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Stem cell research. Researchers using a cell screening machine in a stem cell research laboratory. Sample tubes are seen in an ice bath at lower right. The machine sorts the cells by properties such as size, with graphs seen on the screen. Stem cells are cells that differentiate to form the range of different tissues found in the human body. The type of cell they mature into depends upon the biochemical signals they receive. Stem cells, found in bone marrow, umbilical cord blood and embryos, are being studied to find treatments for disorders of the blood and organs such as the heart, brain and kidneys. This work is being carried out at the Genethon facility in Evry, France. (KEYSTONE/SCIENCE PHOTO LIBRARY/PHILIPPE PLAILLY/EURELIOS)