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:Lysozyme has a direct bacteriolytic action because it hydrolyses b-(1,4)glycosidic bonds, which are common in peptidoglycan of bacterial cell walls (Strominger and Tipper, 1974; Jolles and Jolles, 1984).
Category: