Work in progress - more content coming soon...
Remembering which fixative is additive vs. non-additive, and coagulant vs. non-coagulant:
There are basically only 3 non-additive fixatives: acetone, alcohols, and acetic acid. Triple AAA.
That leaves all other fixatives as additives!
Now the harder part: differentiating between coagulants and non-coagulants.
The non-additives are all coagulants. So AAA are all coagulants.
It took me a while to figure out a pattern for the rest, but it seems that all the salts and acids/acidic substances (except for the enigmatic osmium tetroxide) are coagulants:
-mercuric chloride (salt of mercury);
-picric acid;
-chromium trioxide (acidic);
-potassium dichromate (if it’s < 3.4-3.8 pH)
-zinc salts;
-and glyoxal (acidic) (if higher than 4.0 pH, turns into glycolic acid).
That leaves the neutral formaldehyde and glutaraldehyde as non-coagulants, plus the enigmatic osmium tetroxide and potassium dichromate (if it’s in solution with pH > 3.4-3.8).
For potassium dichromate, > 3.4-3.8 pH is NON-acidic and therefore NON-coagulant
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Paraformaldehyde = polymerized, powdered form of formaldehyde
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Glutaraldehyde and formaldehyde are fraternal twins, working via cross-links. But they are fraternal, not identical, because their personalities are opposites:
- Glutaraldehyde --> fast fixation, slow penetration; fixes in 2 hours
- Formaldehyde --> slow fixation, fast penetration; fixes in 6-8 hours
Glutaraldehyde is UNSTABLE and breaks down once it’s exposed to oxygen, much like the green evil witch who breaks down when water is thrown at her.
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Mercury is too mercurial so it’s being replaced by zinc the Zeus. (Mixing up my Greek and Roman gods, but you get the idea.)
If mercury had a personality, it would be the toxic beauty--because while it might be toxic, it leads to beautiful results; and some labs are willing to deal with the toxicity just to acquire that beauty.
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Glyoxal's personality: the overachieving upstart threatening to usurp formaldehyde and glutaraldehyde in every way!
Glyoxal lyses RBCs (because it is acidic, like acetic acid)
Glyoxal not good for H. pylori using silver techniques
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Between picric acid and potassium dichromate, I would forget which one needed to be washed with alcohol and which one with water. So this is how I remembered:
Potassium dichromate's personality: the neglected middle child, therefore it is always crying WATERY TEARS therefore you must WASH THOSE TEARS AWAY WITH WATER (or else angry green pigments will form if exposed to processing alcohol).
So by default, picric acid is the one rinsed with 50-70% alcohol.
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Zinc zings mercury --> Zinc sulfate is common sub for toxic mercury, especially in B-5.
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Bouin's is just:
- picric acid
- formaldehyde
- acetic acid
Gendre's is alcoholic Bouin's:
- 95% alcohol, saturated picric acid
- formaldehyde
- acetic acid
Hollande's is modified Bouin's:
- everything in regular Bouin's PLUS copper acetate to save the RBC's
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If you’ve got your back against a wall, you are on edge!
- so walls are embedded on edge
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Ependymal cells are the real epithelial cells of CNS
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Auramine-rhodamine = stains AFB
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Congo red:
- if sections cut too THICK, it will be like THICK YELLOW MUCUS and therefore will show YELLOW birefringence (this is gross, but the only way for me to remember it)
- The Thin Red Line (like the movie) - if sections cut too thin it shows red birefringence
Sodium chloride in Congo Red prevents background staining
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Maltese cross caused by talcum powder
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WILDER is a WILD ONE so uses phosphomolybdic acid as oxidizer for reticulin, while all others use potassium permanganate
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Weil –> borax ferricyanide is oxidizer to differentiate the stain (Turnbull and Weil –> bull wails)
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Churukian Schenk = citric acid (to provide acid pH for optimal silver staining)
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95% Ethanol subs for cytofixing:
- Methanol is meeker = 100% methanol can sub for 95% ethanol
- Isopropanol is stronger = 80% isopropanol can sub for 95% ethanol
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