Medical syringe

Claim 1

A medical syringe comprising: a first hollow elongated cylinder having a first inner diameter, one end of the first cylinder being open, the opposite end of the first cylinder being closed and provided with sealed means adapted to detachably receive a hypodermic needle; a second hollow elongated cylinder having a second and larger inner diameter, one end of the second cylinder being open, the opposite end of the second cylinder having centered therein a circular port with a diameter equal to the first diameter, said cylinders being disposed end to end along a common cylindrical axis, the opposite end of the second cylinder being secured to the open end of the first cylinder with said port being coincident with the open end of the first cylinder; a sealing disc centered on said axis and being non rotatably slidable back and forth in said cylinders along said axis, said disc having a diameter equal to said first diameter and when disposed in said first cylinder engaging the inner surface thereof with a liquid tight seal, said disc having an axially aligned member having an external thread and extending toward said second cylinder; a bushing disposed in the open end of the second cylinder and having a circular opening centered on said axis, said opening having a third diameter smaller than said first diameter, and an elongated cylindrical piston extending slidably through said opening, there being a liquid tight seal between said piston and said bushing, one end of said piston being disposed outside of the second cylinder and being enlarged, said piston being aligned with and centered on said axis, the length of the piston being longer than the combined lengths of said first and second cylinders, the other end of said cylinder having an axially disposed internally threaded bore which is engagable with said member when the piston is rotated in one direction about said axis and is disengagable from said member when the piston is rotated in opposite direction.