Color-enhanced Transmission Electron Micrograph of T-even phage particles. Left is intact, right has been "triggered." Note condensed tail and extended tail fibers. Bacteriophages are viruses that infect only bacteria. After attachment to the host's surface, viruses inject their complement of RNA or DNA. The host's DNA is instructed to code for bacteriophage replication and within 20 minutes, the progeny is synthesized and wrapped in a protein coat. Magnification: 500,000X at 8 x 10" print size.