Thermally-induced Explosive Migration of Paramecium

Summary: In the course of developing methods to obtain dense populations of the ciliated protozoon Paramecium aurelia with undisturbed physiology and free from growth medium, attempts were made to elicit a positive phototactic response. No phototaxis was observed, but a dramatic positive thermotaxis was demonstrated. When a dilute buffer was layered over the more dense culture fluid and a thermal gradient induced, the ciliates first collected at the buffer/culture fluid interface and then moved explosively through it to the top of the buffer layer. Concentrations of 105 organisms/ml. were obtained.