False-colour transmission electron micrograph of a cluster of P1 bacteriophages. Bacteriophages are viruses that infect only bacterial cells. P1 is a temperate phage (lysogeny) which means it is non virulent, does not multiply, or cause lysis (cell death by bursting). Instead its DNA attaches to the bacterium's & is passed on at each division. The attached condition is known as the prophage state. Phage DNA is contained within the head (orange sphere), a 20-faced (icosahedron) figure. The head is attached to a tail, a contractile sheath, which injects the DNA into the bacterium through a syringe-like tube (seen here). Magnification:x185,000 at 10x8, x52,857 at 6x7cm.