Transmission electron micrograph of Chlamydia psittaci bacteria inside a lung cell. The pale area filling most of the photograph is an inclusion body which contains bacteria at different stages in their life cycle. In the top left corner is the cell's nucleus with its darkly- stained chromatin. Various other organelles can be seen within the cell. Chlamydia species are atypical bacteria in that they are obligate intracellular parasites, living and reproducing only inside cells. This species causes abortion and lung disease in humans. Magnification: x21,000 on 8x10 print."