CARBON DIOXIDE CHANGES UNDIFFERENTIATED CELLS—When carbon dioxide is bubbled into a solution containing undifferentiated cells that have just begun to grow after egg fertilization, the cells become brain cells. Dr. Reed Flickinger, zoologist at the University of California at Los Angeles, is studying the process by which like embryonic cells suddenly begin to specialize to form specific structures such as brain, muscle, skeleton, and reproductive organs. Addition of small amounts of carbon dioxide—large amounts kill the cells—to undifferentiated frog embryo cells caused the cells to form nervous tissue the day after fertilization, Dr. Flickinger said. Three to four days later definite brain structures could be identified. Apparently the carbon dioxide stimulates protein synthesis in the cell by causing release of nucleic acids and storage protein from the yolk granules packed in the cell, the UCLA zoologist said. All cells have equal potential of becoming brain cells…. But some unknown stimulus makes them specialize.