Scanning electron micrograph of the bloodstream form of a trypanosome (yellow) among the host red blood cells (in this instance, those of a mouse). Here, the trypanosome has two flagella, suggesting that it is in the process of dividing. Trypanosoma brucei brucei is a parasite that causes sleeping sickness. The sample was prepared by fixing cultures with 2 percent glutaraldehyde and then dried using CO2. Supplied by Gull Lab/Samantha Griffiths, courtesy of Wellcome Images.