. An introductionto physiology. aline solution, rest onthe beating heart, one on the base, the other onthe apex. These electrodes will follow the move-ments of the heart. Connect the electrodesthrough a short-circuiting key to the electrom-eter. During the diastole, the meniscus will remainat rest. At each beat of the ventricle, themeniscus will move; first in a direction indicatingthat the base is negative to the apex, and thenin the opposite direction. The action currentpasses over the heart from base to apex. These experimei*ts show not only that thereis an action current at each systole of
. An introductionto physiology. aline solution, rest onthe beating heart, one on the base, the other onthe apex. These electrodes will follow the move-ments of the heart. Connect the electrodesthrough a short-circuiting key to the electrom-eter. During the diastole, the meniscus will remainat rest. At each beat of the ventricle, themeniscus will move; first in a direction indicatingthat the base is negative to the apex, and thenin the opposite direction. The action currentpasses over the heart from base to apex. These experimei*ts show not only that thereis an action current at each systole of the heart. 174 THE PHYSIOLOGY OF MUSCLE AND NEEVE but are evidence also that the resting heartmuscle is iso-electric {i. e. of uniform potential).The Action Current precedes the Contraction. —Eemove the heart, including a portion of thegreat veins. Set the metal heart-holder (Fig. 42)on the base of the iron stand and place the heart,together with some normal saline solution, in thespoon of the holder. Eest the upright of the. Fig. 42. The heart-holder. straw heart-lever on the ventricle (the levershould be counterpoised with a washer orother weight). Make a nerve-muscle the femur in the upper side of the muscleclamp, at right angles to the long axis of theclamp. Bring the latter near the heart-holder, sothat the nerve may rest on the ventricle. Fas-ten the tendon Achilles to the muscle lever bya thread which passes over the pulley on the THE ELECTROMOTIVE PHENOMENA 175 axis of the lever before being secured to thelever. Thus the muscle, though below the lever,will pull it upwards when contraction takes the two writing points be in the same ver-tical line. Start the drum at rapid speed. Twocurves will be recorded: one by the contractionof the ventricle, the other by the rheoscopic mus-cle, stimulated to contract by the action contraction of the rheoscopic muscle willslightly precede the contraction of the ventricle. Current of Action o
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