COOLED HEART-STIMULATION OF AURICLK 601 



Instead of the gutta-percha support for the heart already 

 described, a hollow copper pan of similar shape was employed. 

 It was provided with influx and efflux tubes, and insulated 

 below by a plate of ivory in which ran also the electrodes 

 destined for the stimulation of the sinus. This was connected 

 with the usual support passing over the body. Upon minimal 

 stimulation of the ventricle itself the succession of auricular and 

 ventricular contraction is illustrated in the charts A 1 — 4 (Fig. 

 193) here inserted. It is seen that the action of cold modifies 

 considerably the relation between the ventricular contraction and 

 the succeeding auricular beat. In Ag we find a reduplicated 

 ventricular beat succeeded by a normal auricular contraction. 



In Ag cooled through about 2°'5 C, the ventricle responds to 

 the same stimulation, and the way does not pass upward to the 

 auricle ; and in A^, in which the contraction and relaxation of 

 the heart had become very slow from a further reduction of 2°, 

 we find the auricular rhythm is regular in spite of ventricular 

 reduplication. There is in A^ and A^ an indication of aortic 

 expansion ; it is to be noticed that after the reduplication in A^ 

 this is omitted. 



Auricular Stimulation. 



Many additional experiments upon cooled hearts have tended 

 to show that it is very rarely that stimulation of considerable 

 strength calls forth a ventricular beat, preceding or coexistent 

 with the auricular. Usually at all phases of stimulation which 

 cause a reduplication of the auricular beat, the ventricular succeeds 

 in normal relationship (B 1 and 2 Fig. 194). There is an excep- 

 tion to this, however, which is frequently demonstrated ; this is 

 that whilst the auricular beat is reduplicated the ventricular is 

 not, but is succeeded by a long diastolic pause (Bg), after which 

 the auricle takes up its old rhythm. Still more rarely stimulation 

 just before commencement of ventricular systole causes omission 

 of both succeeding auricular and ventricular beats (B^). 



The latency of reduplication varies considerably in minimal 

 stimulation of the auricle, but this variation is not so much 

 owing to loss of time in the auricular as in the ventricular 



