Which part of the syringe allows the applicator to push the medication through the syringe?

The part of the syringe that allows the applicator to push the medication through is the plunger. The plunger is a solid rod that fits snugly inside the barrel of the syringe and is designed to create a seal. When the plunger is pushed down, it exerts pressure on the fluid inside the barrel, forcing the medication through the needle and into the intended area, whether that be an injection or another application.

The barrel, while essential for holding the medication, does not perform the action of pushing; it simply serves as a chamber that contains the fluid. The cap exists to cover the needle and protect it from contamination, and it doesn't serve any functional purpose regarding the administration of medication. The needle is the component that delivers the medication into the body but requires the action of the plunger to function effectively. Thus, the plunger is the critical part for the application of medication from the syringe.