Dark and dilute stools indicate a tarry stool, which is directly related to gastrointestinal bleeding. Some people suffer from varices in the fundus of the stomach, peptic ulcers, small intestine vascular malformations, and intestinal tumors, which can cause bleeding in the digestive tract. When there is bleeding in the gastrointestinal tract, blood will be discharged through the digestive system along with the stool, which will then show tarry stools, which are black in color and thick in texture, and will be accompanied by uncomfortable bowel movements. If you have tarry stools, you should go to the hospital for further examination to determine the site of bleeding and to treat the bleeding site. For minor gastrointestinal bleeding, medication can be used to improve the condition, but for severe gastrointestinal bleeding, surgery should be the main treatment, and the patient should fast for a period of time after the surgery and eat normally only after the stool has recovered.