Abstract: A syringe having a sheath that is slidingly received on a barrel of the syringe so as to be movable between a retracted needle exposing position and an extended needle surrounding position. A boss fixedly attached to the syringe barrel cooperates with an L-shaped bayonet slot in the sheath to guide the cylindrical sheath. The sheath is connected to the syringe by a coil spring which biasingly urges the sheath into the extended needle surrounding position. The sheath is connected to the coil spring such that as the sheath is advanced from the retracted position to the extended position, the spring biasingly rotates the sheath with respect to the barrel such that the boss is advanced into a laterally extending portion of the slot so as to prevent accidental compression of the sheath. When the sheath is advanced to the retracted position a barb on the barrel cooperates with a barb receiving aperture in the sheath to restrain the sheath in the retracted position.