Fixatives Flashcards
If acidic (unbuffered), a dark brown precipitate may form in vascular tissue
Formalin
Fast penetration rate but fixation is slow
Formalin
Addition of methanol can reduce polymerization of this fixative
Formalin
May cause diffuse PAS reaction due to unbound aldehyde group
Glutaraldehyde
Yellow precipitate can be prevented by washing tissue prior to dehydration
Potassium dichromate
Tissues are left soft if used alone, so it is used as part of a compound fixative
Potassium dichromate
If concentrated form is purchased, it must be diluted to 10% (w/v) for use
Formalin
Its precipitate is difficult to remove but can be reduced with 1% acid alcohol
Potassium dichromate
While commonly used for routine fixation, it is a known carcinogen
Formalin
Its mode of action differs above and below pH 3.75
Potassium dichromate
It is used almost exclusively for electron microscopy, as it preserves the ultrastructure
Glutaraldehyde
It forms a black precipitate throughout the tissue
Mercuric chloride
Used as a component of compound fixatives in the fixation of blood films, cytology smears and enzymes for histochemistry
Ethyl alcohol
Its precipitate can be removed using alcoholic iodine followed by sodium thiosulfate
Mercuric chloride
As a component of a compound fixative its swelling effect can counteract shrinkage
Acetic acid
Its yellow coloration is easily removed in the dehydration step
Picric acid
Extremely volatile and can fix nasal mucosa wishing minutes of exposure
Osmium tetroxide
It is extremely toxic affecting the CNS and can cause acute nephritis
Mercuric chloride
Can be used to store tissue for extended periods of time
Formalin
Its precipitate can be removed with alcoholic picric acid
Formalin
Is inexpensive, stable, and tolerant
Formalin
Its use results in layer fixation and causes pronounced shrinkage
Mercuric chloride
Explosive when dry
Picric acid
This will fix lipids and blacken them microscopically
Osmium tetroxide
Its precipitate can be removed with 2% ammonia in 80% alcohol
Formalin
