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Unformatted text preview: Viral measurements. Viruses are generally too small to be seen under the light microscope, and an electron microscope is usually necessary to make them visible. Although viruses can be quantified by observation, it is also possible to determine their number in terms of virus infectious units, each of which is the smallest unit that causes a detectable effect when viruses infect a susceptible host. Virus infectious units are expressed per volume of fluid. One method for determining virus infectious units is by the plaque assay. The plaque assay is performed by cultivating viruses on a lawn of host cells and noting the presence of clear areas where viruses have replicated and destroyed the cells. Another way of determining virus infectious units is by cultivating viruses in living animals and determining which dilution of virus is lethal to the animals. The end-point dilution can be calculated determining which dilution of virus is lethal to the animals....
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- Fall '07