| 摘要 |
A hypodermic syringe comprises a housing ( 1 ), which includes a barrel portion ( 1.4 ) and an injectant chamber ( 1.5 ), where the injectant chamber has a smaller cross-sectional area than the barrel portion ( 1.4 ). A plunger ( 2 ), which comprises a piston ( 3 ), is slideably mounted within the barrel portion ( 1.4 ) and extends into the injectant chamber ( 1.5 ). A retractable needle assembly ( 5 ) is provided, together with stored energy means ( 4 ), so that, at the completion of an injection stroke, the piston ( 3 ) becomes attached to the needle assembly ( 5 ) and the stored energy is released to retract the needle assembly ( 5 ) into the housing ( 1 ). Co-operating features ( 3.7, 5.7 ) may be arranged on the piston ( 3 ) and needle assembly ( 5 ) so that complete evacuation of the injectant chamber ( 1.5 ) is not impeded. As the parameters of the stored energy means ( 4 ) are not limited by the physical dimensions of the injectant chamber ( 1.5 ), this arrangement is particularly suitable for small capacity syringes, i.e. 3 ml or less.
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