Cancer research. Light micrograph of two cell cultures in a petri dish. A normal cell culture is at left. A precancerous (neoplastic) cell culture (right) was caused by exposure to a cancer-causing chemical. This tests the chemical and studies its effects on cell cultures. 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.