GERD GUENTHER / SCIENCE PHOTO LIBRARY GERD GUENTHER / SCIENCE PHOTO LIBRARY
Microscope footage of Paramecium caudatum, a ciliate protozoa, showing the effect of an applied electric field on their movement. Normally the Paramecia swim about randomly. A voltage is then applied, as shown by the appearance of a positive and negative symbol. The Paramecia then show 'negative galvanotaxis', movement towards the negative terminal, the cathode (upper right). This forced locomotion of Paramecium in a DC electric field was first described by Max Verworn in 1888, but it was poorly understood. It was later found that the current changes the beating pattern of the cilia by overriding the electrochemical processes that the Paramecia use to control their motion. Hence it is not a beneficial evolved taxis like movement towards food or light, but a physical effect of the current on the organism. Filmed with darkfield illumination, frame width 1.5mm.
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