Anodal Contraction of Paramecium Protoplasm*

SYNOPSIS. Paramecia immobilized on an agar surface were stimulated with pulses of 2–8 mamps/cm2 with intervals ranging from 1.0 to 1000 msec. High speed cine films (1500‐6000 frames per second) of the animals' responses were analyzed to determine changes in body length and the effects on cilia and trichocysts. At current densities in the range of 1.0 mamp/cm2, rapid ciliary reversal occurred. Above this value the paramecia shortened. This body contraction can be very rapid, resulting in shortening to 95% of the body length in 0.95 msec. At all levels of stimulation, contraction of the body length occurred 1st anodally, then cathodally. Extensive trichocyst extrusion occurred 1st at the anode and later at the cathode at current densities greater than 5 mamp/cm2 in the agar. Results of this study indicate that the protoplasm of paramecia is capable of very fast contraction in response to electric stimulation and that the initial response is always anodal.