On Electrical Stimulation of the Frogs Heart. 



48a 



instantaneous auricular response, the ventricular reduplication occur- 

 ring 1"*3 after stimulation. 



In the case of maximal stimulation, the usual result is an instan- 

 taneous auricular systole succeeded by a ventricular. The latter, 

 therefore, has a latency equal to the auricular beat : this is seen in 

 I l9 T 2 , in both of which the latency is about *7 /; ; but in I 3 we have, on 

 the other hand, no auricular reduplication for l"'l. In both this 

 instance and H 1 stimulation occurred at the commencement of ven- 

 tricular systole. 



Time tracing. Electro-magnet recording seconds. Applicable to all tracings in 



Appendix A. 



Appendix B. Heated Heart. 



In some cases, heating a frog's heart through 4° "5 C. may fail to 

 obliterate entirely the period of resistance to stimulation. Heat, 

 however, in the same experiment may be shown to shorten the refractory 

 period much, and to limit it to the very commencement of ventricular 

 systole (in stimulation applied to the ventricle). The series of tracings 

 given were taken from a large specimen of Bana esculenta, which had 

 been kept at a low temperature for a considerable time before the 

 experiment. The tracing obtained at room temperature (K) is there- 

 fore that of a cold heart, and the refractory period extends up to the 

 commencement of relaxation after systole. After hot water had beeu 

 run through the support for 5', and the temperature raised about 

 2° C, we find diastole increased and systole much shortened; at the 

 same time there is a refractory period as extensive as in the cold 

 heart, that is to say, extending to the commencement of relaxation K . 



In K 3 after heat had been applied 10', and the temperature raised 

 another degree, stimulation at an earlier phase produces redupli- 

 cation. Heated still further, K 4 , there is reduplication at systolic 

 maximum, and at K 5 everywhere except at the very commencement 

 of systole. After heating through about 5° we still have a refractory 

 period, whilst the curve has been reduced from 1"'4 to '4". In many 

 cases, however, the same extent of heat may obliterate the refractory 

 period completely. The heart which yielded these curves passed into 

 rigor without showing the abolition. In the heated heart, of which 

 the ventricle is stimulated, we may find that the auricle does not in 

 any way participate in the ventricular excitement, but continues to 

 beat in its usual rhythm. Thus, when the heated heart yields a 

 series of contractions in answer to a single stimulation — a result not 

 unfrequently obtained — the auricle does not reduplicate, but may 

 vol. xxxv. 2 K 



