Pseudo-PAS

The terms Pseudo-Schiff and Pseudo-PAS refer to the use of dyes other than pararosanilin or basic fuchsin to make a Schiff type solution and use it for demonstrating carbohydrates. While an interesting exercise, it has little practical use except for the occasional demonstration of fungi with a fluorescent pseudo-Schiff solution made with acriflavine. The following dyes, among others, have been suggested.

Dye CI Number Colour     Dye CI Number Colour
Acid fuchsin 42685 violet Acriflavine 46000 yellow
Azure A 52005 blue Azure C 52005 blue
Crystal violet 42555 blue-violet Methyl violet 42535 violet
Methylene blue 52015 blue Safranin O 50240 red
Thionin 52005 blue Toluidine blue 52040 blue

Solutions
1% hydrochloric acid in 70% ethanol
A suitable counterstain

Pseudo-Schiff solution
Prepare a solution according to the instructions for acriflavine Schiff reagent, or another formula, if preferred. Note that they will likely not become colourless, so leave for 48 hours, then filter the solution and store refrigerated.

Tissue sample
5µ paraffin sections of neutral buffered formalin fixed tissue are suitable. Other fixatives are usually satisfactory, although glutaraldehyde should be avoided.

Method

  1. Bring sections to water via xylene and ethanol.
  2. Place into periodic acid for 10 minutes.
  3. Wash with running water.
  4. Rinse with distilled water.
  5. Place in pseudo-Schiff's reagent for 10-30 minutes.
  6. Rinse with distilled water.
  7. Place in acid ethanol for 5 minutes.
  8. Wash well with tap water for about 10 minutes.
  9. Counterstain with a suitable contrasting nuclear stain.
  10. Dehydrate with ethanol, clear with xylene and coverslip using a resinous medium.

Expected results

Notes

  1. Glutaraldehyde fixation leaves free aldehyde groups attached to tissues, which causes an overall positive reaction. These groups may be stopped from reacting with an appropriate procedure such as the aniline-acetic aldehyde block.
  2. The treatment with acid ethanol at step 7 is to ensure that unreduced dye in the pseudo-Schiff reagent does not stain tissues ionically.
  3. The tap water wash at step 8 is necessary to develop the colour. Within limits, the longer the wash the darker the colour.

 

Reference
Culling C.F.A., (1963)
Handbook of histopathological and histochemical techniques Ed. 2
Butterworth, London, UK.

 


 

 

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