From Team Fortress Wiki
Functionality of this weapon is speculated as having acted similar to the Medkit from Team Fortress Classic. The weapon was removed before release in favor of a healing weapon which would be easier to recognize for its purpose, and would fit in with the goal of providing easily identifiable class silhouettes. As a result, it was replaced by the Medi Gun with its conspicuous healing beam. Additionally, it was decided that the Medic would need to stay in the thick of battle instead of hanging back away from the action. The Medi Gun solved this by being easy to use, as to allow Medic players to focus on survival while healing teammates.
- The model for the Syringe still exists fully textured in the VPK, under the folder