A needle-syringe assembly, operable in a normal mode and convertible to a retraction mode, comprises an elongated, generally cylindrical barrel, a plunger slidably mounted in the barrel, and a needle holder carrying a hollow needle on the distal end thereof. The barrel forms a hollow nozzle located at...http://www.google.es/patents/US5514100?utm_source=gb-gplus-sharePatente US5514100 - Hypodermic needle assembly
