<p>A biological disk (10) has a shaft (22) on which are radially arranged a plurality of circular disks (12) composed of individual sector-shaped disks (14) having the same radius and retained by tie rods (20) with parallel axes which extend through radial stays (18). These disks (12) are maintained at a defined axial distance from each other by intermediate spacers (16). Axially adjacent spacers (16) form gaps engaged by the individual sector-shaped disks (14). The sector-shaped disks (14) are held by positive engagement between two axially adjacent spacers (16).</p>
