Interaction of two swimming Paramecia.

The interaction between two swimming Paramecium caudatum was investigated experimentally. Cell motion was restricted between flat plates, and avoiding and escape reactions were observed, as well as hydrodynamic interactions. The results showed that changes in direction between two swimming cells were induced mainly by hydrodynamic forces and that the biological reaction was a minor factor. Numerical simulations were also performed using a boundary element method. P. caudatum was modelled as a rigid spheroid with surface tangential velocity measured by a particle image velocimetry (PIV) technique. Hydrodynamic interactions observed in the experiment agreed well with the numerical simulations, so we can conclude that the present cell model is appropriate for describing the motion of P. caudatum.