Comet images of the lymphocyte cells stained with Ethidium bromide and observed under a fluorescent microscope. The photos a-f belong to the A-F group, respectively. Group A: negative control group with 2 mL of distilled water gavage, Group B: 30 mg/kg b.w of PQ by gavage, once daily for three days, Group C: 60 mg/kg b.w of PQ by gavage, once daily for three days, Group D: 200 mg/kg b.w of PQ once by gavage, Group E: 50 mg/kg b.w of PQ for three weeks, twice a week by gavage (total 6 times), F: 200 mg/kg b.w of ethyl methanesulfonate by gavage 24 and 3 h before blood sampling (positive control).