False colour transmission electron micrograph (shadowed) of a T4 bacteriophage, a virus that infects only bacteria, in this case only Escherichia coli. Phages lack any reproductive machinery & rely on the apparatus of bacteria in order to replicate. They do so by attaching to the cell wall of the bacterium using the spidery tail fibres visible here. The tail is a contractile sheath, which contracts, injecting the contents of the head, the genetic material (DNA) into the cell. The genetic apparatus of the host is commandeered & within 20 minutes progeny fill the cell. Magnification: X60,000 at 35mm size. orginal is Bw print m090/019