Non-reusable syringe

Claim 1

A non-reusable syringe comprising: a hollow syringe body having a first end to which the cannula is to be attached and a second end, a piston for insertion into the body second end and for travel within said body, the piston having a longitudinally extending stem with a pair of spaced apart radially extending ribs, each of said ribs having on its outer edge a ratchet tooth profile, the profile of the teeth on each rib extending in the opposite direction, means within the body forming a pair of slots at a position corresponding to the pair of spaced ribs of the stem, one of said slots having a stop means for engaging the teeth of a rib profile and the other slot permitting free passage of the rib profile, movement of the piston in a direction from the first end toward the second end of the body to a predetermined first position being permitted with the teeth of the profile of one rib passing over the stop, and means within the body cooperating with the stem in said first position permitting rotation of the stem to change the positions of the ribs relative to their locations in the slots, movement of the piston from the predetermined first position toward the body first end permitted with the teeth of the profile of the other rib passing over the stop, and retraction of the piston from the body first end toward the second end prevented by the teeth of the profile of said other rib engaging the stop within the body.