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6 movement of the hæmozoin particles, the parasite is passive.

Structure of the parasite.—By appropriate staining of the free spherule (Fig. 2, b, c, d) it is found to consist of a minute, deeply tinted chromatin mass, the nucleolus, surrounded by an unstained area regarded by many as a vesicular nucleus, and this again by a somewhat lightly tinted covering of protoplasm. After the spherule has entered a blood corpuscle (Fig. 2, e), staining shows that the vesicular nucleus has become larger and more distinct, that the protoplasm has increased in bulk, and that the deeply stained nucleolus, which is sometimes double, has

Fig. 2. Evolution of the tertian parasite, stained (see text).

come to lie eccentrically in the nucleus, and both of them eccentrically in the protoplasm. On account of the relatively large size of the unstained nucleus, the eccentric position of the deeply stained nucleolus, and the narrow rim of stained protoplasm, the younger parasites look like so many minute blue signet-rings stuck on to the blood corpuscles. As the parasite grows and approaches maturity the nucleolus enlarges, becomes less defined, and then disperses; the vesicular nucleus also becomes enlarged and less distinct (Fig. 2, f, g, h, i). Finally, just before sporulation, both nucleus and nucleolus cease to be distinguishable (Fig. 2, j, a). At this stage these elements become fragmented and diffused throughout the protoplasm. Later the nuclear elements reappear as numerous minute, scattered nucleoli; and it is