1888.] 



On the Rhythm of the Mammalian Heart. 



207 



impulses reaching them from the terminal or " ostial " parts of the 

 great veins. For though both auricles and ventricles possess an 

 inherent rhythmic tendency, the ostial parts of the great veins possess 

 a higher power of spontaneous rhythm, and hence dominate the 

 rhythm of the whole heart. The rapidly recurring contractions 

 arising in the ostial regions are propagated over the whole organ ; the 

 more rapid rhythm of the .ostial parts supersedes and renders latent 

 the less rapid inherent rhythm of the auricles and ventricles. In 

 support <af this view there can be adduced many facts. Among 

 others — 



(1.) The independent rhythm of the auricles and ventricles appears 

 to be decidedly slower than that of the terminal or ostial parts of the 

 veins. 



(2.) Slight heating of the ostial part of a great vein (e.g., the 

 termination of the vena cava superior) causes a marked acceleration 

 in the rhythm of the whole heart, while a similar heating of the 

 ventricular wall causes very little change, or (more commonly) none 

 at all. 



Weak faradic and galvanic currents induce similar results in this 

 respect. 



(3.) In the dying heart the power of spontaneous rhythmic con- 

 traction survives longest in the ostial parts of the veins. This is 

 analogous to what obtains in the hearts of cold-blooded animals, where 

 the greatest vitality is exhibited by the sinus venosus, the part pos- 

 sessed of the highest spontaneous rhythm, i.e., the leading or dominant 

 part of the organ. 



5. The normal sequence of the ventricular contraction upon the 

 auricular contraction in the intact heart is essentially determined by 

 nervous influences. It is not dependent on — 



(1.) The distension of the ventricles with blood pumped in from 

 the auricles. 



(2.) The mechanical relations normally obtaining between the 

 auricles and ventricles through the medium of the auriculo- ventricular 

 valves and the chordae tendineas ; or 



(3.) The occurrence of an electrical change (current of action) in 

 the auricular muscle as one of the phenomena of its contraction. 



6. The nervous influence determining the ventricular sequence is 

 probably of an intermittent character. 



7. The propagation of the contraction within the walls of the 

 auricles and. ventricles is not dependent on the action of the nerves 

 lying near the surface of these parts. 



The contraction continues to be propagated quite well when the 

 surface (e.g., of the ventricles) has been washed with strong 

 ammonia. 



8. In the auricles at least, the ordinary beat is not the result of a 



