Apparatus for detecting light-scatter from small particles irradiated by a light beam comprising: (a) an optically transparent flow cell having a cell-interrogation zone through which particles can be made to pass, one at a time, while a beam of optical radiation irradiates each particle, said flow cell having an optically transparent wall through which light scattered from irradiated particles can pass; (b) a plurality of elongated optical fibers (33, 34, 35, 36, 37, 38), each operating to receive light at a light-collecting end thereof and to transmit such light, via multiple internal reflections, to an opposing light-discharge end at which the transmitted light is discharged, each of said optical fibers having a central optical axis extending longitudinally through said optical fibers; (c) at least one photodetector (PD1-PD6) positioned adjacent the respective light-discharge ends of said optical fibers to receive and detect discharged light; and (d) an optical fiber holder; the apparatus characterised by the optical fiber holder comprising: (i) a forward light-scatter collecting component for supporting a portion of each optical fiber (33, 34, 37, 38) in the vicinity of its respective light-collecting end so that the light-collecting ends are positioned to collect forwardly scattered light and the respective optical axes of the supported fiber portions converge toward the apparent position of particles irradiated within said interrogation zone; wherein the forward light-scatter collecting component comprises a central elongated bore hole; (ii) an axial light collecting component for supporting additional optical fibers (35, 36) in positions to collect axial beam light as modulated in intensity by particles passing through the beam path, the axial light collecting component comprising: a centrally located opening; and a light-diffusing surface for diffusing said axial beam light prior to being collected by said additional optical fibers (35, 36); wherein the central elongated bore hole and centrally located opening are positioned to transmit axial beam light to said light-diffusing surface, said central elongated bore hole being of a length and diameter to restrict the passage of diffused axial light back towards said flow cell. (a) an optically transparent flow cell having a cell-interrogation zone through which particles can be made to pass, one at a time, while a beam of optical radiation irradiates each particle, said flow cell having an optically transparent wall through which light scattered from irradiated particles can pass; (b) a plurality of elongated optical fibers (33, 34, 35, 36, 37, 38), each operating to receive light at a light-collecting end thereof and to transmit such light, via multiple internal reflections, to an opposing light-discharge end at which the transmitted light is discharged, each of said optical fibers having a central optical axis extending longitudinally through said optical fibers; (c) at least one photodetector (PD1-PD6) positioned adjacent the respective light-discharge ends of said optical fibers to receive and detect discharged light; and (d) an optical fiber holder; the apparatus characterised by the optical fiber holder comprising: (i) a forward light-scatter collecting component for supporting a portion of each optical fiber (33, 34, 37, 38) in the vicinity of its respective light-collecting end so that the light-collecting ends are positioned to collect forwardly scattered light and the respective optical axes of the supported fiber portions converge toward the apparent position of particles irradiated within said interrogation zone; wherein the forward light-scatter collecting component comprises a central elongated bore hole; (ii) an axial light collecting component for supporting additional optical fibers (35, 36) in positions to collect axial beam light as modulated in intensity by particles passing through the beam path, the axial light collecting component comprising: a centrally located opening; and a light-diffusing surface for diffusing said axial beam light prior to being collected by said additional optical fibers (35, 36); (i) a forward light-scatter collecting component for supporting a portion of each optical fiber (33, 34, 37, 38) in the vicinity of its respective light-collecting end so that the light-collecting ends are positioned to collect forwardly scattered light and the respective optical axes of the supported fiber portions converge toward the apparent position of particles irradiated within said interrogation zone; wherein the forward light-scatter collecting component comprises a central elongated bore hole; (ii) an axial light collecting component for supporting additional optical fibers (35, 36) in positions to collect axial beam light as modulated in intensity by particles passing through the beam path, the axial light collecting component comprising: a centrally located opening; and a light-diffusing surface for diffusing said axial beam light prior to being collected by said additional optical fibers (35, 36); a centrally located opening; and a light-diffusing surface for diffusing said axial beam light prior to being collected by said additional optical fibers (35, 36);