Histological

Histology

Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...

 section refers to thin slices of tissue

Biological tissue

Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

 applied to a microscopic slide, usually around 5 to 10 micrometre

Micrometre

A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

s thick, which are viewed under a microscope

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

. For further discussion of histological section and staining methods, one should review histology

Histology

Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...

 article.

Gross cutting

The specimen is cut into the correct size and configuration prior to fixation and microtome cutting. The specimen is stained and positioned for proper orientation. With Mohs surgery

Mohs surgery

Mohs surgery, also known as chemosurgery, created by a general surgeon, Dr. Frederic E. Mohs, is microscopically controlled surgery used to treat common types of skin cancer. It is one of the many methods of obtaining complete margin control during removal of a skin cancer using frozen section...

 or the CCPDMA

CCPDMA

CCPDMA is the acronym for "complete circumferential peripheral and deep margin assessment". It is the preferred method for the removal of certain cancers, especially skin cancers.A classical example of CCPDMA is Mohs surgery...

 method of cutting, the specimen is cut in a manner to allow mounting all of the surgical margins on one plane. With standard bread loafing

Bread loafing

Bread loafing is a common method of processing surgical specimen for histopathology. The process involves cutting the specimen into 3 or more sections. The cut sections are mounted by embedding in paraffin or frozen medium. The cut edge is then thinly sliced with a microtome or a cryostat...

, the specimen is usually cut into multiple sections with the surgical margin stained. Some technologist will stain the edge to be oriented toward the microtome. The cut specimen is then transferred directly to frozen medium for frozen section processing, or placed in small cassettes for dehydration and paraffin embedding.

Fixation

Fixation

Fixation

Fixation may refer to the following:In science:*Fixation , the state in which an individual becomes obsessed with an attachment to another human, an animal, or an inanimate object...

 is done either by the fixed tissue method with paraffin, or by frozen section. With fixed tissue method, the tissue specimen is preserve in either formaldehyde or an acidic solution until it is processed. The tissue is then removed from the preservative, dehydrated with multiple solvent baths, and fixed in hot liquid parafin. The hardened parafin block with the fixed tissue is then cut with the microtome

Microtome

A microtome is a sectioning instrument that allows for the cutting of extremely thin slices of material, known as sections. Microtomes are an important device in microscopy preparation, allowing for the preparation of samples for observation under transmitted light or electron radiation...

. With frozen tissue sectioning, the tissue is immediately frozen prior to processing (frozen section).

Microtome Cutting

The frozen tissue block embedded in a frozen cutting medium, or the paraffin fixed tissue is cut using a very fine knife called a microtome

Microtome

A microtome is a sectioning instrument that allows for the cutting of extremely thin slices of material, known as sections. Microtomes are an important device in microscopy preparation, allowing for the preparation of samples for observation under transmitted light or electron radiation...

. A cryostat

Cryostat

A cryostat is a device used to maintain cold cryogenic temperatures. Low temperatures may be maintained within a cryostat by using various refrigeration methods, most commonly using cryogenic fluid bath such as liquid helium. Hence it is usually assembled into a vessel, similar in construction...

 is a micotome mounted inside a freezer for processing frozen tissue.

Mounting

The frozen thin slices of tissue are mounted on a warm glass slide at room temperature, or the paraffin embedded slides are mounted on a heated glass. This allow them to be stained and ready for staining. The tissue mounted slides are then dry in open air or in a drying oven.

Staining and coverslipping

Multiple stain baths are used to make the tissue more visible to the naked eye. Please see histology

Histology

Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...

 for discussion of the stains used. Sections usually have a very thin piece of glass applied over the surface called a cover slip

Cover slip

A cover slip or cover glass is a thin flat piece of transparent material, usually square or rectangular, about 20 mm wide and a fraction of a millimetre thick, that is placed over objects for viewing with a microscope...

. The glass cover slip is glued onto the slide with a special optical grade transparent glue.

