A 100mm petri dish containing water is placed on an overhead projector. When solid Pb(NO 3) 2 is place on one side and solid KI on the other, PbI2 precipitates in the center.

There are small petri dishes, there are large petri dishes, and then there is MEGA, an enormous, 2-foot-by-4-foot slab of black agar infused with a gradient of antibacterial drugs. Researchers built ...