EFFECT OF ELECTRIC STIMULATION 319 



Extra Pulsation due to Induction-Shock 



In the case of cardiac tissue it is known that the excita- 

 biHty is least at the commencement of systole. A moderate 

 stimulus applied at this period induces hardly any effect. 

 During the occurrence of diastole, however, excitability is 

 relatively great. Hence, if stimulus be applied at diastole, 

 it is followed by an extra contraction. 



Turning to Desmodium, I find that similar characteristics 

 obtain in this case also. The application of stimulus at the 

 beginning of the contractile movement, which corresponds to 

 systole, has little or no effect. But during the movement of 



Figs, 162, 163. — Extra pulsation induced by induction-shock applied 

 at diastolic phase. 



relaxation, which corresponds to diastole, the application of 

 an induction-shock induces the arrest of relaxation and 

 gives rise to an extra or interpolated pulsation. I give 

 here two records, out of many, obtained from two different 

 specimens, in both of which a momentary electrical shock 

 was applied about the middle of the phase of diastolic 

 relaxation. The arrest of relaxation, and reversal to the 

 opposite phase of contraction, giving rise to an extra pulse, 

 are here clearly seen in both cases (figs. 162, 163). 



Effect of Transmitted Excitation on Pulsation 

 OF Desmodium 



On exciting the nerve that goes to the heart, two opposite 

 effects have been observed. In some cases there is induced 



