Here is a second version of the gravitate particle system exploration in which the particles are rendered to look like microorganisms in a petri dish.

Quartz Particle Petri Dish from Noah King on Vimeo.

This is a Quartz Composer composition, exported to video using QuartzCrystal by Kineme.

A particle system, which is rendered to resemble bacteria, follows the mouse around using attraction/gravitate forces.