Abstract
The effects obtained in the action of dogs'hearts on stimulating the peripheral stumps of both vagus nerves were studied in fifty-four experiments. The dogs were anesthetized with ether without adjuvant, artificial respiration was maintained by the Meltzer-Auer method, and registration was accomplished by the galvanometric method. When the chest was opened, curves of auricular and ventricular contractions were also inscribed. Faradic stimulation was employed. The secondary coil of an inductorium, fed by a 2-volt dry cell, placed arbitrarily at 50 mm., was the source of the current.
On stimulating the right vagus nerve, the usual effect was obtained; both auricles and ventricles ceased to beat, generally throughout the period of stimulation. Occasionally the ventricles escaped from inhibition, but then the impulse to contraction arose and spread in an abnormal manner; the structures normally concerned with these functions remained inhibited.
When the left vagus nerve was stimulated in the same dog, with a current of the same strength, a difference from the effect of stimulating the right nerve was observed in 88 per cent. of the fifty-four experiments. The auricles did not cease to beat, they were merely slowed,—sometimes 100 or more beats. In one group, normal ventricular contractions ceased entirely in twenty-four cases. In a second of twenty-four other cases, a ventricular contraction followed every second, occasionally every third, fourth or more auricular beats, the mechanism being one of incomplete dissociation. In a third group, the only effect of stimulation was an increase in the time occupied in conduction from auricles to ventricles.
In the first group when the left vagus was stimulated, as has been stated, normal ventricular activity ceased, but abnormal activity occasionally continued. The rate of the abnormal ventricular contractions differed from that of the slowed auricles and complete As-Vs dissociation resulted.
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