Use this microscope slide to examine the structure of the active trophozoite form of Giardia lamblia. This flagellated, parasitic protozoan causes giardiasis, an infection of the human small intestine characterized by diarrhea and abdominal pain. The parasite exists in 2 forms: the inactive cyst and the active trophozoite that colonizes the small intestine. The trophozoites typically have paired nuclei and paired flagella. Stained with Heidenhain's hematoxylin.