The classical way of studying biological material in a light microscope is to fix and stain the specimen and then to cut it up into thin slices for examination in the microscope. However, if thick slices or whole-mounts are examined, structures in the interior of the specimen are usually obscured by interference from structures at either side of the plane of focus. Techniques have been developed that enable whole-mount samples to be examined by optical sectioning. These techniques all function to minimise or eliminate this out-of-focus interference. Optical sectioning microscopy permits the internal three dimensional structure of living tissue to be visualized.

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