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64 hours, resembles that caused by the quartan parasite (Chart 2).

Many authorities refuse to recognize more than one species of crescent-forming parasite. On the other hand, carefully conducted observations, both microscopical and clinical, seem to indicate a plurality of species. I shall follow the latter view.

The three parasites (Plate I, Fig. 3, and Plate II., Fig. 1) described by the Italian pathologists in connection with malignant malarial infection, although often associated together as well as with the benign parasites, are each of them occasionally found in what may be termed pure culture. From a study of such cases the morphological and distinguishing characters of the different species, and their special pathological effects, have been more or less satisfactorily made out. Although much remains to be done, enough is already known to enable us, in a measure, to differentiate them from each other as well as from the benign parasites, and to justify their being placed in a group by themselves. Characters possessed in common by the malignant parasites.—— One notable feature in regard to them is that they are very much smaller than the benign parasites. The earlier unpigmented phase, owing partly to minuteness, partly to its forming but a thin and very transparent object in the hæmoglobin, is hard to see. When first mounted on the slide the amœboid movements are very active (Plate I., Fig. 3, d). In a short time these subside somewhat, and then the little parasites tend to assume a more passive condition and to arrange themselves as tiny, though very definite and easily recognized, rather bright, colourless rings (Plate I., Fig. 3, a, b, c, e). Sometimes these rings may revert to the amœboid condition, and this, perhaps, for several times in succession; ultimately the ring form becomes permanent. Multiple infection of individual corpuscles (Plate I., Fig. 3, g) is often encountered, and this much more frequently than in the benign infections; doubtless, this is owing to the