1888.] 



Inhibition of the Mammalian Heart. 



211 



auricles to ventricles. At certain phases of vagus stimulation the 

 ventricles often fail to respond to auricular beats, while at the same 

 time there is evidence to show that this is due not to a depression of 

 the ventricular excitability, but to a break in the transmission of the 

 contraction from the auricles. 



7. The maximum intensity of the inhibitory influence exerted by 

 vagus stimulation often obtains at the same time in the auricles and 

 the ventricles. But frequently the auricles become greatly depressed, 

 while the ventricular beats are of undiminished size, or are only 

 beginning to be affected ; in rare cases the ventricular contraction 

 force becomes reduced more suddenly than the auricular. 



8. The effects of vagus stimulation on the ventricles may be in 

 some measure counteracted by the application to the ventricular surface 

 of a series of stimulations {e.g., single induction shocks) at about the 

 normal rate of the heart's action. An artificially excited series of 

 beats is thus caused ; these beats give curves of approximately normal 

 form and duration, and they are much stronger than any slowly occur- 

 ring spontaneous beats that appear after the standstill has lasted for 

 some time ; they are also much stronger than single beats excited (by 

 induction shocks) at long intervals daring the standstill. The beats of 

 the artificially excited series (at normal rate) are still decidedly 

 weaker than normal beats. 



On the Existence of a Local " Inhibitory Area " in the Heart. 



By stimulation of a certain locality on the dorsal aspect of the 

 auricular surface, certain striking effects are obtained. In the cat and 

 dog the area in question is elongated in shape, and is situated over 

 the inter- auricular septum, its long axis running parallel with the 

 plane of the septum. It extends downwards to within a short distance 

 of the coronary sinus. At the right side of the area lies the termina- 

 tion of the vena cava inferior. 



Many nerves course downwards through this region ; there are also 

 numerous nerve-cells and ganglia. These, however, are not confined 

 to the area in question, but occur in considerable number over the 

 dorsal aspect of the left ventricle, especially in its septal half. The 

 nerves appear to be derived to a considerable extent from the left 

 vagus. The majority of the fibres are non-medullated, but medullated 

 fibres are also present (cat). Ganglia occur in special abundance 

 near the auriculo- ventricular groove. 



Stimulation of this area with an interrupted current gives results 

 that stand out in sharp contrast to those obtained by stimulating 

 other parts of the auricular wall, e.g., the appendix. Stimulation of 

 the latter causes an acceleration of both auricles and ventricles. The 

 auricles contract with great rapidity, so that they present a peculiar 



VOL. XL1V. Q 



