MICRO-STRUCTURE ANALYSIS OF PLANT TISSUES - Lublin

only at very acute angles. In this situation the light rays passing through the slide
do not enter the objective; what does enter the objective is light deflected
or reflected by particles contained in the specimen (Fig.2.6). The particles are
then seen as small fluorescent dots against a darker background. The dark field
method is used mainly for the observation of micro-organisms in body fluids [3,
8, 14].
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3
4
Fig. 2.6. Image generation in dark field, 1 – objective lens, 2 – stage, 3 – condenser lens,
4 - light.
Phase-contrast microscope: The retina of the human eye reacts to two out
of three physical parameters of light wave – the length of the wave, perceived
as colour, and its amplitude, perceived as the degree of brightness. The third
parameter – phase – is not registered by the retina, although it is also subject
to modification during the transition of light through the microscope slide.
The various structures present in the specimen observed cause different shifts
in the light wave phase. This phenomenon has been utilized in the design
of the phase-contrast microscope, by introducing a special optical system that
transforms the light wave phase shift into a change in its amplitude (Fig. 2.7), [4,
6, 14].
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