Clinical electrocardiography . 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
Clinical electrocardiography . 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\. Stav,dardizj>,<j , Fig. —Essential wiring of the electrocardiograph: M, Electromagnets;L, lantern; C, camera; T, time marker; LL, left leg; LA, left arm; RA, rightarm; F, fiber; MS, microscope. strip of rubber sheet 9 cm. wide and 30 cm. long. The stripsare fastened together near one end by a brass screw, which alsocarries the binding-post. The electrolyte is a 20 per cent, saline solution used as warmas can comfortably be tolerated by the patient. The current represents not only the cardiac action currentsbut also the difference of potential between the parts of the bodyto which the electrodes are applied; application of the electrodes ELECTROCARDIOGRAPHY 29 is dependent on local conditions of the skin and tissues. On thisaccount it is important to have the skin of the contact areas thor-
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