A syringe-carpule assembly comprising first and second carpules, a housing holding the first and second carpules in an end-to-end relationship, an outer hollow plunger rod supported by and slidable relative to the housing, and an inner hollow rod having first and second openings and being slidably arranged inside the outer hollow plunger rod. The inner hollow rod is slidable between first and second positions. The inner hollow rod in the first position has the first opening disposed within the first carpule and the second opening disposed within the second carpule. This allows liquid solvent in the second carpule to flow into the first carpule, which comprises an evacuated chamber containing solid matter that dissolves in the presence of that solvent to form a mixture. The second carpule is then removed and the mixture in the first carpule is injected into the patient.