Which nerve is being tested by putting salt on the tip of the tongue?

KEY CONCEPT: The sensory nerve fibers from the taste buds on the anterior two-thirds of the tongue travel in the  chorda tympani branch of the facial nerve and those from the posterior third of the tongue reach the  brainstem via the glossopharyngeal nerve. The fibers from areas other than the tongue (eg, pharynx)  reach the brain stem via the vagus nerve.