188. 



Stimulation of Auricle (minimal). 



Stimulation of the Auricle — Maximal. 



There is no refractory period. Occasionally the stimulus 

 falling at the very commencement of the ventricular systole 

 will cause inhibition or coincidence of the following beat, or it 

 may cause a reduplication with a latency of about one second 

 (Fig 189). 



Fig. 189. 



Stimulation of Auricle (maximal). 



