Color enhanced SEM of free surfaces of cultured HeLa cells are seen to be covered by large numbers of long slender microvilli. Cultured cells are particularly useful for scanning microscopy. Uncultured cells would escape detection by light microscopy, and appear to be short and relatively sparse in micrographs of thin sections. These are highly responsive to the nutritional state of the cells and vary in abundance in different phases of the cell cycle. The variation of the one cell is due to cell death - most likely apoptosis. The source of the original cells was Henrietta Lacks whose cells were by chance used by George Otto Gey to culture an immortal cell line for research. This cell line is known as the HeLa cell line.