An elastomeric stopper that can be partially inserted in a rear opening of a glass carpule and that also serves, when fully inserted in the carpule, as a plunger for forcing fluid inside the carpule out through a front opening thereof. The stopper has a thin central portion at its front end that can be readily pierced by a pointed hollow rod of a syringe. When the hollow rod is removed, the elastomeric material of the thin central portion will “seal itself” around the puncture hole. The stopper also has a retractable lip at its rear end that allows the entirety of the stopper to be pushed down and into a fluid-containing glass carpule, thereby acting as a plunger and ejecting fluid from the front opening of the carpule.