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Rh benign parasites rarely give rise to pernicious attacks, the malignant parasites frequently do.

The benign parasites are of two kinds: one, the quartan parasite, having a cycle of seventy-two hours, causing a fever recurring every three days—quartan fever; the other, the tertian parasite, with a cycle of forty-eight hours, causing a fever recurring every two days—tertian fever.

The malignant parasite has three forms, perhaps more: a pigmented parasite, the subtertian, of forty-eight, or approximately forty-eight hours' cycle; a pigmented parasite—pigmented quotidian—of approximately twenty-four hours' cycle; and an unpigmented parasite—unpigmented quotidian—also approximately of twenty-four hours' cycle.

We may arrange them thus:—

Clinical classification.—Formerly, classification being based entirely on clinical phenomena, malarial diseases were divided into quotidian,