A Petroff- Hauser Counting Chamber Is

A Petroff- Hauser counting chamber is

A) a glass slide containing an etched grid for counting microbes directly using a microscope.
B) a device used to count numbers of bacterial colonies on a Petri plate.
C) a device that counts cells as they interrupt an electrical current.
D) an apparatus that traps bacterial cells on a membrane filter where they can be counted.
E) a device that measures the amount of light that passes through a culture.