Pipette means

Claim 1

Pipette means having aspirating and expelling means and a substantially cylindrical tube connected to a pipette tip for fluid flow therebetween; the expelling means being arranged to apply pressure to the outer surface of the cylindrical tube, the diameter and wall thickness of which being chosen so that said tube is compressed elastically and substantially uniformly and circumferentially to reduce the internal volume thereof, tending to expel any liquid from the pipette tip; and the aspirating means being arranged to relieve pressure from the outer surface of said tube, allowing the tube to expand substantially circumferentially and uniformly so that liquid may thereby be drawn into the pipette tip; the said expelling and aspirating means operating the application and relief respectively of fluid pressure to and from the cylindrical tube; said pipette means also having means for diluting a sample including diluent valve means for permitting a controlled amount of liquid diluent to pass through the cylindrical tube to the pipette tip to dilute a sample when the expelling means applies pressure to the cylindrical tube and wherein the source of fluid pressure is the source of liquid diluent arranged as a head tank at a level about the cylindrical tube great enough to provide pressure adequately to compress the cylindrical tube.