Abstract: An apparatus for injecting a substance into a human or animal comprising a body adapted to have the substance to be injected pass therethrough, a needle mounted on the body and a needle guard mounted on the body between an extended position in which the guard obstructs access to the point of the needle and a retracted position in which the guard does not materially obstruct access to the point of the needle. The guard is releasably retained in the retracted position, and interlocking members on the body and the guard are responsive to generally axial movement of the guard to the extended position for interlocking to substantially prevent movement of the guard back toward the retracted position.

Abstract: A hypodermic syringe comprising a barrel, a needle coupled to the barrel and terminating in a point and a needle guard mounted on the barrel for movement between an extended position in which the guard shields the needle and a retracted position in which the guard does not shield the needle. The guard can be releasably locked in the retracted position and locked in the extended position. Locking of the guard is accomplished by a track on the internal surface of the guard and track-engaging members on the barrel.