Clinical electrocardiography . Fig. 5.—Cambridge model electrocardiograph: A, Camera mechanism; C,lantern; D, electromagnets, microscopes, and fiber case; E, power control board;K, time marker; L, water-cooled condenser. that electric currents are produced with each beat of the introduction of the string galvanometer by Ader, in 1897,opened the portals to electrocardiography. The galvanometer is based on the physical law that a currentproduces a magnetic field which acts at right angles to its course, varies with the intensity of the current, and attracts or repels 26 ELECTROCARDIOGR
Clinical electrocardiography . Fig. 5.—Cambridge model electrocardiograph: A, Camera mechanism; C,lantern; D, electromagnets, microscopes, and fiber case; E, power control board;K, time marker; L, water-cooled condenser. that electric currents are produced with each beat of the introduction of the string galvanometer by Ader, in 1897,opened the portals to electrocardiography. The galvanometer is based on the physical law that a currentproduces a magnetic field which acts at right angles to its course, varies with the intensity of the current, and attracts or repels 26 ELECTROCARDIOGRAPHY 27 proportionately another neighboring magnetic field. The electro-cardiograph is but a modern elaboration of the original stringgalvanometer (Figs. 5, 6). The fiber of the electrocardiograph is a delicate quartz fila-ment from to mm. thick, it is barely perceptible tothe naked eye, and is coated with gold or silver to permit con-. Fig. 6.—Hindle model electrocardiograph: B, Batteries; C, control board; F,fiber house; L, lantern; M, electromagnet; P, camera. ductivity. It is suspended between the poles of a powerful electro-magnet (Fig. 7). The movements of the fiber, activated by cardiacaction, are recorded by projecting its shadow, magnified by ahigh-power microscope, on a camera mechanism. The time isrecorded by the shadow of a rotating spoked wheel activated by atuning-fork. 28 CLINICAL ELECTROCARDIOGRAPHY The current is obtained by applying electrodes to both fore-arms and to the calf of the left leg. Electrodes are made of zincor copper plated with silver. Several varieties are in use (,9); the shallow pans used in the Mayo Clinic are very convenientfor routine clinical work with ambulatory patients. Cohn hasrecently described a new electrode, simple in construction, con-sisting of a strip of lead foil cm. wide and 22 cm. long, and a ~umrnr\
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