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:5 mm 24 mm), fixed with 4% paraformaldehyde for 10 min, permeabilized with 20 mM NaOH for 45 s (Iwatani et al., 2005), and washed twice with PBS.
Category: