A sheath is provided as a cover over a hollow needle for use by medical personnel in combination with a syringe. When needle is not in use, the sheath protects medical personnel from accidental scraping or injections. During use in injections, the sheath is retracted by skin contact into a chamber attached...http://www.google.es/patents/US4850996?utm_source=gb-gplus-sharePatente US4850996 - Safety needle
