SUMMARY: The movement of the enormously enlarged filaments of grown on penicillin agar ceased, or was slowed down, by screening the culture from the radiant heat of a microscope lamp. Organisms stimulated by heat after resting a short time in this way moved more rapidly than before. The increased activity was maintained for longer periods with longer rests, the increment in the period of activity increasing gradually as the resting period increased. In the condition of the test, rests of 60–120 sec. produced a maximal response.

Repeated heat stimulation rapidly exhausts the capacity of the organisms to maintain a steady rate of movement. Under constant stimulation organisms maintain a fairly constant rate for some hours and then slow considerably as though they or their Hagella were exhausted. A small decrease in radiant heat energy can induce a reversal in the direction of movement.

Active flagella attached to immobile organisms react to heat stimuli in the same way.


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  1. Fleming A., Voureka A., Kramer I.R.H., Hughes W.H. 1950 J. gen. Microbiol 4:257
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