NEEDLE RETRACTING MECHANISM, NEEDLE HOLDER AND HYPODERMIC SYRINGE

1. A needle retracting mechanism (1) for a hypodermic syringe (2), comprising a body (3) with a needle retraction chamber (4), which body (3) in a first end (5) is adapted to receive injectant from a syringe barrel (7) and in a second end (6) slidingly supports a needle (27) which by means of a force from a pretensioned actuator (8) is retractable into the needle retraction chamber (4), the actuator (8) being releasable by response to the injectant, characterized in comprising a funnel-shaped entrance opening (18) to the needle retraction chamber (4), a retainer (9) for the actuator (8) and the needle (27), the retainer (9) comprises a compressible portion (10) which in a retaining position is bigger than the entrance opening (18) and abuts funnel-shaped sides (16) of the entrance opening (18), and in a compressed release position is smaller than the entrance opening (18) and can enter the needle retraction chamber (4) together with the needle (27), the pretensioned actuator (8) forces the retainer (9) into the funnel-shaped entrance opening (18), forcing the compressible portion (10) towards the release position, a spacer (11) for keeping the compressible portion (10) in the retaining position, made from a material which after some time in contact with the injectant loses its mechanical strength, whereupon a contact between the spacer (11) and the injectant causes the spacer (11) to lose its mechanical strength, the actuator (8) forces the compressible portion (10) into the release position and into the entrance opening (18), causing the retainer (9) and needle (27) to enter the needle retraction chamber (4). 2. A needle retracting mechanism (1) according to claim 1, characterized in that the compressible portion (10) of the retainer (9) comprises elastic arms (12) which in first ends (13) are integral with a base portion (15) of the retainer (9) and in second ends (14) are moveable between the retaining position and the release position. 3. A needle retracting mechanism (1) according to claim 2, characterized in that the second ends (14) of the elastic arms (12) have oblique end faces (17), corresponding to the funnel-shaped sides (16) of the entrance opening (18). 4. A needle retracting mechanism (1) according to claim 2 or 3, characterized in that the elastic arms (12) have mountings (29) for the spacer (11). 5. A needle retracting mechanism (1) according to any of the claims 2 to 4, characterized by two arms (12) and a spacer (11) formed by a bolt (11