Transmission electron micrograph of bacteriophage T4 (virus infecting bacteria), 60 minutes after the injection of its viral DNA into the bacterium Escherichia coli. The phage, specific to E.coli, is secured to the surface by means of spidery tail fibres. The tail, a contractile sheath, shortens to allow a syringelike tube (visible below base plate of tail) to penetrate the cell membrane, emptying the DNA contents of the head into the bacterium. The capsid, a protein coat surrounding the DNA, remains outside the cell. Synthesis & assembly of the phage within the cell follows rapidly. Mag: X220,000 (at 10x8 size).