Fig. 1.

Different types of cages used for voiding spot assay and representative images of voided filter papers. A: standard cage used for daily mouse housing in animal facility. B: custom-built new rectangular cage with sharp cage corners and edges, which differs from the standard cage. C: traditional Techniplast metabolic cage with metal grid floor; filter paper can be placed either above the grid or below the grid, in which case mice will walk on the grid. D: representative image of voided filter paper from a standard cage. E: representative image of voided filter paper from a new rectangular cage. F: representative image of voided filter paper from a metabolic cage. The quarter dollar coin at bottom right of D (surface area of 462 mm²) serves as the size standard.