Vehicles for Fixatives

Ideally, the solution in which the fixative is dissloved and administered should simulate as close as possible, the tissue fluids which form the natural environment of the cells of the specimen.

1. pH- A buffer system that maintains physiological pH (7.2-7.4- mammalian systems) should be used to prevent drastic lowering of tissue pH.

2. Osmolarity - The total osmolarity of the fixing solution should be isosmotic with tissue fluids in order to prevent shrinkage or swelling of cells.

In practice, slightly hypersosmotic solution often gives the best practical results since crosslinking effectively removes proteins from solution as well as the glutaraldehyde molecules which link them.

3. Ionic Environment - Ions such as Ca++, Mg++, Na+, Cl- should be present at concentrations which simulate tissue fluids in order to prevent macro-molecular denaturation.

4. Fixative Concentration - Normally a 2% solution of glutaraldehyde in an appropriate buffer is ideal, although more dilute solutions (1% or less) may be necessary in order to preserve enzyme and antigenic activity of proteins.