4) Earle, W. R., Schilling, E. W., Stark, T. H., Straus, N. P., Brown, M. F. and Shelton, E.: Production of malignancy in vitro. IV. The mouse fibroblast cultures and changes seen in the living cells. J. Natl. Cancer Inst. 4: 165-212, 1943.
5) Puck, T. T., Marcus, P. I. and Cieciura, S. J.: Clonal growth of mammalian cells in vitro. Growth characteristics of colonies from single HeLa cells with and without a “feeder”layer. J. Int. Med. 103: 273-289, 1955.