Chapter Index

Chemicals used for preservation of carcasses and samples
First unrevised draft. Help for improvement would be appreciated

For fixing of tissues for histology
For histological studies, buffered neutral formalin is a good general purpose fixative. For certain histological procedures, however, other fixatives may be better because they penetrate tissues more rapidly and may render tissues more easily stained by certain histological dyes. Tissues can be left in some fixatives (e.g., buffered neutralized formalin) for several months; with other fixatives (e.g., Bouin's), tissues must be transferred to alcohol immediately after fixing. Three of the more widely used fixatives are described here. For more information on fixatives and histological methods, Nagorsen and Peterson recommend Luna (1968).

Formalin (= formaldehyde solution):
Commercially available formalin solution is usually a 37 % or 40 % (weight / volume) solution. It may be best to take this full strength solution to the field to reduce volume and to dilute it before use; in this case the full strength solution is treated as 100 %, which means that for production of a 10 % solution one part of 40 % formalin solution must be mixed with 9 parts water. Formalin solution is usually acidic (pH 3 to 4.6) and tends to decalcify teeth and to excessively harden tissue. Therefore, it is best to buffer it to pH 7.0 (neutral) (Nagorsen, Peterson 1980).

10 % buffered formalin (from Nagorsen, Peterson 1980, Munson 2000)
For 1 litre:
    100 ml formalin (38-40 % formaldehyde)
    900 ml distilled water
    Buffer added:

      Buffer mixture for precise buffering to neutrality (pH 7.0) (Nagorsen, Peterson 1980):
          4 g of acid or monobasic sodium phosphate monohydrate (NAH2PO4H2O)
          6.5 g of dibasic sodium phosphate anhydrate (NA2HPO4)
          This dry salt mixture can be prepared in advance and carried into the field in plastic bags.

      Another possible buffer mixture (Munson 2000):
          4.5 gm sodium phosphate (monobasic)
          3.6 g sodium hydroxide

      Mixture in cases when such buffer is not available:
          4 g sodium chloride = table salt (Munson 2000)
          a quarter of a teaspoon of borax powder or household ammonia (Nagorsen, Peterson 1980) per litre

Bouin's solution (from Nagorsen, Peterson 1980)
    Picric acid, saturated aqueous solution 750 ml
       (if not stored in an aqueous solution, picric acid is highly volatile)
    37-40% formalin 250 ml
    Glacial acetic acid 50 ml

Alcohol-formalin-acetic acid solution (AFA) (from Nagorsen, Peterson 1980)
    37-40% formalin 10 ml
    Alcohol, 80% 90 ml
    Glacial acetic acid 5 ml

Formalin-sodium acetate solution (from Nagorsen, Peterson 1980)
    37-40% formalin 100 ml
    Sodium acetate 20 g
    Tap water 900 ml

Chemicals for other purposes

Sterile buffered glycerin (50%) for transporting tissues for culture when refrigeration is not available (from Munson, 2000):
    Buffer composed of:
          A: 21 g citric acid mixed in 1000 distilled water
          B: 28.4 g anhydrous sodium phosphate in 1000 distilled water
          Buffer: mixture of 9.15 ml of A and 90.85 ml of B.
100 ml of buffer mixed with 100 ml of glycerin.
To take the mixture into the field, it can then be sterilised in small tubes.

"Easy Blood" for transporting DNA from blood cells for genetic studies when refrigeration is not available and for preserving refrigerated or frozen DNA for longer periods of time (from Munson 2002):
    1.2 g Tris HCI
    3.7 g Na2 EDTA
    2 g sodium dodecyl sulfate (SDS)
    Water added to 100 ml

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In: Loris and potto conservation database: field methods 
Last amendment: 7 November 2002


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