462 



Drs. T. L. Brunton and T. Cash. 



~No secondary contraction can usually be produced in the ventricle 

 till an induced auricular contraction has occurred ; and as the 

 auricular latency is considerable, the ventricular latency is also very 

 long. Thus, should the stimulus producing contraction fall at the 

 commencement of ventricular systole, the auricle may have a latency 

 of one second and the ventricle of 1'4 seconds. 



The sensibility of the auricle to minimal stimulation may generally 

 be divided into three phases : — 



lstly. Stimulation may fall at such a stage of auricular activity that 

 it does not cause an instantaneous response, but allows the auricle to 

 pass through its diastole before it causes reduplication. 



2ndly. It falls at such a time that the auricle responds instan- 

 taneously. 



3rdly. About or shortly after the period of auricular maximum, 

 stimulation may cause inhibition of the auricular and the ventricular 

 sequential beat. 



Stimulation at any period during the diastole of the auricle until 

 the abscissa is reached, causes a reduplication. The latency of this 

 reduplicated beat is shorter the further the diastole is advanced. It 

 is followed by an induced ventricular beat in ordinary rhythm. 



Stimulation during complete auricular diastole and before systole 

 commences causes a contraction with very short latency, succeeded by 

 ^n induced ventricular contraction. But it is to be noted that occa- 

 sionally stimulation at this period causes a normal auricular contrac- 

 tion with an appreciable * latency, and followed by a ventricular 

 contraction. 



Stimulation of the Auricle — Maximal. 



Maximal stimulation of the auricle almost always produces some 

 effect both on the ventricular and auricular beat : this effect is usually 

 •one of stimulation, but it may be of apparent inhibition. 



Fig. 6. 



b. 



Stimvilation of Auricle (maximal). 



