The red blood cells that carry oxygen throughout the body have a lifespan of 120 days. The living body continuously produces blood to ensure a plentiful supply of red blood cells. This film accurately records the conversion of stem cells into red blood cells. Conditions such as encounters with various other cells and contact with signals sent by other cells are important for the growth of blood cells, and the erythropoietin is one of these important signals. This signal stimulates the stromal cells to produce the necessary number of red blood cells which are continuously sent into the bloodstream. Scientific supervisor Fumimaro TAKAKU, M.D. Ph.D. (University of Tokyo)