Hypodermic syringe

Abstract

A hypodermic syringe has a generally cylindrically tubular body extending along an axis and having an axial front end formed with a radially outwardly projecting annular bead, a piston axially displaceable in the body, a plug having a rearwardly directed flange fitting complementarily over the front end of the body at the bead and forwardly blocking the body, and a flat soft seal ring compressed axially between the plug and the front end of the body. The body has a rear end provided with a finger-rest crosspiece and the piston is provided with a plunger projecting axially out the rear end past the crosspiece.

I claim: 
     
       1. A hypodermic syringe comprising: a generally cylindrically tubular body extending along an axis and having an axial front end formed with a radially outwardly projecting annular bead, the body having a rear end provided with a finger-rest crosspiece;   a piston axially displaceable in the body and provided with a plunger projecting axially out the rear end past the crosspiece, the crosspiece being internally threaded and the plunger having a complementarily externally threaded front portion threadedly engageable in the crosspiece and a small-diameter rear portion slidable axially through the crosspiece;   a plug having a rearwardly directed flange fitting complementarily over the front end of the body at the bead and forwardly blocking the body; and   a flat soft seal ring compressed axially between the plug and the front end of the body.   
     
     
       2. The syringe defined in claim 1, further comprising: a needle secured adhesively into the plug and having a rear end and a front end, the seal ring being formed with a central opening fitting around the rear needle end, the plug being formed with a radially outwardly projected securing rim; and   a needle protector fitted over the needle and snugly engaged around the rim.   
     
     
       3. The syringe defined in claim 2 wherein the needle protector is made of a hard plastic and is provided with a soft seal body into which a front end of the needle is poked. 
     
     
       4. The syringe defined in claim 1 wherein the seal ring is formed with a central opening fitting snugly around the pin of the tip cap. 
     
     
       5. The syringe defined in claim 1 wherein the plug has a forwardly projecting collar adapted to fit with a separate needle assembly. 
     
     
       6. The syringe defined in claim 1, further comprising a partition plug axially slidable in the body between the piston and the front body end and forming in the body a rear compartment adapted to hold a solvent and a front compartment adapted to hold a dissolvable medicament, the body being formed generally centrally with an inwardly open bypass groove, the flange of the plug being formed with at least one radially throughgoing orifice, the plug being displaceable between a front position with the orifice forward of the body front end and thereby venting the front compartment and a rear position with the orifice backward of the body front end and blocked by the body.   
     
     
       7. A hypodermic syringe comprising: a generally cylindrically tubular body extending along an axis and having an axial front end formed with a radially outwardly projecting annular bead;   a piston axially displaceable in the body;   a plug having a rearwardly directed flange fitting complementarily over the front end of the body at the bead and forwardly blocking the body;   a flat soft seal ring compressed axially between the plug and the front end of the body; and   a protective cap made of a hard but frangible material covering the plug and formed with a rear end fixed permanently to the plug,   a front end fitting over and covering the plug,   a pin projecting axially backward from the front end through the plug, and   a weakened region joining the protective-cap front and rear ends.     
     
     
       8. The syringe defined in claim 7 wherein the body has a rear end provided with a finger-rest crosspiece and the piston is provided with a plunger projecting axially out the rear end past the crosspiece. .Iadd. 
     
     
       9.  A hypodermic syringe comprising: a tubular body extending along and centered on an axis and having an axial front end having an outer surface;   an end piece on the front end of the body;   a deformable seal fixed on the end piece, fittable sealingly against the front end and adapted to receive a needle;   mounting formations extending axially back from the end piece and having an inner surface radially confronting the outer surface of the front end of the body., one of the surfaces being formed with a front groove open radially toward the other surface and, axially spaced backward therefrom, with a rear groove radially toward the other surface, the other surface being formed with a ridge engageable in a front position of the end piece radially inward into the front groove and in a rear position of the end piece radially inward into the rear groove, the formations being of such an axial length that the seal is fitted snugly against the front end in the rear position and blocks flow out of the body through the front end but is not snugly fitted against the front end in the front position and forms therewith a gap permitting flow out of the body through the front end; and   a piston axially displaceable in the body. .Iaddend. .Iadd.     
     
     
       10.  The hypodermic syringe defined in claim 10 wherein the grooves are formed on the end piece and the ridge on the body. .Iaddend. .Iadd.11. The hypodermic syringe defined in claim 9 wherein the end piece is formed with a forwardly projecting and axially centered tubular extension and with an axially throughgoing passage, the seal having a forward extension fitting complementarily in the end-piece extension, the syringe further comprising a tip cap fitted over the end-piece extension and blocking a front end of the passage. .Iaddend. .Iadd.12. The hypodermic syringe defined in claim 9, further comprising   a protector ring axially slidable on the end piece between a front position mounted thereon forward of the formations and a rear position engaged around the formations and holding same in the rear position of the end piece in the rear groove against radial outward deflection therefrom.   
     
     
        .Iaddend. .Iadd.13.  The hypodermic syringe defined in claim 12 wherein the protector rinq is unitarily formed with a protector cap and is connected to it via a weakened-line region permitting the cap to be snapped off the ring. .Iaddend.