Why is it that when 1 apply salt to my ulcer it will heal faster?

Heya! :) I'm just curious.. you know whenever I have ulcer & soar throat my mom would always ask me to gaggle or apply salt and it seems to work most of the time. Healing really fast, like by the next day it'll be gone:D Ohoh! And the other time when i had tonsillitis, i gargling salt water and ot seems to help relieve my throat more... why?:P Is it just pure coincidences? Or does salt kill bacteria or something?