The in vitro cultivation of cells and tissues forms an integral part of the work of every diagnostic cytogenetics laboratory, since it is from cells undergoing mitosis that metaphase chromosome preparations are obtained. Spontaneously dividing cells suitable for direct chromosome preparations are found only in the rapidly proliferating tissues of the body such as the gonads and bone marrow, or in tissues with mahgnanctes. In order to obtain metaphase spreads from other cells or tissues, it is necessary to induce cell division artifictally.