In histology, slices of biological tissue or cells are stained to provide contrast and highlight interesting features under a light or electron microscope.

This section covers:

International standards and resources

The World Association of Veterinary Anatomists publishes histology terminology for animals in Nomina histologica veterinaria.


Haematoxylin and eosin stain (H&E stain; sometimes referred to as HE stain) is the most commonly used stain for light microscopy in histology and histopathology. Hematoxylin, a basic dye, stains nuclei blue; eosin, an acidic dye, stains the cytoplasm pink. Erythrocytes appear red.

Stain names are lower case unless they are named after a person, in which case a possessive s is not used:

toluidine blue     orcein stain     Masson trichrome stain     Wright stain

Some stain names are commonly abbreviated:

periodic acid–Schiff (PAS) stain [also note the en dash in this name]

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Bacterial staining

Gram staining, or Gram method, is used to differentiate bacteria into 2 main groups – those with and those without a thick cell wall. Crystal violet is used to stain the bacteria; those with a thick cell wall retain the dye (positive), whereas those without this type of cell wall do not retain the dye (negative). A counterstain – usually safranin or fuchsine – is also used to colour both bacteria types.

Did you know? Gram staining is named after a Danish physician and bacteriologist, Hans Christian Gram, who discovered, in 1884, that crystal violet stains some bacteria but can be washed out from others.

Use an initial capital when referring to the stain or method, but lower case for adjectival (eponymic) forms:

Gram stain     gram-negative bacteria

See also Terms derived from proper nouns.

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Names of microscopic techniques and equipment are not capitalised even if abbreviated to capital letters:

light microscopy     transmission electron microscope (TEM)     scanning electron microscope (SEM)

To show magnification, use a multiplication symbol (not the letter x) after the number (no space):

7,500×     10×

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