Abstract
During measurements of the circadian (approximately 24-hr) rhythms of spontaneous bioluminescence in the marine dinoflagellate Gonyaulax polyedra, the individual cultures in vials were shielded from otherwise constant dim light for 1-3 min every 20-60 min by a photomultiplier housing that was moved from vial to vial. The high-frequency dark pulses caused a small but consistent shortening of the free-running circadian period, but there was no indication that the dark pulses caused entrainment. Hardware and software components of the microcomputer-controlled data collection system are described. A microcomputer controlled the movement of the photomultiplier and acquired the data via an analog-to-digital converter. The algorithms distinguished and separately recorded background glow, intermittent flashes, and total light from populations ranging in number from 103 to 105 cells in volumes from 1 to 10 ml. Fast video display techniques allowed continuous on-line viewing of incoming data, together with a display of the data recorded over the preceding day or two. Detection of mechanical and software errors coupled with recovery systems maintained high reliability of data collection.