On the Action of Muscarin upon the Heart, and on the Electrical Changes in the non‐beating Cardiac Muscle brought about by Stimulation of the Inhibitory and Augmentor Nerves

IN Ludwig's Festschrift' I have described how an electrical variation of a distinct character accompanies the action of the inhibitory nerve of the heart of the tortoise when the auricle is quiescent. For the sake of the readers of the Journal of Physiology I reproduce (Pl. XII.) the plate which accompanied my paper and will briefly describe the nature of the experiment and the meaning of the curves figured there. The whole object of that investigation was to find out whether any electrical change could be demonstrated in the muscular tissue of the auricle of the tortoise as the effect of the stimulation of the vagus nerve when that auricle was not beating. The possibility of such an experiment was afforded by the presence of the coronary nerve, for I knew from previous experience' that, when the auricle was cut away from the sinus and the coronary nerve left intact (as depicted in Fig. 1, P1. XII.), the isolated auricle-and-ventriclepreparation would after a timne beat with its own rhythm and then stimulation of the right vagus nerve in the neck would diminish the size of the beats of the auricle; I knew also that after the separation from the sinus a variable length of time elapses during which the auricle and ventricle remaini quiescent, and during this period of quiescence stimulation of the vagus produces no visible effect. It was self-evident that the vagus must be active during this period of quiescence, for the result of its activity was clear enough in the shape of diminution of the contractions as soon as the auricle began to beat; and the nonmanifestation of that activity was clearly due simply to the want of suitable means of making it visible. Of the various means at