Abstract
Two cell lines were established in vitro from Syrian hamster embryos. The shift of biological characteristics, such as cell morphology, growth rate, the ability to grow at low inoculation density, chromosome constitution and tumor-producing capacity was examined for ten months. The growth rate upon successive transfers declined slowly and about three months after the initial cultures cellular growth stopped. Thereafter colonial growth was performed and the growth rate began to rise which soon reached a value higher than that at the culture onset. No distinctive morphological alteration was observed after the colony formation. Chromosomal studies indicated that the cells before the phase of declining growth rate were diploid, but after colony formation, the population shifted to the hyperdiploid range. The cells implanted periodically into isologous hamsters never gave tumors.
