Tissue culture studies; the relationship of nucleic acid increase to the growth of cells in vitro.

The content of ribo- and desoxyribonucleic acids in chick heart cultures at regular intervals after implanting has been determined both with standard culture medium and with Tyrode's solution alone. With an inadequate medium, both nucleic acids dropped in a consistent manner but ribonucleic acid was affected to a much greater extent. When the medium was adequate for growth, both fractions rose smoothly and paralleled each other closely, after an initial drop. The final content of each fraction was markedly higher than the amount present in the original implant. The fundamental definition of growth and the relationship of these data to it are discussed.