Abstract: A disposable hypodermic syringe having a needle cannula fixed to a piston assembly. The piston assembly is held within the elongated hollow barrel of said hypodermic syringe by a compressed spring and a trigger. When said trigger is disengaged with said piston assembly said spring pushes said piston assembly and said needle cannula into said barrel of said hypodermic syringe and holds said needle cannula fixed to said piston assembly within said barrel and is further prevented from being pushed out of said elongated hollow barrel by a rim in said elongated hollow barrel thus preventing any accidental injection of bacteria, virus or other undesirable material into others. The disengagement of said trigger with said piston assembly is accomplished with only one and the same hand that is used to inject the needle cannula and medicament into a body.