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:Previous studies of the chronic intoxication with cylindrospermopsin [41] or MCs have shown proliferation of connective tissue and dilatation of tubules and glomeruli [19,29] filled with proteinaceous material.
Category: