The POLYESTER P 35 - Procedure
Fresh brains are fixed the usual way with 10 % formaldehyde for 4-6 weeks. Specimens which have been fixed by other methods should be avoided for this procedure, because other fixation methods may alter the P 35 reaction.
After embedding in 20 % gelatin (Barnett et al., 1980) brains are cut with a meat slicer into 4 mm slices. To prevent degredation of the slices, after cutting and during subsequent handling, they are placed on a piece of wet filter paper before being transferred to stainless steel grids. The grids containing the slices are placed into a stainless steel basket for flushing.
The basket of slices is rinsed with cold tap water overnight and cooled to 5 ° C before proceeding.
The basket of slices is placed in 100 % acetone at -20 ° C for 3 days.
The basket of brain slices is placed in a bath containing a mixture of P 35/A 9 (100 parts P 35-polymer and 2 parts A9-hardener) for one day at 5 °C. This bath might be the 2. immersion bath mixture of the previous run of specimens.
The basket of brain slices is placed in a bath containing a mixture of P 35/A 9 (100:2) for a further 24 hours at 5 °C. This bath might be the bath used for forced impregnation during the previous run of specimens.
The basket of brain slices is transferred to a fresh P 35 - A 9 mixture (100:2) and placed under vacuum for 24 hours at room temperature. The vacuum is increased until 10 - 15 mm Hg is attained.
The basket of slices is removed from the vacuum chamber. Individual slices are placed between two sheets of glass plates. Each sheet consists of an outer piece of safety glass and an inner sheet of float glass, the latter sheet facing the brain slices. A silicone gasket is placed between the outer edges of the sheets and the clamped in position using fold-back clamps. The double glass chambers, containing the specimens, are filled with a fresh P 35 - A 9 (100:2) mixture.
After casting the double glass chambers are exposed to UVA-light for 3 hours. During this procedure it is necessary to cool the chambers either by ventilators or by blowing compressed air over both sides of the double glass chamber.
Following light curing the double glass chambers are placed in a well-ventilated oven at 45 °C for 5 days.
When curing is completed the glass chambers are dismantled and the sections are trimmed on a band saw. After sawing the edges are smoothed using a belt sander.
The POLYESTER P 40 - Procedure
This technique has advantages over the others. P 40 resin has a lower viscosity than the P 35 resin. The advantages of using this technique are:
- The same polymer can be used for immersion, impregnation, and casting of specimens.
- Only single float glass chambers are necessary when casting specimens as compared with the expensive double glass chambers, containing safety glass, as in the P 35 method.
- P 40 is cured by UVA-light only, therefore, there is no requirement for an expensive ventilated heat cabinet, as in the P 35 method.
- P 40 can be used for production of transparent body slices as well as brain slices.