How sensitive is the light microscope for observations on microorganisms in natural habitats?
Theoretical calculations based on the depth of field of standard microscope objectives and the visual acuity of normal observors show that direct microscopy of natural samples is rarely able to reveal the presence of small microorganisms at the densities found in natural systems. Over-estimation of the importance of bacterial aggregates is also likely from an uncritical use of light microscopy.
Department of Bacteriology, University of Wisconsin-Madison, 53706, Madison, Wisconsin, USA.
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Brock