Abstract: The present invention relates to a pressure injection mechanism of the type which, when triggered, expresses predetermined dosages of liquid under high pressure from a dosage orifice at speeds enabling the same to penetrate an injection site which may be the skin of a human or an animal, the stalk or other surface of a plant and so forth. The apparatus is characterized by a novel triggering mechanism which assures that the apparatus may be triggered to effect a dosage administering cycle only when the dosage orifice is positioned against the injection site with a predetermined orientation.