. Electronic apparatus for biological research . Figure in peering down a dissecting microscope at the site of the recording electrode tip, auditory information about what is being recorded may be extremely welcome. A straightforward audio-frequency amplifier and loudspeaker enable one to hear action potentials, and in addition there is a sudden change in noise level at the instant when the microelectrode tip, which is usually invisible, first makes contact with the tissue. This reduction signals the point at which to zero the micromanipulator dial gauges so that hence- forward they are
. Electronic apparatus for biological research . Figure in peering down a dissecting microscope at the site of the recording electrode tip, auditory information about what is being recorded may be extremely welcome. A straightforward audio-frequency amplifier and loudspeaker enable one to hear action potentials, and in addition there is a sudden change in noise level at the instant when the microelectrode tip, which is usually invisible, first makes contact with the tissue. This reduction signals the point at which to zero the micromanipulator dial gauges so that hence- forward they are direct reading in penetration. A simple loudspeaker amplifier and power pack are shown in Figure This is another unit recommended for beginners, and in conjunction with the single-sided pre-amplifier. Figure , enables a start to be made in electrophysiological work. The bleater Useful as the above amplifier is, it cannot signal the magnitude or polarity of a steady potential at a microelectrode tip; on piercing a muscle or nerve cell membrane the loudspeaker would merely emit a 'plop'. A device which does, which is not really an amplifier at all but which it seemed appropriate to mention here, is the 'bleater', first reported by Draper and Weidmann^^. A possible circuit is shown in Figure A thyratron relaxation oscillator has its frequency controlled by a bias derived in part from a battery and 636
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