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Gum Arabic Mountants

Gum Arabic Mountants

Gum arabic is obtained from two species of acacia tree, and is also known as gum acacia for that reason. It is water soluble and forms a thick, syrupy solution that is suitable as the basis for aqueous mounting media. It is a mixture of compounds, mostly carbohydrates, and is not chemically pure so its composition may vary from sample to sample. Since it is a natural product, it may also contain dirt. If so, it may be dissolved in water and filtered through glass wool. Quite commonly, mounting media made from gum arabic also contain high concentrations of a sugar, often glucose, fructose or sucrose.

Both Apathy’s and Farrants’ mounting media are commonly used. Both are suitable for coverslipping lipid stains, and are recommended. Both are available commercially, and most laboratories purchase premade solutions rather than make their own. There is also a variant of Apathy’s suitable for mounting metachromatic stains (Highman – see list below), usually not advised with sugar gum mixtures due to leaching of the dye.

The list of media below is not exhaustive. Due to the sugar and gum content they should contain a preservative, and a small crystal of thymol is probably the most convenient. In the list, all numbers refer to grams if a solid and milliliters if a fluid.

Formula

MaterialAmount
Water30mL
Gum arabic30g
Fructose30g

Procedure

  1. Dissolve gum arabic in water with gentle heat.
  2. Add fructose and mix well.
  3. Avoid vigorous agitation to avoid bubbles.

Notes

  • A small crystal of thymol may be added as a preservative.
  • Gray replaces fructose crystals with fructose syrup and reduces the water to 20 mL.
  • Drury & Wallington use sucrose instead of fructose.
MaterialAmount
Water40mL
Glycerol20mL
Gum arabic40g

Procedure

  1. Dissolve the gum arabic in warm water.
  2. Add the glycerol and mix well.
  3. Avoid vigorous agitation to avoid bubbles.

Notes

  • Preserve with a little camphor, phenol or thymol.

The list of media below is not exhaustive. Due to the sugar and gum content they should contain a preservative, and a small crystal of thymol is probably the most convenient. In the list all numbers refer to grams if a solid and millilitres if a fluid.

VariantMaterial
Distilled water Gum arabic99.5% glycerolOther
Chevalier60 mL20 g20 mL
Davies30 mL30 g30 mLArsenic trioxide 0.1 g (or thymol crystal)
Hogg75 mL25 gPhenol 5 g
Langerhaus20 mL60 g25 mLPhenol 1 g
Martin50 mL50 g25 mLCamphor 0.2 g (or thymol crystal)
Robin I45 mL15 g30 mL
Robin II100 mL50 g50 mL
VariantMaterial
Distilled water Gum arabicSugarOther
Highman50 mL25 gSucrose 25 gPotassium acetate 25 g or sodium chloride 10 g
Landau30 mL30 gGlucose 35 g
Lillie & Ashburn100 mL50 gSucrose 50 gThymol 0.1 g

Safety Note

Prior to handling any chemical, consult the Safety Data Sheet (SDS) for proper handling and safety precautions.

References

  1. Gray, Peter. (1954)
    The Microtomist’s Formulary and Guide. pp. 631.
    Originally published by:– The Blakiston Co.
    Republished by:– Robert E. Krieger Publishing Co
  2. Carleton, H M, and Leach, E H, (1938)
    Histological Technique, 2nd ed.
    Oxford University Press, London, England