Effects of Viscosity on the Gravi-kinesis Responses of Swimming {\it Paramecia} Studied Using Manetic Force Buoyancy Variation

Previous studies have shown that {\it paramecia} exhibit negative gravi-kinesis. They exert a stronger propulsive force when swimming up than when swimming down. This behavior is very surprising since it suggests they sense their tiny apparent weight of only $\sim$ 80pN. In an effort to understand the mechanism of this sensing, we are testing how the viscosity of the swimming medium influences their gravi-kinetic response. We employ the technique of magnetic force buoyancy variation to simulate different effective gravity levels on swimming {\it Paramecia}. We are analyzing their swimming response employing a phenomenological model that relates the parameters describing their helical trajectories to the beating of their cilia.\\ This work was supported by NSF PHY0750360 and at the NHMFL by NSF DMR-0084173