Abstract: A single barrel two compartment assembly for medicaments comprising an elongated cylindrical hollow barrel having a normally sealed discharge end, a bypass plunger made of a pliable resilient material having a forward section of a diameter slightly greater than the diameter of the barrel, means defining a seat in the bypass plunger, a plunger rod having a tip engageable in said seat for actuating said bypass plunger axially in said barrel and seal means for sealing the open end of the said barrel remote from said discharge end, said bypass plunger normally dividing said barrel into a first compartment to one side of the bypass plunger for a powder medicament and a diluent compartment on the opposite side of said bypass plunger, actuation of said bypass plunger in one direction creating internal diluent pressure whereby said diluent bypasses the periphery of said plunger to mix with said powder medicament.

Abstract: A plunger rod and piston for a syringe which are easily and quickly assembled with a minimum force. The plunger rod has a tip of truncated "christmas tree" shape and the piston, which is of a flexible resilient material, has a pocket of complementary shape to receive the plunger tip. The tip includes a series of frusto conical segments of decreasing cross-wise dimension from the base to the terminal end of the tip thereby defining a plurality of circumferentially extending, axially spaced radially directed shoulders.The piston pocket has a series of frusto conical pocket sections decreasing in size from the open end thereof to define a plurality of circumferentially extending axially spaced, radially directed, flexible lips. Upon assembly of the tip in the piston pocket, the lips deflect to permit seating of the tip therein and then engage behind the radial shoulders to lock the parts together.