Non-refillable multiple dosage syringe

Claim 1

In a multiple dosage syringe that automatically signals to the user's sense of feel when a dose of predetermined volume has been discharged therefrom, including: an elongate hollow barrel capable of holding a charge comprising a plurality of such doses of a liquid material; discharge means mounted on the forward end of said barrel through which each of said doses can be discharged from said barrel; a piston slidably mounted within said barrel; an elongate piston member having a central axis, affixed to said piston and extending rearwardly through the rear end of said barrel; and stop means operatively associated with said barrel and member that tend to restrict forward movement of said piston after a dose of said liquid material is discharged through said discharge means, and stop means comprising a plurality of longitudinally spaced stops formed on the periphery of said elongate piston member, each of said stops having a greater longitudinal dimension than its transverse thickness dimension and each stop protruding outwardly from the periphery of the elongate member to such an extent that it will strike a member at the rear end of said barrel when said piston member is moved forwardly, each of said stops being sufficiently removable from its outwardly projecting position to permit said piston member and piston to move further forward within said barrel toward said discharge member; the improvement comprising: a longitudinal undercut providing a line of maximum weakness of each stop extending in a longitudinal plane obliquely outward in the rearward direction relative to the central axis of the elongate member so that the portion of the stop outside said line can be broken off, leaving an inner portion of the stop protruding somewhat outside the elongate member, the amount of the protrusion of said inner portion being sufficiently slight so that the protrusion can move through the barrel in the direction, the rear end of the protrusion having an edge which scores the inner wall of the barrel during movement of the piston member sufficiently to prevent a sufficient seal between the piston and the barrel wall to permit discharging accurate quantitative doses from a fresh charge of liquid material after the original charge has been discharged.