Flow cell for particle scanner

A flow cell having a body defining a passage through which a fiber-containing fluid can be caused to flow in a first direction, said body having two opposite walls defining sides of said passage, said walls being parallel to each other and transparent to radiation whereby fibers in said fluid can be illuminated and viewed by radiation travelling in a second direction through said walls and said fluid, each of said walls lying in a first plane, said passage being further defined by a pair of opposite diverging flat surfaces each lying in a second plane, said first planes being at right angles to said second planes, said second planes being parallel to said second direction of said radiation and being at an angle to said first direction of said fluid flow thereby forming a tapered passage having a first smaller end and a second larger end, said passage having a width which increases uniformly and progressively from said first end to said second end, said passage having an inlet at said first end and an outlet at said second end, said flow of fluid in said tapered passage acting to produce a couple which rotates ends of said fibers towards said diverging flat surfaces of said passage and thus rotates said fibers to a larger angle to said direction of flow.