Agrimony
Agrimony, used freely in the manner of tea, will cure an ulcerated mouth, and is good for liver and kidney complaints. 1 ounce to a pint of boiling water. Dose, a wine-glassful three times a day.
Source: Fray’s Golden Recipes for the use of all ages, E. Fray
“Gum Boils” or “Canker Sores”
So-called “gum boils” or “canker sores” are little ulcer-like sores which at times appear in children’s mouths, caused by disarrangement of the stomach. Local applications, such as borax or powdered alum, shrink the sores and give a little relief; but the child should be given a dose of calcined magnesia at night or citrate of magnesia in the morning. (Never give a small dose of citrate of magnesia; a child of twelve years should take a tumblerful.)
Source: The Mary Frances First Aid Book, Jane Eayre Fryer