It was found that with mixed malaria infections in the same experimental animal sulfanilamide eradicates a virulent P. knowlesi infection, leaving the animal with a milder chronic P. inui infection. Determinations of the metabolic activity of the two parasites in vitro showed that P. knowlesi consumed approximately six times more oxygen than P. inui. The addition of sulfanilamide in concentrations less than that necessary to effect a cure almost completely inhibited the respiration of P. knowlesi parasites in vitro, while the same concentrations of the drug against the same number of P. inui parasites had no apparent effect.

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