Particle Image Velocimetry Around Swimming Paramecia

Microorganisms like paramecia propel themselves by synchronously beating thousands of cilia that cover their bodies. Using micro-particle image velocimetry ($\mu $PIV), we quantitatively measured velocity fields created by the movement of \textit{Paramecium multimicronucleatum} through a thin ($\sim $100 $\mu $m) film of water. These velocity fields exhibited different features during different swimming maneuvers, which we qualitatively categorized as straight forward, turning, or backward motion. We present the velocity fields measured around organisms during each type of motion, as well as calculated path lines and fields of vorticity. For paramecia swimming along a straight path, we observed dipole-like flow structures that are characteristic of a prolate-spheroid translating axially in a quiescent fluid. Turning and backward-swimming organisms showed qualitatively different patterns of vortices around their bodies. Finally, we offer hypotheses about the roles of these different flow patterns in the organism's ability to maneuver.