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Apparatus for detecting rate and direction of rotation of tethered bacterial cells.

A simple apparatus was constructed for detecting the rate and the direction of rotation of tethered bacterial cells. Images of the tethered cells from a dark‐field optical microscope were recorded by a TV camera and VTR. The playback image of a rotating cell was passed through an optical system consisting of an image splitter and two graded filters and then transformed into two electrically sinusoidal signals having a phase difference of 90°. Rotation rate of the cell image was determined from the frequency of the signal and the direction of rotation was detected from the phase shift between two signals. The range of the rate of rotation measurable was from 1.3 to 17 rps in the steady state and the change of the rate of rotation could be followed within 1 sec. For the detection of the direction of rotation the rate had to be less than 15 rps. The change of the direction of rotation could be detected within one or two cycles of the bacterial rotation.