The discharge of blood from the anus or blood in the stool is called blood in the stool or bloody stool. Blood in the stool is a sign of bleeding in the gastrointestinal tract. There are many causes of blood in the stool and all diseases that cause vomiting of blood can have blood in the stool. Lower gastrointestinal tract diseases such as bacillary dysentery, amniotic dysentery, ulcerative colitis, intestinal tuberculosis, colon and rectal polyps or cancer, hemorrhoids, and anal fissures can cause blood in the stool, with hemorrhoids bleeding being the most common. The color of blood in the stool varies depending on the site of bleeding. For upper gastrointestinal bleeding caused by gastric and duodenal ulcers, the blood in the stool is mostly tarry or black; for lower gastrointestinal bleeding, the blood in the stool is dark red or bright red. A. When the stool is black or bright red, the following causes should be ruled out 1. Black stool when taking certain herbs orally and charcoal, iron and button. 2, when eating too much meat, pig liver, animal blood or spinach, the stool is black. 3, oral phenolphthalein preparation, the stool is bright red. Second, classification and common diseases 1, according to the location of the lesion classification (1) upper gastrointestinal bleeding: common in gastritis, gastric and duodenal ulcers, hepatic sclerosis, esophageal and gastric tumors, etc. (2) Lower gastrointestinal bleeding: common in anal fissure, hemorrhoids, anal fistula, chronic colitis, bacterial dysentery, amoebic dysentery, colon or rectal polyps, tumors, etc. (3) Systemic diseases: common in hematological diseases, uremia, typhoid fever, renal syndrome hemorrhagic fever, leptospirosis, etc. 2, according to the characteristics of blood in the stool classification (1) bright red, and feces do not mix: common in the anus and rectal bleeding. (2) bright red, mixed with feces: suggests lower gastrointestinal bleeding, including various inflammatory diseases and tumors. (3) Black stool: indicates upper gastrointestinal bleeding, including peptic ulcer, hepatic steatosis, inflammation and tumor, etc.