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:Group 3: mice were anesthetized in a Plexiglas chamber with 3% isoflurane in air for 25 min (after the desired concentration was reached) twice daily, as described previously (12); 0.
Category: