抄録
Many ciliates swim upwards against sedimentation by gravity. The negative gravitaxis of Paramecium disappears in solutions of about the same specific gravity (sp.gr.) of the cells (1.04). The gravitaxis becomes positive in solutions of higher sp.gr. (l.08). This result indicates that the gravitaxis is related to the movement of the cells relative to the medium. The results of parabolic flight experiments and those of free fall experiments indicate that the gravitactic behaviour is the topotaxis of the organisms. Free-fall experiment using solutions of various sp. gr. is a useful method for investigating the gravitactic responses. Effects of reduced gravity have been observed by using a drop tower, which provides a transitional phase of low gravity before starting the free fall. Some changes in parameters of the helical tracks, such as an increase in wavelength, were observed after the start of the low gravity phase.
