a low cost , easy to use , snap - on , linear - to - vernier syringe by which a volume of material may be controllably and accurately delivered to a recipient . by virtue of the present invention , a piston supporting collar member may be securely snapped into releaseable engagement with a conventional , disposable syringe cylinder to complete the syringe assembly . moreover , the conventional syringe cylinder is thereby converted into a precisely accurate pipetting cylinder to control the infusion of highly potent , dosage sensitive , radioactive , or expensive drugs , and the like , without requiring any modification to the cylinder . the syringe assembly is particularly adapted to permit rapid switching between freely rotated and incrementally rotated modes of operation , whereby a predetermined volume of material may be selectively imparted from the syringe cylinder , either continuously or in discrete and precisely calibrated increments .