Spleen has the function of filtering blood. Marginal region and splenic cord are the main places for blood filtration. A large number of macrophages in the spleen can remove aging blood cells (such as red blood cells), antigens and foreign bodies. In addition, antigens invading human blood can stimulate the immune response of spleen. In addition, the spleen can also store blood. Human spleen can store about 40 ml of blood, while horse spleen stores about 30% of red blood cells. In the early stage of embryonic development, the spleen has the function of hematopoiesis. However, the hematopoietic function of the spleen basically disappears after birth, and it can only be restored in some cases (such as serious hematopoietic disorder in human body).