Page:Popular Science Monthly Volume 58.djvu/373

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 during any time but just before, during, or soon after rigor. If we wish to see the early and unpigmented forms, we must look for them during the later stage of rigor or the earlier part of the stage of pyrexia. And so with the other stages of the parasite; each has its appropriate relationship to the fever cycle."

There are numerous cases of malarial fever in which there is no distinct intermission and in which the course of the fever is either continued or remittent in character. Fevers of this type usually occur in the late summer or in the autumn (æstivo-autumnal) and are believed to be due to infection by two distinct varieties of the parasite; one, the tertian æstivo-autumnal, causes a fever characterized by a marked rise in the temperature every second day; the other, a fever in which there is a daily elevation of temperature. There are certain peculiarities relating to the intra-corpuscular development of these parasites which enable us to differentiate them from the tertian and quartan parasites of intermittent fever, but a more striking difference to be observed in their life cycle of development in the blood of man is the presence of peculiar crescentic-shaped bodies, which play an important part in their further development in the body of an intermediate host—the mosquito. Associated with these 'crescents' fusiform and ovoid bodies are often seen which are no doubt similar in their origin and function. The crescents are a little longer than the diameter of a red blood corpuscle and are about three times as long as broad. They contain in the central portion grains of pigment (melanin) derived from the hæmoglobin of the infected corpuscle which has been changed into a crescentic body as a result of the development of the malarial parasite in its interior. When a fresh preparation of malarial blood containing these crescents is observed under the microscope, while a majority of them retain the crescentic form, others may be seen, after an interval of ten minutes or more, to change in form, first becoming oval and then round; then, in the interior of these round bodies an active movement of the pigment granules occurs; this is followed by the thrusting forth from the periphery of several filaments—usually four, which have flagella-like movements. These, as a rule, become detached and continue to move rapidly among the blood corpuscles. With reference to the function of these motile filaments, Marchiafava says:

"In these later days there is increasing belief in the theory, which we uphold, that the crescents and the flagellata are sexual forms of the malarial parasite, and that a reproductive act (in which the flagellum represents the male element and an adult crescent the female cell) gives rise to the new being which begins its existence in the tissues of the mosquito.

These crescentic bodies may be found in the blood of man long after all febrile symptoms have disappeared, and it is generally recognized