Electrode Jelly in Electrocardiography

In the early days of electrocardiography it was the recognized practice to place a patient's hands and left foot in three large saline pots. With the introduction of contact electrodes more than fifty years ago (James and Williams, 1910) and their later improvement by Cohn (1920), this ritual of partial immersion slowly gave way to swathing the limbs in bandages incorporating saline pads and malleable metal electrodes. Saline pads, however, brought new difficulties: bedclothes were liable to become moistened with saline in bedridden patients resulting in short-circuiting, and drying of the pads caused increasing skin resistance particularly during prolonged experimental observation. These disadvantages were overcome by Boas (1928) who dispensed with saline pads for the purpose of cardiotachometry. He found that two concave metal chest electrodes of one inch diameter filled with soft green soap as a contact material and tied to the chest by tapes gave consistently satisfactory tracings during three hours of continuous recording. Following this early demonstration that a simple contact medium, consisting of an almost neutral mixture of potassium oleate and glycerine, could give acceptable electrical recordings of the heart beat, it later became fashionable in electrocardiography to use an abrasive electrode jelly or paste rich in sodium chloride. Because of the inherent tendency for string galvanometer machines to "overshoot", Jenks and Graybiel (1935) devised a method for overcoming skin resistance and avoiding "overshoot" by concocting an electrode paste rich in sodium chloride and a pumice abrasive which effectively removed the superficial layers of the skin, thus greatly enhancing skin conductivity (Bell, Knox, and Small, 1939). Commercial electrode jellies and pastes consisting principally of sodium chloride and an abrasive soon became available, so that Russell (1935), using a string galvanometer machine, was able to recommend Cambridge electrode jelly for routine electrocardiography.