A hand-held pipette with a liquid dispensing knob at one end operably connected therewithin to a piston and piston cylinder assembly at the opposite end that is detachable from the pipette body for cleaning or replacement. An internal pawl and rack mechanism causes the piston to advance a small amount...http://www.google.co.uk/patents/US4099548?utm_source=gb-gplus-sharePatent US4099548 - Hand-held pipette for repetitively dispensing precise volumes of liquid
