We present the results of new experiments on the chlorite-iodide reaction and use these results to determine the roles of various chemical species in the reaction mechanism. We simultaneously monitor three species, I-, ClO2-, and I-2, and determine the relative phases of oscillations in these species. We use perturbations in these species and the additional species NaOCl, IO3-, Cl-, HIO2, and H2OI+ to perform qualitative pulsed-species response, concentration shift regulation, and concentration shift destabilization experiments. Within a scheme of categorization of oscillatory reaction mechanisms, we determine that the chlorite-iodide system is a category 1CX or 1CW oscillator. Further, we distinguish essential and nonessential species and identify ClO2- as a type Z essential species, I- as a type Y essential species, and HOCl as an essential species of type X or W. HOI and HIO2 are essential species whose roles we were unable to identify from these measurements I-2 and IO3- are identified as nonessential species of type B, while Cl- is a nonessential species of type C. Our assignments of the mechanistic roles of the essential species show complete agreement with those predicted by the Citri-Epstein mechanism. However, that model mechanism predicts that I-2 is a nonessential species of type C and that Cl- is a nonessential species of type B.