Because of its simplicity and ease of operation, and because it has certain technical advantages, I wish to describe an electrode for use when taking electrocardiograms of ambulatory patients. Electrodes consisting of a metal plate bound to the extremity by bandages wet with hot salt solution are commonly used for bed patients, 1 but for ambulatory patients the zinc—zinc sulphate—salt solution type of nonpolarizable electrodes are recommended. 2 These latter are a quite unnecessary complication of the technic. The simple electrode to be described will take technically perfect records. It consists of a glass tank for each extremity, that for the arms being a cylinder about 7 × 10 inches and that for the leg being rectangular, about 7 ×7 × 12 inches (a fish aquarium). In these are stood metal plates 4 inches wide and extending up above the top of the tank, to which plates the wires from the galvanometer