Studies on the Growth of Tissues in Vitro v. Further Observations on the Manner in Which Cell Division of Chick Fibroblasts Is Affected by Embryo Tissue Juice

IT has already been shown (1933, 1936) that chick fibroblasts (mesenchyme cells derived from the heart or from periosteal tissue) can be reduced to a state in which growth by cell division is almost at a standstill and that, by the addition to the medium of embryo tissue juice, the cells can be caused to divide again. The higher the concentration of embryo juice used, the greater is the number of cell divisions which occur. The addition of the embryo juice is followed within the first 2 hours by increased movement of the cells, which reaches its maximum in about 10 hours, but it is not until this latter time that cell divisions begin again. During these experiments the embryo juice, once added, was left in contact with the culture. At the suggestion of Dr Pantin, experiments were undertaken to investigate whether this was a necessary part of the procedure, or whether it is possible to cause cells to divide by the application of embryo juice for only a limited time. The experiments were successful and the results throw interesting light on the process of cell division. There are reported also in this paper certain observations on the duration of the mitotic phases under different conditions and their relationship to cell movement as a whole, the latter being estimated by measuring the average migration rate of the cells during hourly intervals. Finally, some observations have been made on the size of cells during the metaphase of division under various conditions. The experimental procedure was precisely the same as in the previous experiments in that cultures from strains of chick periosteal fibroblasts were grown in flasks in a medium of plasma and Tyrode solution for at least 48 hours, by which time cell divisions had practically ceased to occur. The Tyrode solution was then removed and replaced by embryo juice which remained in contact with the culture for varying lengths of time. Different concentrations of juice (i.e. neat embryo juice diluted with Tyrode solution) were tried and in this way graded responses were obtained from the tissues. When the embryo juice was removed after the required