Abstract: An improved hypodermic syringe having a cannula retractable within the syringe barrel after injection. A piston in reciprocable sealing engagement with the interior of the syringe barrel includes an engaging structure at its forward end which is attachable to the cannula base. After administration of the fluid contained within the syringe chamber, the piston engages the cannula base, preferably by "snapping" on to the rearward end of the cannula, and retracts the cannula within the barrel. The barrel may additionally be designed so as to prevent complete removal of the piston. In an alternative embodiment, a cannula retracting mechanism is provided in a hypodermic syringe assembly for drawing blood.

Abstract: A syringe having a barrel and a piston actuated plunger reciprocable therein includes a means for retracting the cannula subsequent to dispensing fluid from the syringe. The plunger is engageable with the forward end wall of the syringe barrel after the fluid is dispensed so that retraction of the plunger causes the end wall to break away from the barrel and retract the cannula attached thereto entirely within the barrel. In this manner, accidental puncture and contamination by the cannula is avoided. A plurality of serrations on the forward end wall and adjacent its juncture with the syringe barrel allows the forward end wall to be broken away after mating surfaces on the forward end wall and the plunger rod are engaged. In a first embodiment, the mating surfaces are threaded so that rotation of the plunger rod is required for engagement. In a second embodiment, rotation is not required since the mating surfaces are in the form of a snap-in annular rib and groove.