When these organs/tissues/fluids are received by the pathology laboratory, they are first placed into formalin to stop them from deteriorating (called fixation). They must then be examined by a medical scientist or anatomical pathologist. The pathologist or scientist will describe any abnormalities in the tissue and then carefully dissect it to aid in diagnosing what disease is present, and to select the areas of the specimen that should be put onto glass slides (processed) for microscopic examination. This initial process of tissue examination is called macroscopic pathology.
The areas of interest within the tissues are cut into small pieces, numbered and labelled and put through a series of procedures to end up with a prepared slide. These steps include dehydrating the tissue, placing it into a wax block to harden it, slicing extremely thin layers off of the block (less than half a millimetre thick), mounting these on a glass slide, staining them so that the tissue will be visible under the microscope and covering them with a cover slip so that the tissue on the slide will be preserved for many years. This process may take one to two days.