. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. 546 PHYSIOLOGY OF THE DOMESTIC Fig. 228.—Pulse Tracing op the Frog's Heart. (Sanderson.) pulsation of the heart the column of mercury sinks in one arm of the manometer, while it rises a corresponding distance in the other, carrying with it the piston, which by means of its pen traces a line composed of a succession of curves on the smoked surface of the revolving drum. The ascending limb of each curve corresponds to the systole of the
. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. 546 PHYSIOLOGY OF THE DOMESTIC Fig. 228.—Pulse Tracing op the Frog's Heart. (Sanderson.) pulsation of the heart the column of mercury sinks in one arm of the manometer, while it rises a corresponding distance in the other, carrying with it the piston, which by means of its pen traces a line composed of a succession of curves on the smoked surface of the revolving drum. The ascending limb of each curve corresponds to the systole of the ventricle, and the descending curve to its diastole (Fig. 228). By irritating the vagus with a weak induction current the heart stops in diastole, a result similar to that obtained in the previous experiment when the line of junction of the auricle and sinus venosus was irritated. This identical result, however, has not been produced by the same mechanism, as may be seen if to the serum in the reservoir a few drops of dilute solution of nico- tine be added; if the vagus now be irritated, no arrest of the heart occurs. The vagus has been paralyzed by nico- tine ; it no longer is able to restrain the heart, which beats faster than be- fore. (When the nicotine is first given the heart is slowed, and then quick- ened, the slowing being due to the first effects of the nicotine on the vagus, irritating it before it paralyzes it.) It would seem that nicotine and atropine have the same action. But it will be remembered that after atropine poisoning it is impossible to stop the heart through electric irritation of the sinus venosus. But if the sinus venosus be irritated in the heart which has received the nicotine, it will stop. Therefore, nicotine and atropine must act on different inhibitory organisms. If in a frog which has been placed under the influence of nicotine the heart be removed and placed on a watch-glass, it will pulsate regularly. If a drop of saline solution containin
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