Syringe with needle retraction arrangement

A syringe, comprising:

• a hollow barrel having an open end portion, a needle mounting portion, and a tubular needle hub extending from said needle mounting portion to provide a needle passageway therethrough and an end shoulder radically extended inwardly from a free end of said needle mounting portion;
• a hollow needle having a tissue penetrating end and a tip end thereof affixed with a cylindrical tip head which has a shallow ring groove provided thereon, wherein said tip head of said hollow needle is disposed in said needle mounting portion with said tissue penetrating end penetrating through said needle passageway;
• a compression spring surrounding said hollow needle and having two ends pressing against said end shoulder of said needle hub and said tip head of said hollow needle respectively;
• an O-ring removably resting around said ring groove of said tip head;
• a mounting seat, which is integrally affixed within said needle mounting portion, having an O-ring passage coaxially aligned with said needle passageway of said needle hub, a top end portion of said O-ring passage reducing diameter to form a stopper shoulder against which said O-ring abuts, wherein a circular gap is formed between said ring groove of said tip head of said hollow needle and an annular wall of said O-ring passage, said circular gap having a width smaller than a diameter of said O-ring so as to compress said O-ring between said stopper shoulder and said ring groove and to securely mount said tip head in said O-ring passage;
• and
• a hollow plunger adapted to travel through said hollow barrel, said hollow plunger having an outer close end and an inner end inserted in said hollow barrel through said open end portion, a closure seat being connected to said inner end of said hollow plunger so as to define a receiving cavity inside said hollow plunger, said closure seat having an entrance aperture positioned above said O-ring passage of said mounting seat, said entrance aperture being covered by a pusher member which is circumferentially connected with said entrance aperture in such a manner that said pusher member is detached to open said entrance aperture when a predetermined pound of urging force is applied to said pusher member;
• thereby, when said closure seat of hollow plunger is intentionally pushed towards said mounting seat, said pusher member presses said tip head as well as said O-ring thereon to slide towards said needle hub and further compress said compression spring to store a resilient force, moreover when said O-ring is pressed to travel through of said O-ring passage, said resilient force of said compression spring increases to a force larger than said predetermined pound of urging force, so that the engagement of said O-ring between said ring groove of said tip head and said annular wall of said O-ring passage is released, and said resilient force stored in said compression spring upwardly pushes said tip head of said hollow needle to press against said pusher member until said entrance aperture is opened, so that said hollow needle, said pusher member and said compression spring are retracted into said receiving cavity of said hollow plunger.