A hypodermic syringe includes a barrel with a plunger assembly slidably extending therein. The plunger assembly includes an outer plunger and an inner plunger telescoping together with a bungee resisting extension of the assembly. The inner and outer plungers may be locked in the extended position with...http://www.google.se/patents/US20030045838?utm_source=gb-gplus-sharePatent US20030045838 - Retractable hypodermic syringe
