| 摘要 |
A piston in a syringe barrel has a cavity that opens toward the distal end of the barrel. A needle assembly has a hub, a hollow needle fixed in the hub, and a spring seated between the distal end of the barrel and the hub. A membrane is between the hub and the opening of the piston. A locking member is lodged between the barrel and the needle assembly, holding the needle assembly within the barrel to compress the spring. The piston is displaceable through functional positions in which the piston (a) forces serum out through the needle, (b) urges the membrane against the hub, and (c) dislodges the locking member thereby releasing the needle assembly such that the spring displaces the hub and at least a portion of the membrane into the cavity and withdraws the needle tip into the distal end of the barrel.
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