Microscopical examinations in malignant fevers.—In malignant infections the pigmented phase of the fever-causing forms of the parasite is not very frequently met with in peripheral blood. When found, and especially when it is observed that the pigment has become concentrated, it is a sure indication that a paroxysm is impending. On the occurrence of chilliness or of rigor, and at least during the earlier stages of the paroxysm, many small unpigmented parasites, sometimes exhibiting active amœboid movement, sometimes appearing as rings, will be found in finger blood; but towards the end of the fever these unpigmented forms often diminish in number, and all evidence of parasitic infection may even disappear from the blood till the approach or incidence of the next paroxysm. Of course, crescents and pigmented leucocytes may be found during these temporary absences of the intracorpuscular parasites. The segmenting forms of the malignant parasite are best found by aspirating the spleen with a hypodermic needle—hardly a justifiable procedure unless in exceptional circumstances.
Clinical Forms of Malarial Fevers
General statements.—The foregoing account, so far as it goes, and so far as it relates to the clinical manifestations produced by uncomplicated and typical infections, is true enough. But, as there may be an infinite variety as regards the number of the parasites present, individual susceptibility, concurrence of several species (mixed infection being far from uncommon), or of several generations of the same species of parasite maturing at different times, there may be a corresponding variety in the clinical manifestations.
In more temperate climates, and in the winter and spring seasons of warmer latitudes, malarial
atmospheric temperature than suffices for the quartan and tertian parasites. Hence, although these two benign and the subtertian parasites are generally found associated together, and the latter can be acquired at any time in the tropics, it is only in the summer or early autumn that it can be acquired in the sub-tropics and temperate zones. It is stated that if the temperature falls below 15° C. the development of the oöcyst in the mosquito is arrested.
