ANALYSIS OF MOTILE TRACKS OF PARAMECIUM UNDER GRAVITY-FIELD

Two-dimensional swimming tracks of paramecia on the vertical plane wer e photographed by 4-sec exposure under a dark field. The orientation r ate (meaning the degree of upward curvature of the swimming path) was measured under various experimental conditions. The rate decreased in a K-rich medium as well as in a viscous methylcellulose solution. The decreasing tendency of the orientation rate was closely coupled with t hat of swimming velocity. The rate was also decreased in a solution wi th a high specific gravity which was made up by heavy water, The speci men did not show geotactic orientation either during or just after the application of an electric current. The motile behavior of the indivi dual specimen under gravity, which was recorded on videotape, showed t hat a larger angular change in the cell axis was always coupled with a n upswing phase of the gyration. The theoretical equations of motion f or physical models were set up, and the most probable mechanism was di scussed on the basis of the present findings.