colony counter

 an instrument designed to conveniently count or assist counting colonies{9} of microorganisms on a plate containing a gelled growth medium. One variety uses a pencil-like rod with a metal tip, which is connected by an electrical connection to the gelled growth medium; when touched to a colony{9} on the plate, the completion of the electrical circuit causes an increment of 1 unit on the readout of the colony counter.  [PJC]