Loose ends: axenic culture, parasitophorous vacuoles, bird malaria.

The successful extracellular cultivation of the erythrocytic stages of Plasmodium falciparum is briefly summarized, with a discussion of its implications. This leads to consideration of the roles of the parasitophorous vacuole and its membrane and of the tubulo vesicular network. It is concluded that these structures are mainly concerned with modification of the host erythrocyte for the benefit of the parasite. Requirements for additional nutritional factors under axenic culture conditions are also considered with special reference to erythrocyte membrane protein and to pantothenate. Finally, attention is given to speculations on the origin of P. falciparum.