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
