We’re sure that at some point in your life you’ve had the unpleasant experience of diarrhea. There are many different causes, including food poisoning and various diseases. The big danger to the patient is dehydration, since each bowel movement is releasing a lot of fluid as well as stools. Concentrate on getting the patient safe drinking water. If the patient’s urine turns dark yellow, increase the amount of fluids you’re giving him. Gradually put him on a carb-heavy diet, avoiding milk and coffee (since caffeine acts as a laxative).
The other side of this is constipation, which can be very painful. Try changing the patient’s diet, but stay away from alcohol, bananas, cheese, and other foods that tend to help bind stools tighter together.
Astringent plants taken as an infusion will help to bind things a bit if you’re suffering from diarrhea. Any plant or tree that is high in tannins is an astringent. Common plants such as yarrow and goldenrod that work well for bleeding are also great candidates for stopping diarrhea. Trees like oaks are also high in tannic acids. Use the inner barks (in emergencies, the leaves will work as well). Crushed acorns are filled with tannin and can be chewed if the means to make an infusion are not available or convenient.