Effect of extracellular material from plates containing swarming cells on swarming. Light microscopy of P. vortex moving on MH agar (0.3% w/v), extending into an area where extracellular material derived from washes of swarming cells was delivered by toothpick and allowed to soak into the agar. Time of frame capture is noted in seconds. Second 0: Area of extract outlined in blue dots with direction of cell mass elongation shown by the black arrow. Dark marks inside the area of the extract are disturbances due to the toothpick contacting the agar. Second 30: cell mass starts to disperse as it contacts the area of the extract. Second 44: Cell mass has dispersed into area of extract. Second 60: Additional cells are moving into this area from further back in the colony; the cell mass is growing in volume at the tip and extends in the direction of the red arrow.