A self dispensing reagent cartridge includes a vessel with a movable piston at one end and a puncturable self sealing septum at an opposite end. A hollow needle is located in alignment with the septum. The vessel is moved toward the needle to enable the needle to puncture the septum. The piston is then moved toward the septum to enable a predetermined amount of liquid in the vessel to be transferred outwardly of the vessel through the needle in an amount corresponding to the piston stroke.