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III] varieties of the malaria parasite besides those described by the Italians, and that the list here given will have to be enlarged or recast in the future. Men with extensive experience of malarial disease in their own persons tell us that they can discriminate by their sensations and symptoms between the fevers of different localities. Analogy would incline us to believe that clinical differences of this sort depend on differences in the determining parasites.

Before proceeding with a description of the various malaria parasites and their associated fevers, there are certain generalities which, to save repetition, had better be mentioned here.

Intermittent fever or ague.—— Every typical malarial fever is made up of a series of pyrexial attacks which recur at definite intervals of twenty-four, forty-eight, or seventy-two hours. Each attack consists of a stage of rigor, a stage of heat, and a stage of sweating; these are followed by a period, " the interval," of apyrexia -actual or relative. The duration and intensity of the constituent stages vary considerably. On the whole, they observe a certain proportion to each other; as a rule, the more pronounced the rigor, the higher the fever and the more profuse the sweating. Such attacks, with well-marked intervals of apyrexia, are designated intermittent fevers or agues. The expression " ague " is applied only to intermittents having a pronounced rigor stage.

Premonitory stage.—— Before rigor sets in, and sometimes for several days before the actual disease declares itself, there may or there may not be a premonitory stage marked by lassitude, a desire to stretch the limbs and to yawn, aching of the bones, headache, anorexia, perhaps vomiting, perhaps a feeling as of cold water trickling down the back. If the thermometer be used, it will be found that body temperature has begun to rise, it may be some two or three hours before the other and more striking symptoms which ensue set in; or it may be that the threatened attack will subside spontaneously without