488 



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



maximal maintenance of systole. In 3', after the injection of a small 

 dose of strychnia into the dorsal lymph sac, distinct spasm was 

 present, and in 5' fig. P x was taken, which showed that the refractory 

 period had become prolonged, until relaxation of the ventricle had 

 commenced. 



Time-marl er recording seconds. All tracings in Appendix C taken at this speed,. 



except S and T. 



It may happen that stronger stimulation before the maximum 

 of systole is reached, causes an auricular beat, which precedes 

 in normal rhythm the induced ventricular contraction. This is 

 observed when the electrodes are placed near the base of the ventricle, 

 or when stimulation is passed through the same portion of the heart 

 from the float to an electrode placed beneath the heart upon the- 

 supportiug shelf. After the maximum of systole, however, the 

 auricular contraction succeeds the induced ventricular. Both these 

 facts are demonstrated in fig. Q, in which this occasional increased 

 auricular excitability is shown. 



Auricular Stimulation . 



Occasionally maximal stimulation applied to the auricle produces at 

 all times an auricular contraction succeeded by a ventricular ; more 

 usually, however, this relationship exists only up to the maximum of 

 systole (ventricular), and thereafter the induced auricular beat 

 succeeds the ventricular. 



Should stimulation cause an instantaneous auricular systole, then 

 the ventricular reduplication has a latency of nearly equal value at all 

 times at which it may occur, but should there be, as in fig. B^ a 

 considerable auricular latency (about 1") then the ventricular latency 

 is liable to great variations. 



At the maximum of auricular systole, fig. Bo, we have an imme- 

 diate auricular response, and a ventricular latency of and in 

 fig. B (3) there is an almost instantaneous ventricular systole, with an 

 auricular latency of about 15". The diastolic pause is the longer the 

 later stimulation falls. In fig. B^ it is "9" ; in fig. B 2 it is l"^ ; in 

 fig. B 3 it is 2"'3. 



Stimulation falling just after maximum of auricular systole, and at 

 the commencement of ventricular systole, may cause in addition to the 

 results enumerated, omission of the succeeding auricular and ventri- 

 cular contractions, or reduplication of the auricular, but omission of 

 the succeeding ventricular (fig. S). 



