In a preferred embodiment, a tubular syringe had a separate terminal plunger portion positioned to be pushed into a position of blocking flow to and from the needle passage as the plunger proximal portion is moved inwardly to expel syringe contents, and at the blocking position a male member being locked into a female member positioned to permit movement to the blocking position but preventing withdrawal of the terminal portion from the blocking position, preventing subsequent intake or outflow through the syringe needle passage.