Boil it from 12 hours to 3 days. As the water evaporates, add more. The resulting brew will be so black, so vile tasting and so evil smelling that it will choke you. But boiled bark contains tannic acid and that will help to cure your dysentery. It also can help further and that will help to cure burns.
Tea is another cure because it contains tannin.
Men who'd had chronic dysentery for 2 to 3 years were cured when we got enough tea. Strong tea solutions which contain tannic acid in concentration, have also been used for centuries for burns. Hepatitis Hepatitis, or yellow jaundice, is a liver disease. When you have it, you don't want to eat but you must. We also tried to keep them off duty as much as possible for about 6 weeks after the jaundice had subsided.