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THE different clinical types of malarial disease are associated with different and corresponding species of malaria parasites.

Classification of parasites.—— The different species have been classified according to
 * 1. The duration of their respective life-cycles inside the human body.
 * 2. Their morphological characters.
 * 3. The clinical phenomena they give rise to.
 * 4. The results of inoculation experiments.

It may be said that, so far as these tests go, there is evidence of plurality of species. That is to say, a particular clinical type of malarial disease is associated with a parasite of definite morphological form and intracorporeal life-cycle, characters which are maintained when the parasite has been inoculated experimentally.

The classification suggested by Mannaberg will here be followed a classification based principally on the investigations of Golgi, Marchiafava, Bignami, Celli, Grassi, and other Italians, as well as on his own most excellent work. The forms of the malaria parasite, and of the diseases they give rise to, may be divided into two comprehensive groups—— the benign and the malignant. A principal morphological distinction between these two groups is that, whereas the benign parasites never form crescent bodies, the malignant parasites, or at least the most important of them—— the subtertian——form crescents; that is to say, the gamete of the benign parasites is a sphere or disc, that of the malignant parasites a crescent. A principal clinical difference between the two is that, whereas the