Aqueous Gum 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 which 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.

Apathy  
Water
Gum arabic
Fructose
30
30
30
mL
g
g
 • Dissolve gum arabic in water with gentle heat.
 • Add fructose and mix well.
 • Avoid vigorous agitation to avoid bubbles.
 • 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.
Farrants  
Water
Glycerol
Gum arabic
40
20
40
mL
mL
g
 • Dissolve the gum arabic in warm water.
 • Add the glycerol and mix well.
 • Avoid vigorous agitation to avoid bubbles.
 • 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.
 
The column headings refer to:–

Water
Glycerol
Gum
refers to distilled water
refers to 99.5% glycerol
refers to gum arabic
Variant Water Gum Glycerol Other
Chevalier 60 20 20
Davies 30 30 30 Arsenic trioxide 0.1 (or thymol crystal)
Hogg 75 25 Phenol 5
Langerhaus 20 60 25 Phenol 1
Martin 50 50 25 Camphor 0.2 (or thymol crystal)
Robin I 45 15 30
Robin II 100 50 50
Variant Water Gum Sugar Other
Highman 50 25 Sucrose 25 Potassium acetate 25 or sodium chloride 10
Landau 30 30 Glucose 35
Lillie & Ashburn 100 50 Sucrose 50 Thymol 0.1

 

Reference
Gray, Peter. (1954)
The Microtomist's Formulary and Guide. pp. 631.
Originally published by:– The Blakiston Co.
Republished by:– Robert E. Krieger Publishing Co.

Carleton, H M, and Leach, E H, (1938)
Histological Technique, 2nd ed.
Oxford University Press, London, England


 

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