This slide shows a blood smear containing the flagellate Trypanosoma brucei that causes African sleeping sickness in humans.  Although there are two subspecies of the parasite that cause slightly different forms of the disease, both are transmitted by the bite of the tsetse fly (Glossina). Numerous purple-stained trypanosomes (pointed to by the blue arrows) can be seen among the lightly stained, circular erythrocytes (red blood cells).  A large, darkly stained lymphocyte (white blood cell) can also be seen on the slide.