Medical electronics has its origins in basic physiological research, a field in which there has been a continual searching since the early years of the last century for instruments capable of detecting and measuring the electric currents which accompany the activity of nerve and muscle fibres (Fig. 1). The discovery of the magnetic effects of a current by Oersted in 1819 was followed by the invention of the tangent galvanometer by Schweigger in 1820, and the moving coil galvanometer by Sturgeon in 1836. Both types of instrument were used by physiologists but they were insensitive and slow in response. Bernstein's work, published in 1871, was a classic example of the victory of ingenuity over the limitations of a sluggish measuring instrument. He employed what we should now call a ballistic galvanometer in series with electrodes attached to a frog's muscle and a special switch. This switch applied a momentary electrical stimulus to the muscle, and then closed the circuit to the galvanometer after a predetermined time interval. By varying this time interval and repeating the stimulus, Bernstein laboriously built up a graph of the current against time. His curve was sur‐prisingly similar to those obtained today using electronic recording techniques (Fig. 1b). The duration of the action current, as it was called, was a few milli‐seconds. Bernstein was able to show further that the action current was pro‐pagated along the muscle fibres with a velocity of the order of 1 metre per second.
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