Production of Reversed Cardiac Mechanism in the Dog. 37 



cessation of the contractions of the whole heart," that "after 

 excision of the sinus node and the ensuing stoppage, the rate of 

 the whole heart falls and does not again reach the original rate," 

 and that "the function of the secondary pacemaker devolves on 

 no special portion of the heart." The results of experiments per- 

 formed by others and differing from ours were mentioned at that 

 time. I have continued the experiments on dogs, anesthetized 

 with ether, the hearts of which were left in situ and normally 

 nourished. After sufficient controls were registered electro- 

 cardiographically, the sinus node was clamped with a specially 

 constructed T clamp, 5 cm. long and 1 mm. wide. In the perfused 

 hearts the rate fell 10 to 70 beats, usually 30 to 50 beats, after the 

 node was excised. In the present series the fall in rate was 10 to 

 90, usually about 50. Stoppage, which is a usual phenomenon in 

 excised hearts, occurred also in these, but very rarely. The site 

 of the secondary pacemaker varied in these, as it did in the per- 

 fused hearts. Photographs of three hearts showing the areas of 

 the auricular surfaces which had been included in the jaws of the 

 clamp, and a series of curves from each of the corresponding experi- 

 ments and of one in addition were demonstrated. The relation of 

 the disturbed function of the heart to the area clamped will be 

 investigated histologically and reported in detail later. The 

 curves indicate that in each of these cases, there was a dislocation 

 of the pacemaking function from the site responsible for it, and 

 that, after clamping had taken place, this function devolved upon 

 the ventricles, the junctional tissues or another portion of the 

 auricle. In one of the experiments, first the ventricles (more 

 probably the junctional tissues) and later the auricles set the pace. 

 One of the experiments yielded curves which bore a close re- 

 semblance to those obtained from a patient by Williams and 

 James, 1 in which the wave representing auricular contraction was 

 found between the R and T waves, and was inverted. It is 

 demonstrated by the experiments that after clamping an area 

 along the sulcus terminalis, a site other than the normal pacemaker 

 assumes the pacemaking function and that a "reversal of the 

 cardiac mechanism" takes place. 



1 Proc. Soc. Exp. Biol, and Med., Oct. 16, 1912, X, 13. 



