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2 In 1847 Meckel described certain pigment-bearing cells which he had found in the spleen and in the blood at the post-mortem of a patient who had died of malaria. Virchow was able to confirm this observation, and Planer in 1854 noted these pigmented cells in fresh blood from the finger of malarial patients. These cells were, of course, the malarial parasites, although their true nature was not apprehended at the time.

The parasitic nature of malaria, which had been suspected since the days of Varro and Columella, was definitely established by Laveran, who in 1880, having noticed the eruption of long motile filaments from the pigmented cells described by Meckel and Planer, was the first to recognize their parasitic character.

Laveran's observations were soon extended by Marchiafava, Celli, Golgi, Bignami, Bastianelli, and other investigators, but especially by Golgi, who demonstrated the definite correlation between the development of the parasites and the periodicity of the fever paroxysms, and showed that the different types of malarial fever correspond to different species of parasites.

The association of the malarial parasites with certain mosquitoes, suggested by epidemiological facts, and by certain phases in the life-history of the parasite indicating the necessity of alternation of generations, together with a change of host as in other haemoparasites, was definitely established by Ross's investigations and the experiments carried out by the Italians and ourselves.

Finally, the application of these recent discoveries to the diagnosis and prevention of malaria has led to practical measures which have already been fruitful in good results and promise yet more.

It is now placed beyond doubt that the presence and proliferation in the blood of these parasites are the cause of what was formerly and is still known as "malarial disease." The following is a