Hypodermic syringe with retractable needle

A hypodermic syringe comprising:

• a barrel having a closed end, an open end, and an interior surface;
• a plunger reciprocally received in said barrel through said open end in sealing engagement with said interior surface of said barrel and forming a chamber;
• a hollow needle detachably attached to said barrel at said closed end thereof providing communication between said chamber and the exterior of said barrel and wherethrough liquid in said chamber may be injected;
• means for forming a hole in said plunger for receiving said needle therethrough;
• cavity means in said plunger and communicating with said hole for receiving said needle therein when detached from said barrel;
• biasing means connected to said plunger for drawing said needle through said plunger hole and into said cavity means when said needle is detached from said barrel;
• attachment means connected to said biasing means and located between said biasing means and said needle for attaching said biasing means to said needle when said plunger approaches said barrel closed end;
• and,
• wherein said needle is detached from said barrel by a predetermined substantially longitudinal force.

A hypodermic syringe comprising:

• a barrel having a closed end, an open end, and an interior surface;
• a plunger reciprocally received in said barrel through said open end in sealing engagement with said interior surface of said barrel and forming a chamber;
• a hollow needle detachably attached to said barrel at said closed end thereof providing communication between said chamber and the exterior of said barrel and wherethrough liquid in said chamber may be injected;
• means for forming a hole in said plunger for receiving said needle therethrough;
• biasing means connected to said plunger and attachable to said needle for drawing said needle through said plunger hole when said needle is detached from said barrel;
• attachment means between said biasing means and said needle for attaching said biasing means to said needle when said plunger approaches said barrel closed end;
• wherein said attachment means includes a first mating member connected to said biasing means and a second mating member connected to said needle and wherein said first and second mating members attach to one another when said plunger approaches said barrel closed end;
• cavity means in said plunger and communicating with said hole for receiving said needle therein when detached from said barrel;
• wherein said biasing means is substantially in said cavity means;
• and,
• wherein said first mating means is detachably attached to said plunger and detaches from said plunger by a predetermined substantially longitudinal force.

A hypodermic syringe comprising:

• a barrel having a closed end, an open end, and an interior surface;
• a plunger reciprocally received in said barrel through said open end in sealing engagement with said interior surface of said barrel and forming a chamber;
• a hollow needle detachably attached to said barrel at said closed end thereof providing communication between said chamber and the exterior of said barrel and wherethrough liquid in said chamber may be injected;
• means for forming a hole in said plunger for receiving said needle therethrough;
• biasing means connected to said plunger and attachable to said needle for drawing said needle through said plunger hole when said needle is detached from said barrel;
• and,
• wherein said needle is attached to said barrel through a region of structural weakness, said needle detaching from said barrel substantially at said region of structural weakness.

A hypodermic syringe comprising:

• a barrel having a closed end, an open end, and an interior surface;
• a plunger reciprocally received in said barrel through said open end in sealing engagement with said interior surface of said barrel and forming a chamber;
• a hollow needle detachably attached to said barrel at said closed end thereof providing communication between said chamber and the exterior of said barrel and wherethrough liquid in said chamber may be injected;
• means for forming a hole in said plunger for receiving said needle therethrough;
• cavity means in said plunger and communicating with said hole for receiving said needle therein when detached from said barrel;
• biasing means connected to said plunger for drawing said needle through said plunger hole and into said cavity means when said needle is detached from said barrel;
• attachment means connected to said biasing means and located between said biasing means and said needle for attaching said biasing means to said needle when said plunger approaches said barrel closed end;
• wherein said attachment means includes a first mating member connected to said biasing means and a second mating member connected to said needle and wherein said first and second mating members attach to one another when said plunger approaches said barrel closed end;
• and,
• wherein said first mating member includes a detachably attached annular lip larger than said plunger hole and preventing said first mating member from being drawn through said plunger hole by said biasing means, said lip being detached from said first mating member by a predetermined substantially longitudinal force whereby said first mating member may be drawn through said plunger hole and into said cavity means.