A machine that is used to sort cells from a mixed group of cells (e.g., to remove only the cells into which a new gene has been inserted via genetic engineering techniques). The desired cells are first labeled with a specific fluorescent dye, then passed through a flow chamber that is illuminated by a laser beam, which causes the labeled cells to fluoresce (i.e., glow). The molecules of the fluorescent dye, which “stick” to only one type of cell in the mixture, contain chromophores that can be elevated to an excited, unstable state via irradiation with specific wavelength(s) of light. Those chromophores remain in that excited state for a maximum of 10¯9 seconds before releasing their energy by emitting light, and returning to their unexcited ”ground” state. This fluorescence (glow) is a measurable property and the FACS machine utilizes it to separate the desired cells from the rest of the mixture.