Transmission electron micrograph of the trophozoite, or proliferative form, of the sporozoan ^IToxoplasma ^Igondii^i. They appear as the large dark stained bodies enclosing numerous organelles. ^IT. gondii^i causes toxoplasmosis in humans & is especially dangerous to pregnant women. Cats are the definitive host and all mammals including sheep & cattle may become infected. Only cats excrete the oocysts in their faeces, which contaminate the soil & cause the infection in humans & animals. Infection in man also occurs through undercooked meat, or direct contact. Magnification: x20,000 at 8x10 inch size.