On Electrical Stimulation of the Frog's Heart. 473 



cation (fig. 21). Should stimulation fall at the commencement of 

 systole, the latency is long, nearly equal to the length of the beat ; 

 and the reduplication is very complete. 



Stimulation at the maximum of systole has a latency of about 

 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 applying 

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

 causes a reduplicated beat, the auricular reduplication preceding that 



Fig. 22. 



Stimulation of Auricle (minimal) . 



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 commence its systole (fig. 22). 



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. 23). 



Fig. 23. 



Stimulation of Auricle (maximal). 



The latencies are invariably long when the auricle is so stimulated 

 that its induced beat is a normal one and precedes the induced ventri- 

 cular systole in its normal rhythm. 



