The present invention relates to a hematology instrument system that discriminates platelets from red blood cells, debris and other particles within a blood sample. The track assembly also includes two drive gears disposed externally to the track and configured to frictionally engaged an outer surface of a corresponding one of the tires. A valve is inserted within one of the walls at the first half of the pouch. The field may thus be an electric field or a magnetic filed. The illuminated product web can be observed through this observation slit by means of a line camera.