Common laboratory stains

Stain	Common use	Nucleus	Cytoplasm	Red blood cell (RBC)	Collagen fibers	Specifically stains
Haematoxylin Haematoxylin Haematoxylin, hematoxylin, Natural Black 1, or C.I. 75290 is extracted from the heartwood of the logwood tree. When oxidized it forms haematein, a compound that forms strongly coloured complexes with certain metal ions, the most notable ones being Fe and Al salts. Metal-haematein complexes are used...	General staining when paired with eosin (i.e. H&E)	Blue	N/A	N/A	N/A	Nucleic acids—blue ER (endoplasmic reticulum)—blue
Eosin Eosin Eosin is a fluorescent red dye resulting from the action of bromine on fluorescein. It can be used to stain cytoplasm, collagen and muscle fibers for examination under the microscope. Structures that stain readily with eosin are termed eosinophilic....	General staining when paired with haematoxylin (i.e. H&E)	N/A	Pink	Orange/red	Pink	Elastic fibers—pink Collagen fibers—pink Reticular fibers—pink
Toluidine blue	General staining	Blue	Blue	Blue	Blue	Mast cells granules—purple
Masson's trichrome stain	Connective tissue	Black	Red/pink	Red	Blue/green	Cartilage—blue/green Muscle fibers—red
Mallory's trichrome stain	Connective tissue	Red	Pale red	Orange	Deep blue	Keratin—orange Cartilage—blue Bone matrix—deep blue Muscle fibers—red
Weigert's elastic stain Weigert's elastic stain Weigert's elastic stain is a combination of stains used in histology which is useful in identifying elastic fibers. Often orcein or a combination of resorcinol and fuchsine are used for staining. For counterstaining cell nuclei nuclear fast red or hematoxylin is also used. After applying elastic...	Elastic fibers	Blue/black	N/A	N/A	N/A	Elastic fibers—blue/black
Heidenhain's AZAN trichrome stain Heidenhain's AZAN trichrome stain Trichrome stains are staining methods in which three anionic dyes are used, in conjunction with either phosphomolybdic acid , phosphotungstic acid , or a mixture of these heteropolyacids. Probably the first trichrome method was that of Frank B Mallory, an American pathologist, first published in 1900...	Distinguishing cells from extracellular components	Red/purple	Pink	Red	Blue	Muscle fibers—red Cartilage—blue Bone matrix—blue
Silver stain Silver stain Silver staining is the use of silver to selectively alter the appearance of the target.-Use in medicine:It is used to stain histologic sections. This kind of staining is important especially to show proteins and DNA. It is used to show both substances inside and outside cells...	Reticular fibers, nerve fibers, fungi	N/A	N/A	N/A	Reticular fibers—brown/black Nerve fibers—brown/black
Wright's stain Wright's stain Wright's stain is a histologic stain that facilitates the differentiation of blood cell types. It is used primarily to stain peripheral blood smears and bone marrow aspirates which are examined under a light microscope...	Blood cells	Bluish/purple	Bluish/gray	Red/pink	N/A	Neutrophil granules—purple/pink Eosinophil granules—bright red/orange Basophil granules—deep purple/violet Platelet granules—red/purple
Orcein stain	Elastic fibres	Deep blue [or crazy red]	N/A	Bright red	Pink	Elastic fibres—dark brown Mast cells granules—purple Smooth muscle—light blue
Periodic acid-Schiff stain (PAS)	Basement membrane, localizing carbohydrates	Blue	N/A	N/A	Pink	Glycogen and other carbohydrates—magenta

Table sourced from

The Nissl method and Golgi's method

Golgi's method

Golgi's method is a nervous tissue staining technique discovered by Italian physician and scientist Camillo Golgi in 1873. It was initially named the black reaction by Golgi, but it became better known as the Golgi stain or later, Golgi method.Golgi' staining was famously used by Spanish...

 are useful in identifying neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s.