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Bright-field, dark-field, and fluorescence microscopy. A. Bright-field illumination properly aligned. The purpose is to focus light directly on the preparation
for optimal visualization against a bright background. B. In dark-field illumination, a black background is created by blocking the central light. Peripheral
light is focused so that it will be collected by the objective only when it is reflected from the surfaces of particles (eg, bacteria). The microscopic field shows
bright halos around some bacteria and reveals a spirochete too thin to be seen with bright-field illumination. C. Fluorescence microscopy is similar to darkfield microscopy, except that the light source is ultraviolet and the organisms are stained with fluorescent compounds. The incident light generates light of
a different wavelength, which is seen as a halo (colored in this illustration) around only the organism tagged with fluorescent compounds. For the most
Source: Chapter 4. Principles of Laboratory Diagnosis of Infectious Diseases, Sherris Medical Microbiology, 5e
common fluorescent compound, the light is green.
Citation: Ryan KJ, Ray C. Sherris Medical Microbiology, 5e; 2010 Available at: Accessed: August 11, 2017
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