Microscopy

Histology 2016-2017
Department of Anatomy &Histology: Dr.Rajaa Ali
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MICROSCOPY
Once the paraffin sections are stained with haematoxylin and eosin (H&E) or with some special stains, it can be viewed through a light microscope. Its various parts and their functions are enumerated in Practical No. 1. Moreover, it is important that the student should have the basic knowledge of the principles of some special microscopes that are being used under
certain condition.

Basic Principles of Some Special Microscopes
Dark Ground (Dark Field) Microscope
Dark-ground microscope is a modifi ed light microscope where the objects are examined by dark ground illumination.
Dark ground illumination is obtained simply by inserting a small circle of black paper in the centre of the fi lter carrier of the condenser. The central rays which would normally pass through the object and into the objective are cut off and the peripheral rays from the condenser pass through the object, but do not enter the objective; the only light entering the objective will be
that scattered (refracted) by the object, which makes the object bright and self-luminous against a dark background with a high degree contrast.
This microscope is used to examine extremely minute particles (colloid suspension) or large transparent objects (e.g. living protozoa, crystals, etc.) which are otherwise invisible with ordinary light microscope. This phenomenon is similar to the appearance of dust particles fl oating in a beam of sunlight in a dark room.

Phase-contrast Microscope
This microscope has been developed based on the fact that light passing through any transparent object mounted in a medium of a different refractive index slows down and changes its direction. Within the cell, different organelles exhibit different refractive indices and consequently alter the phase of the light that passes through them to different extents.