Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…to Reduction in Cell Length and Change in Cell
07.07.004
For thin section transmission electron microscopy, the proventriculus was placed directly in 2.5% glutaraldehyde, 2% paraformaldehyde and 0.1% picric acid in 100 mM phosphate (pH 7.2) and processed as described previously (Dawe et al. 2005).
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