Sometimes histology is performed for the purpose of education or publication. The field of pathology often includes histology because histology is required for many pathological diseases to be identified.
Commonly the term histology refers to the preparation of tissue for light microscopy. Electron microscopy is also common for specific tissue components that are too small to refract light under a light microscope. Due to the very high expense, electron microscopy is not performed if a light microscope can be used to obtain the results.
The most common histology procedures are performed on paraffin infiltrated and embedded tissue. The paraffin infiltration process of creating a histology slide for examination denatures proteins and eliminates almost all lipids (fat) in the tissue. When those specific proteins or lipids are of interest, the tissue is not paraffin processed. Instead it is frozen and cut on a cryostat (similar to a microtome but is kept at temperatures below freezing). Very low quality images are produced to study, this is due to the nature of water in the tissue freezing and expanding within each cell. Commonly half of a histology specimen is paraffin processed, and the other half is frozen so that both techniques can be performed.
Histology takes many years to master. Histotechnologist are one of the most important behind the scenes lab technicians in modern medicine. Since the beginning of histological studies, much has changed and much has stayed the same! Many new techniques have been introduced, as well as many new equipment designs. The basic idea of cutting something thin enough to allow the passage of light will always be the basis of histology. Cutting it well, flat and clean without damage from the knife is a very important part of histology. Some specimens cut very easily, others break in half and go flying across the workbench.
There is a small amount of danger in histology for most procedures, and some procedures involve a higher level of danger. You have to pay close attention when using equipment such as a microtome or when mixing chemicals and solvents. The glass of a slide can be very sharp when broken, and the glass cover slips can cut through a glove easily since they are so thing. Microtome blades are constantly being changed out, you must always remember to clamp it in firmly and to remove it when cleaning.
Cryostats operate around minus twenty Celsius usually, sometimes colder or warmer but that is a good medium range. At this temp, your hands can get cold enough to hurt and cause some longer term damage. Due to fatigue many techs will rest a hand on a very cold piece of metal within the cryostat, they hardly notice the cold after working in a cryostat for several hours. Most of the tissue being cut in a cryostat is not fixed and therefore more challenging This creates a high risk factor for potential infection from exposure during normal cryo-sectioning or if the tech gets a cut from the blade.