Retrospectroscope-contributions of the vacuum tube to early electrophysiological research

Modern-day bioelectric recorders such as the ECG and EEG are common, providing useful clinical information. However, their present-day perfection had to await the generation of knowledge about fundamental bioelectric events, which required the creation of sensitive and rapidly responding potential recorders. Despite the initial lack of such devices, a considerable amount of electrophysiological knowledge was acquired with quite primitive instruments. However, addition of the vacuum tube amplifier to these early instruments and to the Braun (cathode-ray) tube provided the first clinical electrographic instruments. This article recounts some of this early background and traces the evolution of the amplifier from the Edison lamp to the Fleming valve (diode) to the DeForest Audion (triode) and to the first amplifiers used for electrocardiography and electroencephalography.