Cancer research. Researcher using a cell counter during research into cancer and toxins. Counting cells is called cytometry. This is a Z1 Series Coulter Counter. It uses the Coulter principle to count cells or particles in the 1-120 micron size range. The Coulter principle uses changes in the electrical resistance of the cells as they pass between two electrodes in an electrolyte solution. Photographed in the Health and Pollutants Laboratory of the INRS (the French National Institute of Research and Safety), Nancy, France. Tests are carried out here to establish the toxicity and cancer-causing properties of different materials, chemicals and pollutants.