There are bacteria in the small intestine. The small intestine is the digestive organ of the human body, located in the abdomen, above the origin of the pylorus of the stomach, connected to the large intestine, is the longest organ in the digestive tract, is the main part of the body’s nutrient absorption, is divided into the duodenum, the jejunum and the ileum three parts. A large number of bacteria survive in the small intestine, such as: bifidobacteria, which can assist the intestinal digestion of lactose, inhibit the reproduction of putrefactive bacteria, to prevent diarrhea or constipation; Lactobacillus, which can maintain the acid-base balance in the intestinal tract, repair intestinal injuries, and stimulate intestinal peristalsis; Enterococcus faecalis, which can form the intestinal protective layer, forming a mucous barrier, and maintain the balance of the bacterial flora, and so on. In addition to the above three main intestinal bacteria, there are other beneficial flora, which can form colonies to check and balance each other, but also prevent harmful bacteria from colonizing the intestinal tract and protect the health of the gastrointestinal tract.