58 PART III Sample Preparation in Light Microscopy
methods can all be applied to paraffin sections. In most cases, the produced slides
are completely stable and can be kept for many years.
Just in case you are a fan of Campari – the alcoholic liqueur contains
carminic acid. The intensely red dye is extracted from dried, pulverized
bodies of certain female scale insects, Dactylopius coccus, which
are cactus-eating insects native to tropical and subtropical America.
You can use this natural dye also for different stainings. Cheers!
Papanicolaou Staining
Probably you know this method as pap-staining or pap-smear. It was developed
in 1928 by George N. Papanicolaou and is one of the standard techniques in gynecology
to detect precancerous and cancerous cells in the cervix. Pap-staining is
used for fixed wet mount samples. Typical is the transparent appearance of the
cytoplasm, which also allows the visualization of cells in overlaying parts. To stain
the nuclei, you use hematoxylin. To stain the cytoplasm, you use dye mixtures
consisting of eosin, azure and the azo dye orange G. These mixtures are available
as ready-to-use stain and you don’t need to play around by yourself.
Giemsa and Wright Staining to Reveal
Blood Components
When staining blood, either Pappenheim, Giemsa, Wright or Romanowsky stain
are used, or a combination thereof. In most cases, simply Wright’s stain is used.
Red blood cells will stain pink, platelets appear blue/purple and cytoplasmic granules
stain pink to violet. White blood cells include granulocytes (neutrophils,
eosinophils and basophils) and agranulocytes (lymphocytes and monocytes).
Neutrophils are displayed as a deep blue/purple nucleus under the microscope.
Gram Stain for Bacteria
The Gram stain is a method for staining bacteria that was developed in 1884 by the
Danish bacteriologist Hans C. Gram and differentiates between Gram-positive
and Gram-negative bacteria. This process makes it possible to identify the different
types of bacteria and visualize their morphology with an optical microscope.
Gram staining is an important part of the diagnosis of infectious diseases, as
Gram-positive and Gram-negative bacteria have a different cell wall composition
and thus require treatment with different antibiotics.