A device for the counterflow treatment of fibrous deformable particles with liquid in stages in a tower. In the tower the particles and liquid flow downward by small movements and the liquid flows upwardly. Each of these successive two movements constitute one stage. The ascent of liquid alone, or filtration in each stage, is produced by introductions of water with adequate pressure through the bottom of the tower. The descent of the mass of particles and liquid or mass movement in each stage, is produced by rapid removal of mass from the lower part of the tower. During filtration periods, the particles suffer only small relative displacements among them, because the upper layer of the particles is retained by a screen, that only permits the flow of liquors; in addition, successive grids extending from the proximity of the screen to the proximity of the bottom of the tower, offer resistance to movement of the particles. In order to produce both adequate mass-movement and filtration, it is necessary that the velocity of liquid in both directions be correctly determined. The velocity of descent must be sufficient to provoke the dragging, and shearing against the grids of the mass of particles. The velocity of ascent must be slow enough to produce only small local differences in particle concentration, with slight increases in concentration below the screen and the lower edges of the grids. The water introduced at the bottom of the tower, the removal of mass at the bottom of the tower, as well as the introduction of the particles are automatically controlled.