The simultaneous inoculation of two patients with both P. vivax and P. falciparum is reported. In one instance each parasite was in a separate lot of mosquitoes; in the other at least some of the mosquitoes employed were simultaneously infected with both species of parasite.
Both simultaneous inoculations were successful, although the center of the stage in each case was immediately assumed by P. falciparum. This parasite was the first to increase to densities in excess of the microscopical level, and the early clinical reactions displayed the characteristics of the disease which it initiates. P. vivax was observed only intermittently and sparsely during this time. When it did start to increase significantly, P. falciparum rapidly decreased, and the former species ultimately attained moderate densities and produced a characteristic clinical attack. This succession suggests an antagonism between the species.
In one instance falciparum reappeared, and both parasites remained for some time at a relatively low and approximately equal density.
Attention should be called to the relation which the appearance of falciparum gametocytes bears to the original attack or a recurrence, which is well brought out in each chart.
Autochthonous cases, probably from the element of chance alone, most commonly represent inoculation with but a single species of parasite. Multiple inoculation is possible, however, and results in an interesting clinical situation.