. "Further objects, features, and advantages will appear from the following detailed description with reference to the drawings, in which: FIG. 1 is a longitudinal section of a hypodermic syringe in accordance with the invention, FIG. 2 shows on a larger scale a modified form of operating valve for a syringe in accordance with the invention, FIG. 3 is a schematic longitudinal section of a second form" . . . .