158 preferably the suspension fluid and the sheath fluid flow through passage 178 in laminar flow i e in substantially non mixing layers respectively of the suspension fluid and the sheath fluid such laminar flow helps the beads to flow through passage 178 along a substantially straight path the sheath fluid also helps to even out the flow of beads and assists in achieving suitable serial separation of beads the sheath flow may be controlled to optimize the flow of beads through passage 178 various modifications can be made to the apparatus and process described for example by incorporating an electronic counter in the control unit it is possible to count electrical peaks and disable the syringe actuator only after a predetermined number of peaks is counted in this way if desired a preselected number of beads can be deposited in each well the control system can be programmed to cause the beads in the pipette to be flushed into the waste collector if the number of beads passing through the aperture into the pipette exceeds the preselected number the pipette with its aperture 54 can be readily removed for cleaning or for replacement by another pipette having a different aperture it is possible to eliminate the jewel 52 altogether and thereby avoid the potential problems resulting from detachment of the jewel from the pipette this can be done by forming the aperture directly in the wall of the pipette provided that the wall thickness is sufficiently small in still another modification of the apparatus openings are provided at the bottoms of the wells in the well plates and filters are situated in the openings.