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The Role of the Histopathology Department at the Central Health laboratory

Histology is the microscopic study of tissues of living organisms. The Histology Department of the Central Laboratory at Candos is mainly concerned with the examination of diseased tissues and the diagnosis of cancer in patients from all hospitals and clinics of Mauritius and Rodrigues. The procedures adopted for the preparation of materials for microscopic examinations are known as histological techniques and it is with these techniques that the Medical Laboratory Technicians in the Histology Department are primarily concerned.

The various ways of preserving and processing tissues, cutting and staining sections and the ability to recognize whether or not the procedures have been performed correctly constitute the skill of the histology technician. For the work to be performed competently, knowledge of the complex histological structure of tissues to be examined is essential.

The Suspected part of the tissue is cut and processed in wax and thin sections are cut using a microtome.

Cutting sections on the microtome is comparatively very easy. The sections still embedded in wax are floated on the surface of a waterbath heated to 50 C. to remove all wrinkles and then mounted on glass slides. The sections are dried on a hot plate. Before staining, the sections are de-waxed in xylene.

An entirely different approach is to freeze the tissue solid by liquid Nitrogen or Carbon dioxide and then sections cut using a freezing microtome or cryostat. The frozen sections produced in this way are important when time does not permit the production of wax sections as the patient is on the operating table and the nature of the lesion must be determined urgently. They are also needed to demonstrate the presence of materials such as fats and enzymes, which might be destroyed in wax techniques.

Most unstained tissues are almost transparent and the recognition of specific structures is difficult as all the various components of a tissue have more or less the same refractive index. Hence, there is no contrast. The purpose of staining is to render prominent the different tissue elements so that they may be easily recognized and studied.

The tendency nowadays is towards selective or differential staining by which tissue can recognise elements morphologically similar. The staining technique most commonly used in histology is " Haematoxylin and Eosin" which stains nuclei blue and other tissue elements shades of pink.

Histology has contributed a great deal to the advancement of science. It has become one of the most widely used research and diagnostic technique available to biology and medicine. It has found widespread use in medical research whenever direct observation of normal or pathological disease is required. It is very important for the diagnosis of cancer. About 8000 specimens are processed annually at the Central Lab, out of which about 12% turns out to be malignant.

Histology is widely used during the prolonged tests of drugs and cosmetics in order to determine their effects in the user. It is being used by the food processing industries to investigate changes within the tissues of stored food.

In the coming years, automation will increase the usefulness of Histology by making the many steps involved in processing a specimen cheaper and faster. Already processing and staining machines are in use. Staining methods will become more precise as more is learned about the chemistry of the cell. The expanding field of histochemistry and immunocytochemistry could become more diagnostic as we learn more about the chemical constituents of normal and diseased cells.