On the Effect of Vagus Stimulation upon the Conductivity of Tortoise Heart.

It was found, from the curves of mechanical registration that the precise determination of atrio-ventricular interval and the time interval from the beginning to the summit of ventricular contractions cannot be accurately measured. But it was clearly shown that the height of auricular contractions is obviously reduced by vagus stimulation as well as by the application of acethylcholin, which is generally known as "Vagusstoff" while on the other hand the ventricular contractions are not affected. It is considered, therefore, from the results obtained, that the acethylcholin like substance is produced from the endings of vagus nerve as a conseqence of its activity through stimulation, and that this substance causes a decrease in the height of auricular contractions. Examining the electrocardiogramm, it clearly showed a marked prolongation of the atrio-ventricular interval, and in the last three curves it failed to record the ventricular contraction after each P-spike. Hence it is considered that vagus stimulation affects the conductivity of atrio-ventricular bundle and causes diminution of its conductivity. The results above cited, agree with those of the former investigators. But with regard to the duration of the electrical response of the ventricle, it was found contrary for the vagus stimulation has no effect upon the function of ventricular muscle. From the results obtained, the following conclusions may be made. 1. The vagus stimulation affects the negative inotropic only on auricular contraction. 2. The vagus stimulation affects the negative dromotropic on the conductivity of atrio-ventricular bundle. 3. The vagus stimulation has no effect upon the function of ventricular muscle.