The tumultuous auricular activity which follows faradization of the auricles of mammals and which has been variously described, could be distinctly seen to consist almost constantly in our experiments on dogs of true fibrillatory movements of the separate muscle fibers coëxisting with a rapid auricular tachycardia. During peripheral stimulation of the right vagus nerve the true fibrillation alone existed, the tachycardia being inhibited.

A comparison of the electrocardiograms from dogs with this abnormal auricular activity with those from patients with the type of cardiac arhythmia which has been attributed to auricular fibrillation, and from patients with so called auricular flutter, indicates that the auricular activity in patients with either of these conditions differs somewhat from that usually seen in the faradized auricles of the dog in our experiments. The auricular activity of the cases of cardiac arhythmia is apparently true fibrillation, similar to that seen in the faradized auricles of the dog during right vagus stimulation.

The electrocardiograms from cases of so called auricular flutter usually give no evidence of auricular fibrillation, and the auricular activity seems to consist of tachycardia alone. Fibrillation may apparently coëxist with the tachycardia in some cases, when the auricular activity seems to resemble closely that usually seen in the dog after auricular faradization. During peripheral stimulation of the left vagus nerve, the electrocardiograms obtained after auricular faradization show changes which render them more nearly similar to those obtained from patients with auricular flutter. The facts that the auricular activity of the faradized auricles of the dog may apparently pass spontaneously into that closely resembling auricular flutter in man, that it may be changed into true fibrillation by right vagus stimulation, and that the abnormal auricular activity in man passes from a state of flutter to that of fibrillation in a similar manner, may be taken as evidence for the belief that auricular fibrillation and auricular flutter in man are closely allied cardiac disorders.

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