Bone Marrow.

Marrow is a soft matter found inside the long bones of vertebrates that produces red and white blood cells, platelets and lymphocytes. The cells produced by marrow are "stem cells" with the capacity to develop into different kinds of cells. The process by which the marrow makes the components of blood from stem cells is called hematopoiesis. Since the marrow is the only source of blood, it is vitally important that it stay healthy. Diseases that are rooted in or affect the bone marrow and impair the production of blood include leukemia, multiple myeloma, aplastic anemia, sickle cell anemia, polycythemia vera, myelofibrosis, and lymphoma. In addition to disease, bone marrow cells are vulnerable to radiation and to chemotherapy treatments for cancer.