The vermicule, at first clubbed at one end, gradually elongates, and the nucleus becomes centrally placed, while the pigment is irregularly distributed. The forward movement is caused by a secretion of a "gelatinous " substance from the surface, as has been observed by Schaudinn. First and second days: The young zygotes are round rather than oval, and are distinguishable by their characteristic pigment as those of the simple tertian parasite, although, as a rule, non motile. They are also more transparent than those of the malignant tertian. In stained specimens several masses of chromatin appear. The size of the zygote about this date is 10 to 14 micro. Third day: The cyst wall is clearly defined, but is less thick than in the case of proteosoma cysts; the size has increased to about 12 to 16 micro, and the chromatin masses have progressively increased. The protoplasm is vesicular or reticulated. Fourth and fifth days: The cysts are visible with low powers as projections on the outer surface of the midgut, and, as in other cases, are most numerous at the posterior end of the gut nearest the origin of the Malpighian tubes. Sixth and seventh days: Signs of striation due to the formation of sporozoites are clearly visible, and in stained specimens these and the residual segmentation masses can be distinguished. It should be noted that even if the anopheline has been fed only once, the parasites are not all at the same stage of development at the same time, and, according to Bignami and Bastianelli, sporozoites may be fully developed in four days, though it takes on an average 8 to 10 days for the sporozoites to reach the glands. Brown spores have not been found by the Italians in cases fed on simple tertian parasites. If this observation is confirmed, it is evidently an important one, but probably an insufficient number of cases have been examined.
It is much more difficult to infect a mosquito with the quartan parasite than with the other species-at least, if we employ for this purpose a hospital case showing a typical quartan temperature chart, for in these cases flagellating bodies are found with difficulty and are few in number; but positive results have been obtained by the Italians and also by Christophers and myself in India, when, out of 19 mosquitos used, we got in 2 cases positive results. That this difficulty occurs in nature we cannot believe, because in some districts of India the quartan parasite was the only one found by us in the native children, and Anophelince caught in the native huts were constantly infected.
With regard to the sporozoites derived from the various parasites, it is difficult, if not impossible, to distinguish one from another. The developmental cycle requires, in the case of the malignant tertian parasite, an optimum temperature of about 27°, and ceases at lower temperatures of 15.5°-17.5° C In the case of the simple tertian, however, provided initially a suitable temperature has been maintained, development will still go on at temperatures as low as
12° or 9° C, but the appearance of sporozoites is then delayed for twenty one days. Further, the lowest temperature at which the simple tertian parasite will develop is 20°-22° C, and, in the case of the quartan parasite, 16.5° C. (Grassi).