An injector comprising an outer housing, a generally longitudinally extending keyway formed in the outer housing, an inner housing located interiorly of the outer housing, a guide member mounted at one end of the inner housing, the guide member having at least one protrusion adapted to engage the keyway, a spring member, the spring member having a first end abutting the outer housing, a second end of the spring member abutting the guide member, a syringe mounted interiorly of the inner housing, a needle mounted on one end of the syringe, the syringe having a plunger and a plunger rod, a finger rest member mounted over the outer housing, the finger rest member being opaque to thereby prevent visual access to the keyway.
